What Is the Treatment for Marfan Syndrome?

Marfan syndrome is also known as congenital mesoderm dysplasia, Marchesani syndrome, spider indications, and limb slenderness. It is characterized by malnutrition of surrounding connective tissue, bone abnormalities, inner eye diseases and cardiovascular abnormalities This genetic disease with connective tissue as the basic defect was first reported by Marfan (1896) as a 5-year-old girl with special slender and long limbs. By 1902, Achard referred to such signs as spider fingers. Salle (1921) had dissected a baby with this syndrome and found that the oval hole was not closed. By 1931, Weve identified this syndrome as a dominant hereditary disease and believed that it was caused by abnormal development of mesoderm tissue.

Marfan syndrome

Marfan Syndrome

On May 11, 2018, the National Health Committee and other five departments jointly developed the "First Rare Diseases Directory", and Marfan syndrome was included. ^[1]

About Marfan Syndrome

Marfan syndrome Marfan syndrome is a congenital mesodermal dysplasia disease, a hereditary connective tissue disease, an autosomal dominant hereditary disease, and an autosomal recessive inheritance in some cases. The specific cause is unknown. It is thought to be related to abnormal congenital protein metabolism. The morbidity of the population is about 4 per 100,000 people. The clinical manifestations of this syndrome are different, mainly involving bones, cardiovascular system and eye and other organs and tissues. It was the first case report by French pediatrician Antoine in 1896, and similar cases have been reported since then. It was officially called Marfan syndrome in 1931.

Marfan syndrome epidemiology

The disease has a familial tendency and is autosomal dominant. Sexual onset, no racial differences, more common in children can also be seen in adults, the incidence of other related content is not described.

Marfan syndrome

Causes of Marfan Syndrome

This disease has an autosomal dominant inheritance. Mucosal polysaccharides such as chondroitin sulfate A or C are accumulated in many tissues of the human body, such as endocardium, heart valves, large blood vessels, and bones, which affects elastic fibers and other connective tissue fibers Structure and function of the organs, resulting in dysplasia and function

Marfan syndrome Abnormality, Abraham et al. (1982) proposed that there are abnormalities in aortic elastin, decreased desmolysin and isomerin, and the corresponding increase in lysyl residues, which is the main change in the urine hydroxyproline excretion of patients There is an increase, and mucin and mucopolysaccharide in the blood also increase.

Pathogenesis of Marfan Syndrome

The dominant inheritance of the family's linked genes can be proved by the increased excretion of hydroxyproline in the patient's urine. The disease is also an elastic fiber defect.

Marfan syndrome That is, collagen metabolism is abnormal. Connective tissue fiber is a very important component in the body's tissue structure. Therefore, when it is abnormal, it will affect the organs (mesoderm tissue) of the whole body, especially the bone and cardiovascular system. Excessive growth of the longitudinal axis of the tubular bones, fingers, and ribs of the limbs in spider fingers, as well as in the sunken chest or scaphoid, may be the result of a defect in the periosteum fiber composition. Acidic mucopolysaccharide deposits in the aorta and pulmonary arteries. The disease has a familial tendency and is autosomal dominant.

Marfan syndrome pathology

Macroscopic changes include eye abnormalities, ascending aorta dilatation, chronic aortic dissection tumors forming myocardial valves with myxedema changes, balloon-shaped valves, tendon thickening, cardiac hypertrophy, mitral valve calcification, and abnormal skin texture. The pathological changes of this syndrome are the most significant in the cardiovascular system and have the generation

Marfan syndrome Expressive. Under the microscope, the aortic middle elastic tissue is sparse and fragmented, with smooth muscles showing irregular thread-like changes, and the amount of collagen is increased. , Shown as cystic middle layer necrosis and moderate degeneration of elastic fibers, accompanied by smooth muscle bundle disorders. The histopathological changes of the aortic valve were destruction and loss of normal structure, cystic degeneration, and loss of tissue fibroblasts. The pathological changes of the skin were manifested as vacuolar degeneration and disordered elastic fiber arrangement. Synovial changes in the joints are also elastic fibrosis, increased collagen, and heterogeneous sac-like distribution.

Marfan syndrome clinical manifestations

Bisexual onset, no racial differences, more common in children, can also be seen in most patients with symptoms after birth, the face is old, showing a sad appearance, thin trunk muscles are not developed, subcutaneous fat is thin.

Marfan syndrome

Marfan syndrome bone changes

The limbs of patients with this syndrome are oddly long and thin, especially the finger (toe). The trunk can be shortened due to the scoliosis, making the limbs more elongated, like spider feet, hence the name of the spider finger (Figure 1). Decreased muscle tone, increased joint activity, and exceptional range of motion, but dislocations are rare. The head is long, the forehead is convex, and the deformities of the sternum are mostly caused by the excessively long ribs. Funnel or chicken breasts are more common, and the scapular hump is wing-shaped. Systemic connective tissue abnormalities can involve the joint capsule, ligaments, tendons, and myometrium, which can cause repeated dislocations of the joints, flat feet or high arched feet, high arches, and irregular teeth. Common Marfan syndrome examination methods:

(1) Metacarpal index: The average length of the four metacarpals of the index finger, middle finger, ring finger and little finger on the anterior posterior radiograph of both hands divided by the average width of the middle of the four metacarpals. The normal human metacarpal index is less than 8 8.4, female is greater than 9.2.

(2) Thumb sign: The patient's thumb is adducted, placed on the palm of the hand to straighten and make a fist. It is positive if the extended thumb clearly extends beyond the side edge of the hand ruler.

(3) Wrist sign: The patient holds the contralateral wrist at the proximal end of the contralateral radial stem with one hand and surrounds it with thumb and little finger for 1 week. It is positive if the thumb and little finger can overlap each other without pressure.

Marfan syndrome skin changes

The most common skin manifestations are widening of the skin lines or atrophic skin lines. These skin abnormalities can be seen in many parts of the body, especially in the chest, shoulder deltoid area and thighs.

Marfan syndrome cardiovascular abnormalities

30% to 40% of patients have cardiovascular complications, the most common cardiovascular abnormalities are idiopathic aortic dilatation, aortic dissection aneurysms, and mitral valve abnormalities. Sometimes aortic disease and mitral valve disease can occur at the same time. Systolic karaoke with late-systolic murmur is its most common sign. In addition, trauma, hypertension, and pregnancy can induce acute aortic rupture and dissecting aneurysm formation. In addition to aortic and mitral valve disease, tricuspid valve disease can occur. Although aortic dilation always occurs in the ascending aorta, thoracic and abdominal aorta can also undergo aneurysm-like dilatation, dissection of aneurysm, or rupture. About one-third of patients may have congenital heart disease. Other rare cardiovascular complications such as aortic stenosis, open ductus arteriosus, and atrial septal defect are Freund s sinus and pulmonary artery dilatation. Such as the common carotid artery and splenic artery dilatation, rupture of endocardial fibrotic aortic aneurysm and heart failure are the main causes of death of this syndrome.

Marfan syndrome eye changes

The most characteristic manifestation is dislocation or subluxation of the lens. About 3/4 of the patients are bilateral. Dislocation of crystals can be caused by a variety of factors. Big eyes and small crystals can increase the space around the lens, expand the ligamentum ligamentum, and undergrow the ciliary body. The ligamentum ligament and its attachment to the lens are abnormal. In addition, this syndrome can also appear high myopia, glaucoma, retinal detachment, iris and other eye abnormalities. These ocular lesions have more severe effects on the eye than lens dislocation. Scleral abnormalities are manifested as blue sclera. Sometimes too large cornea, pigmented retinitis, choroid sclerosis, strabismus, nystagmus, blepharoplasia, and lightening of the anterior chamber

Marfan syndrome neuropathy

The neurological symptoms of this syndrome, like other congenital rheumatism, are also caused by cerebrovascular malformations, which are manifested as seizures caused by aneurysms of compression symptoms caused by subarachnoid hemorrhage and internal carotid aneurysms. In addition, patients with Marfan syndrome can also develop spina bifida, spinal cord bulge, and syringomyelia. Hypotonia and muscle atrophy are the most common neuromuscular symptoms of this syndrome. A small number of patients may have mental retardation or dementia.

Marfan syndrome complications

1. Cardiovascular disease is most likely to occur concurrently with idiopathic aortic dilatation, aortic stenosis, aortic dissection aneurysm, and mitral valve abnormalities.

2. Ocular lesions may be accompanied by lens dislocation or subluxation, high myopia, glaucoma, retinal detachment, iritis, etc.

3. Nervous system diseases can be complicated, subarachnoid hemorrhage, internal carotid aneurysm, and epilepsy. In addition, patients with Marfan syndrome can also develop spina bifida, spinal cord bulge, and syringomyelia.

Marfan syndrome laboratory test

1. Slit lamp inspection can determine the presence of ectopic lens.

2. X-ray examination: the phalanges are slender, and the metacarpal index is 8.4 (that is, the ratio of the length and width of the right 2-5 metacarpals), and the normal is 5.5-8.0.

3. Echocardiography: Visible aortic root dilatation, aortic valve insufficiency, and other concurrent cardiac malformations.

4. CT, nuclear magnetic resonance. More accurate than echocardiography.

Marfan syndrome diagnosis

1. The diagnosis is based on

(1) Special skeletal changes, that is, slender tubular bones, especially the metacarpals. The cortex becomes thin and slender, changing like spider fingers.

(2) Congenital cardiovascular abnormalities

(3) Eye symptoms.

(4) Family history.

Three of the above four clinical criteria can be diagnosed, and only two changes in the first three can be diagnosed as incomplete Marfan syndrome

2.Mckusick (1995) classified cardiovascular abnormalities of Marfan syndrome as

(1) Aortic dilatation (ascending aorta, descending aorta), aortic dissection tumor, aortic valve stenosis, and arterial duct not closed

(2) Pulmonary artery abnormalities (dilated pulmonary artery, pulmonary aneurysm).

(3) Septal defect (atrial septal defect, ventricular septal defect).

(4) Valve abnormalities and subacute bacterial endocarditis.

Differential diagnosis:

This disease needs to be distinguished from the following diseases:

1. Although Ai-Dang syndrome may have symptoms of excessively long limbs and excessive joint movements, Marfan syndrome does not show symptoms of fragile skin and blood vessels and excessive skin extension.

2. Elastic pseudoxanthomatosis can occur in aortic aneurysms and flaccid skin lesions. The lesions are pimples or maculopapular rashes, the borders are clearly dot-shaped, round or oval, or fused into slices. Retinal angioid pigment texture. There is no overkill, no slender limbs and spider fingers.

3. Homocysteineuria is a congenital disorder of methionine metabolism, which may include lens dislocation, abnormal limbs, and abnormal chest and spine. However, abnormal systemic osteoporosis, vascular embolism, and unresponsiveness of urine do not occur in patients with Marfan syndrome.

Marfan syndrome treatment

There is no special treatment, and eye abnormalities can be treated with surgery or medicine. In the case of aortic disease, propranolol (propranolol) can be taken to reduce ventricular blood flow and pressure and reduce the impact on the aortic wall. Therefore, it can delay the development of aortic root expansion and prevent the dissection of aortic dissection aneurysms. For pre-pubertal female patients, estrogen and progesterone can be taken to enter puberty in advance to prevent severe thoracic scoliosis due to too fast growth, patients with spinal deformity, moderate aortic insufficiency or significant expansion of the aortic root Patients can be treated with surgery.

Marfan syndrome prognosis prevention

Marfan syndrome prognosis

Better, most patients survive to middle age and often die from aortic aneurysm rupture and heart failure.

Marfan syndrome prevention

1. Primary prevention of genetic diseases In addition to the prevention of epidemiological surveys from the perspective of the entire population, the carrier of epidemiological surveys, genetic monitoring and environmental monitoring of the population, marriage and fertility guidance, and efforts to reduce the incidence of genetic diseases in the population and increase the population In addition to quality, for individuals, effective preventive measures must be taken to prevent the birth of offspring of genetic diseases (that is, the implementation of eugenics) and the occurrence of genetic mutations. Common measures include: pre-marital genetic counseling, prenatal testing, and early treatment of genetic diseases. .

(1) Pre-marital inspection: Pre-marital inspection (ie marriage health care), it is an important link to ensure the happiness of marriage and the health of future generations. The key points of the pre-marital examination are as follows: The investigation of genetic diseases includes detailed inquiry about the past medical history and treatment of the health status of both men and women and their family members, especially whether there are congenital deformities, genetic medical history and history of close marriage. When necessary, a family survey, blood group examination, chromosome examination, or genetic diagnosis should be performed to detect the carrier; Comprehensive physical examination, mainly for acute infectious diseases, tuberculosis, or severe heart, liver and kidney diseases, chronic urinary tract inflammation, etc. Diseases that seriously threaten the health of the individual or spouse, as well as women's severe anemia, diabetes and other diseases that can affect the fetus, and mobilize to cure before being married; Examination of male and female reproductive organs, detection of sexual organ deformities, Bisexual disorders, so that measures can be taken very early.

(2) Genetic counseling: Genetic counselling is a genetic answer from clinicians to genetic questions to answer the questions about the etiology, inheritance, diagnosis, treatment, and prognosis of genetic diseases. Estimate the probability of a child's child suffering from another disease, and provide suggestions and guidance for the reference of patients and their relatives. The significance of genetic counseling is: to reduce the physical and mental suffering of patients, to reduce the psychological pressure of patients and their relatives, to help them correctly treat genetic diseases, understand the probability of occurrence, and take corrective measures to prevent and treat them; reduce the incidence of genetic diseases in the population Rate reduces the frequency of harmful genes and reduces the chance of transmission

Classification and content of genetic counseling:

A. Pre-marital consultation: Before marriage, both men and women ask whether they can get married when they learn that there is a genetic disease in one of them or their relatives. What is the incidence of the disease in future generations?

B. Prenatal consultation: one of the couple or their relatives has a genetic disease or congenital malformation, and asks about the occurrence of similar diseases in the offspring; if you have had a genetic disease or congenital malformation, ask the offspring at the time of childbearing Situation and how to prevent the birth of the child. During pregnancy, you have had a disease, taken a medicine, or been exposed to toxic substances or radiation, and asked about the possible situation of the fetus.

C. General genetic counseling: In addition to the above-mentioned circumstances, is it also possible to ask whether the marriage between close relatives is possible? The prevention and treatment methods for individuals who have developed symptoms have some symptoms or signs that are suspected to be genetic diseases, and so on.

Although the counselor's age, occupation, knowledge base and cultural level are different, and their intentions and requirements are different, the basic content of genetic counseling can be summarized into the following four aspects: a. Clear diagnosis whether it is a genetic disease; b. Answering each question Problems, including prevention and prognosis; c. Estimating recurrence risk rates; d. Discussing countermeasures. In order to accomplish this, genetic counseling usually includes the following procedures: a. Through medical history and pedigree investigation, physical examination and necessary auxiliary examination and special genetic examination analysis to determine whether it is a genetic disease and how it is inherited; b. Estimate the risk of recurrence according to genetic methods and characteristics; c. Discuss and propose preventive treatment countermeasures and guidance on marriage and fertility through discussions.

Estimation of recurrence risk rate:

A. The risk of recurrence of human genetic diseases can be divided into 3 categories according to their degree of danger:

a. General risk: the incidence is above 1:20. It usually refers to diseases caused by environmental factors (such as rubella infection in the first trimester of pregnancy). It generally has no effect on the onset of subsequent contemporaries. The expected risk is similar to that of the entire group.

b. Mild risk: the incidence is 1:10 to 1:20. Often refers to the risk of recurrence of a polygenic inherited disease, which must be comprehensively analyzed and calculated based on the heredity and threshold of the disease.

c. High risk: the incidence rate is 1: 1 to 1:10. All single-gene hereditary diseases (autosomal dominant hereditary diseases, recessive hereditary diseases, X-associated hereditary diseases) and cases where one of the parents has a balanced translocation chromosome fall into this category.

B. Estimation of the risk of recurrence of genetic diseases: it depends on the genetic diseases and known information of different genetic methods. In the estimation of single gene recurrence risk. Estimates are made for those who have been genotyped and those who have not been genotyped.

a. The genotype is presumed: most patients with autosomal dominant etiology are heterozygous. If the penetrance is 100% and the parent is a patient, the child's probability of illness is 50%. If one or more patients have been born, The risk of recurrence is still 50% when both parents are patients, and the child's recurrence risk is 75%. Children whose parents are not patients generally do not develop the disease. The risk of recurrence in children of mutant individuals is 50%, and their sibling incidence is equal to the population's natural mutation rate. If the manifestation is incomplete, the child's probability of illness is K / 2 (K is the penetrance rate, which is the percentage of the actual observed illness and the expected value).

Autosomal recessive disease: The risk of offspring is closely related to the condition of the parents. In the case of close relatives, the risk of getting sick is increased.

X-associated dominant genetic disease: male patients with normal females, their children are normal males, females develop disease. 50% of the children of males who are normally married to female patients are affected.

X associated recessive genetic disease: 50% of male patients' brothers are likely to develop the disease, while their sisters are not, but 50% are carriers, and the overall incidence of siblings is 25%; their children are generally not affected, but their daughters are Carriers, 100% of the offspring of female patients, and daughters are carriers. Male patients are matched with female carriers, and 50% of their children are affected. Female carriers are matched with normal men, half of the children are boys, and half of the girls are carriers.

Y-associated genetic disease: generally manifested as paternal transmission, and offspring transmission is limited to men.

b. Those whose genotypes have not been estimated: If the genotype of one or both parents is unknown, it is much more complicated to estimate the risk of recurrence of children with onset or later born children. Because of the late onset of overt genetic diseases, heterozygotes do not develop until a certain age. A healthy child may be completely normal, or it may be a heterozygote that has not yet developed disease. To estimate the risk of recurrence, the probability of being a heterozygote must be estimated. In a family of recessive genetic diseases, parents with normal phenotypes and normal children cannot be concluded that they are not genetic carriers, because even if both parents are heterozygous, the probability of having a normal child is 3/4. Of course, the more normal children they give, the less chance they are heterozygous. In this case, the risk of recurrence can be estimated by using the inverse probability law (Bayes's law) according to the phenotypes of the previous and next generations, and the results of experiments.

There are multiple pairs of pathogenic genes in polygenic genetic diseases, which are co-dominant; each gene has a small role but has an additive effect, and in addition to the genetic basis, environmental factors play a greater role in the pathogenesis of polygenic genetic diseases. Different polygenetic diseases have different heritability, and the incidence thresholds are different. It is more complicated to estimate the recurrence risk rate. In general, if the heritability of polygenic diseases with high heritability (70% to 80%) is 0.1% to 1%, the incidence of first-degree relatives of patients is similar to the square root of the incidence of the population. Several issues should also be considered for illustration.

The population incidence of cleft lip in China is 0.17%, heritability is 76%, the incidence of first-degree relatives of patients is 4%, which is close to the square root of 0.17%; when a couple has two children with cleft lip, the risk of recurrence Corresponding increase, the incidence rate increased from 4% to 10%; if the patient is seriously ill, the risk of morbidity will be higher than the milder one. The incidence of first-degree relatives of patients with cleft lip on one side is 2.6%, and those with cleft lip on both sides and cleft The risk of recurrence can be as high as 5.6%. When there is a gender difference in the incidence, the recurrence risk of first-degree relatives of patients with a low incidence is higher than that of first-degree relatives of patients with a high incidence; Malformations account for 1% to 2% of newborns. The risk of developing such malformations when a child with one of these deformities is born increases with the number of existing patients.

The parental karyotype of most children with chromosomal disease is normal, and the offspring will develop due to chromosomal abnormalities during germ cell development. The sib risk of this type of siblings is the same as that of the general population; the risk of recurrence of elderly women or parents with obvious mutagenic contact history can be significantly increased; the number of chromosomes is abnormal (such as the three chromosomes of 13, 18, 21, etc.) Physical syndrome), if the karyotype of one of the parents is chimeric, the risk rate of regenerative children can be estimated using the formula P = [X / (2-X)] ÷ K (P is the risk rate, X is The percentage K of trisomy cells is a coefficient, usually 2). The calculation of the risk of recurrence of diseases caused by chromosomal structural aberrations requires the analysis of possible types of separation and exchange according to different types of aberrations. Finally, the analysis is based on the laws of separation and exchange. Only the situation of gametes can be estimated.

Proposing countermeasures and answering questions: The genetic counseling work should thoroughly understand the medical history and family conditions, analyze the genetic methods and estimate the risk of recurrence, and then answer the questions raised by patients and their families, and prevent and treat genetic diseases. Propose countermeasures and give guidance on marriage, fertility, etc. In order to effectively prevent the occurrence of genetic diseases and benefit humanity.

(3) Prenatal diagnosis: prenatal diagnosis (also known as intrauterine diagnosis) or prenatal diagnosis (antenatal diagnosis) is through the detection of fetal sex and health status during pregnancy in order to take necessary measures in a timely manner Prevent the birth of children with genetic disease or congenital malformations. Prenatal diagnosis is the product of a combination of biochemical genetics, cytogenetics, molecular genetics, and clinical practice. The development of today's high-resolution banding technology, genetic engineering technology, and villus aspiration and culture technology makes prenatal diagnostics more widely applicable. , The inspection results are more accurate.

Objects of prenatal diagnosis:

There are three types of genetic diseases commonly encountered in prenatal diagnosis:

Category 1: chromosomal abnormalities, which account for about 0.5% of total births due to easy diagnosis. It can account for 1/4 to 1/2 of prenatally diagnosed cases.

Category 2: Monogenic disease, which generally accounts for 3.5% of total births and 10% of prenatally diagnosed patients

Category 3: Polygenic diseases include anencephaly, spina bifida, hydrocephalus, some cleft lip and palate, and some congenital heart disease. Mainly neural tube defects, accounting for 40% to 50% of prenatally diagnosed cases.

There are some differences in the indications for prenatal diagnosis in different countries and hospitals. The areas with good general health care conditions and broader hospitals generally have widely accepted indications including the following:

A. Senior pregnant women over 35

B. Pregnant women with abnormal chromosome number or structure on one side of the couple.

C. Children with trisomy 21 or other chromosomal abnormalities and pregnant women with a corresponding family history

D. Pregnant women with fragile X chromosome families.

E. The spouse is a pregnant woman who is a carrier or chimera of a chromosomal equilibrium translocation or other chromosomal aberration.

F. The spouse is a patient with a genetic disease, or a pregnant woman who has had a child with a genetic disease.

G. A pregnant woman with a neural tube defect on one side of the couple, or who has had an open neural tube defect (no brain, spina bifida).

H. Pregnant women with a history of unexplained spontaneous abortion, stillbirth, and neonatal death.

I. Pregnant women who have been exposed to large doses of radiation or virus infection during the first trimester

J. Pregnant women with polyhydramnios.

K. Pregnant women with significant exposure to environmental carcinogens and teratogenic mutations.

Prenatal diagnosis methods: Prenatal diagnosis can be divided into maternal screening and fetal examination according to the inspection object. Among them, maternal screening can include maternal blood serum alpha-fetoprotein screening, maternal circulating blood fetal cell examination, and the like. The prenatal diagnosis usually refers to the examination and diagnosis of the fetus. It can be performed at different levels, using different methods

A. Morphological level (phenotypic level): Mainly check the fetus for congenital malformations. The commonly used methods are:

aX-ray examination: After 16 weeks of pregnancy, long bones, short bones, ribs and other bones of the fetus have been ossified, and the malformation can be diagnosed by X. When necessary, water-soluble or oil-soluble contrast agents can be injected into the uterine cavity for amnioingraphy.

b. Ultrasound diagnosis: Ultrasound diagnosis is a simple and minimally invasive prenatal diagnosis method. Commonly used ultrasound diagnostic instruments are A-type ultrasound diagnostic equipment, B-type ultrasound diagnostic equipment, ultrasound Doppler diagnostic equipment and M-type ultrasound diagnostic equipment. The B-type ultrasonic diagnostic instrument (B-ultrasound) has the advantages of large contrast of light spots and high resolution of the image. Multi-probe electronic automatic fast scanning improves the scanning speed and can directly observe the fetal heart. The fetal movement and other dynamics can be recorded and analyzed. B-ultrasound is commonly used to detect: multiple pregnancies; placental location; gender identification; neural tube malformations; visceral malformations; fetal erythrocytosis; abnormal embryonic development; intrauterine growth retardation.

c. Fetalscope: A fetoscope is a fiber-optic endoscope with a double cannula with amniocentesis. After insertion into the amniotic cavity, fetal malformations can be directly observed, and fetal tissues and fetal blood, villi and other materials can be collected. Some intrauterine treatments can also be performed, which provides a new way for the pretreatment of genetic diseases, but this operation can cause miscarriage. Amniotic inflammation, maternal immune response, and other complications, so its application is limited.

B. Chromosome level: The chromosome examination of the fetus in the uterus can diagnose and prevent common chromosome diseases such as fragile X syndrome, chromosome break syndrome, and malignant tumors related to chromosomal abnormalities, and can predict the fetus's gender favorableness. Prevention of linked genetic diseases. The commonly used materials are exfoliated cells and villous cells in amniotic fluid. Generally, after tissue culture, chromosome slices are prepared for karyotype analysis and high-resolution band detection, and X and Y body tests can also be performed directly. Villous cells can also be made for observation immediately after short-term culture. Existing data show that the results of chromosome analysis of villous cells and chromosome analysis of amniotic fluid cells are inconsistent. A summary of 1401 examinations in 21 European centers indicated that: a. The abnormal chromosome rate of villi is higher than that of mid-pregnant amniotic fluid cells; b. The presence of autosomes The total number of mutations is three times higher than that of mid-pregnant amniotic fluid cells, and some non-viable trisomy (such as trisomy 14, 15, 16) are found; c. The rate of sex chromosomal abnormalities is also 3 times that of amniotic fluid cells, of which 45X is 10 times higher than amniotic fluid cells D. One of the couples has a balanced chromosomal translocation, and those with villous chromosomes have an unbalanced translocation are also higher than amniotic fluid cells; e. The risk of recurrence of chromosomal abnormalities detected by villous cells is 4.16%, and amniotic fluid cells are 1.5%. The inconsistent diagnosis of chorionic villi and amniotic fluid cells in early pregnancy can at least suggest that during the development of the embryo, the selection of nature constantly eliminates abnormal cells, but the other significance is unknown.

C. Enzymatic level: Many congenital enzyme abnormalities can be detected through enzymatic examination of amniotic fluid and cells, villous cells or maternal hematuria.

D. Metabolite levels: specific metabolites can be detected, and certain genetic metabolic diseases such as mucopolysaccharidosis can be diagnosed in advance.

E. Gene level: using amniotic fluid cells, villous cells or fetal biopsies or fetal cells in maternal peripheral blood as materials, using extremely sensitive and specific genetic diagnostic technology to detect children with genetic diseases

In recent years, with the development of in vitro fertilization, blastocyst culture, single cell microscopy, artificial embryo transfer and other technologies, a pre-implantation diagnosis (also known as pre-implantation diagnosis) has emerged. It uses modern molecular biology techniques such as PCR, in situ hybridization and other highly sensitive and specific detection methods to analyze the genetic composition of single cells or several cells in in vitro fertilized embryos or blastocysts obtained by uterine lavage. In order to determine whether it is a carrier of pathogenic genes and to transfer healthy embryos into the mother to continue development, this is another development of prenatal diagnostic technology, but it is still immature and cannot be promoted.

Amniocentesis: The amniotic cavity is formed on the seventh day of fertilized egg development, and amniotic fluid is generated, and the amniotic fluid is in direct contact with the fetus. It is one of the main supply channels of nutrients required for fetal development, and is also the place where fetal urine is excreted. Its composition can reflect the growth and metabolism of the fetus. Therefore, amniotic fluid and fetal cells shed in amniotic fluid are the main materials for prenatal diagnosis. The successful application of endocentesis is the key to specimen collection. The following introduces the technical points of amniocentesis

A. Indications and contraindications for amniocentesis: All pregnant women who need clinical and other information suggesting prenatal diagnosis are indications for amniocentesis. Generally, the contraindications are: a. Pregnancy less than 12 weeks (the uterus is too small) ) Or more than 24 weeks (cell culture is not easy to succeed); b. Indications are not clear; c. Pregnant women with threatened abortion or missed abortion; d. Those with pelvic cavity or intrauterine infection; e. Those who predict fetal sex simply because of social customs

B. Time for amniocentesis: preferably 16 to 20 weeks of pregnancy. The reasons are: a. At this time, the amount of amniotic fluid is large (more than 170ml), and 20ml of amniotic fluid is drawn quickly, which will not cause abortion due to a small official cavity. The puncture is not easy to hurt the fetus; c. The proportion of viable cells in amniotic fluid cells is the highest at this time, and it is easy to culture successfully; d. The epithelial cells and fibroblast-based amniotic fluid cells are suitable for enzyme and biochemical analysis.

C. Puncture method: The following preparations need to be done carefully before puncturing:

a. Check for indications, weeks of pregnancy, and uterine size for complications.

b. Examination of peripheral blood leukocytes, hemoglobin and blood type.

c. Check the skin of the puncture site for dermatitis and infection that are not conducive to puncture.

d. Select the appropriate puncture site. You can use B ultrasound to help locate the placenta and determine whether it is a single puncture. It can also be performed under the guidance of B ultrasound.

e. The pregnant woman must empty the urine before puncture. The most suitable puncture site is 3 horizontal fingers on the pubic bone, and the best uterine floor near the midline of the abdomen is between the umbilical shame, or 2 horizontal fingers below the umbilicus, so that the needle insertion site is just in the uterus. You should palpate carefully at the center or slightly below the needle. The puncture adopts a 21-gauge needle (with core). General steps: disinfect the puncture site and the surrounding skin, lay a hole towel, local anesthesia, and quickly insert the needle vertically, and then slowly insert the needle to a depth of 7 to 8 cm after entering the skin (there may be a feeling of emptying when entering the uterine cavity), and extract the light yellow transparent liquid Is amniotic fluid (Figure 2). First draw 1 ~ 2ml for biochemical examination. Precipitated cells can be used for sexual chromatin examination. Another 15ml is drawn into a sterile test tube for cell culture.

D. Common problems in amniocentesis:

a. Puncture failure: The general failure rate is only 0.5% to 1%. Possible reasons are: the uterus is too small, or the puncture site is too low, and the urine in the bladder is mistakenly penetrated; the abdominal wall is too thick and the needle is not deep enough; the puncture is to the placenta attachment site, and the blood is not dare to continue the needle and then withdraw.

b. Amniotic fluid with blood: if the hemorrhagic amniotic fluid is drawn at the beginning, it is suggested that the needle tip is still in the palace wall. It is advisable to pierce the needle deeply. After the amniotic fluid is drawn out, change it to a clean syringe and then draw the transparent amniotic fluid. If the amniotic fluid is pumped smoothly and there is always blood, the needlepoint may puncture the carcass or the placenta and cause bleeding, which is more likely to occur in pregnant women with placenta previa

c. Damage to pregnant women and fetuses: In rare cases, puncture wounds to the lower abdominal wall arteries of pregnant women are formed, resulting in large hematomas and shocks; puncture on the placenta to form post-placental hematomas and cause abortion; puncture wounds and fetal skin, after birth Fetal dents; stab wounds to the fetus causing necrosis of the lower extremities.

d. Infection in the official cavity: due to mistakes in the operation, bringing bacteria into the official cavity can cause intrauterine infection and fetal death. Therefore, extreme care must be taken when operating, and the concept of sterility must be strictly controlled.

e. Abortion: The general incidence is very low. May cause miscarriage due to puncture needle eye bleeding bleeding

f. Rh blood group problems: pregnant women with Rh negative blood group may suspect fetal Rh blood group incompatibility, and the pregnant woman can be injected with anti-D globulin after puncture. If the placenta is attached to the back wall, it is not necessary.

g. Application of amniocentesis: Table 2 lists the scope of application of amniocentesis in prenatal diagnosis. Here only the technical details of amniotic fluid cell culture and biochemical examination of amniotic fluid are further explained.

h. Note for amniotic fluid cell culture: Amniotic fluid cell culture is to obtain more fetal cells to meet the needs of other examinations. Most of the amniotic fluid cells are amniotic epithelium and fetal exfoliated epithelial cells. To be cultured successfully, you should pay attention to: a certain proportion of viable cells; the type of culture medium and calf serum must be selected, and the success rate of HamF10 and HamF12 medium is high. , Calf serum or bovine embryo extract contains auxin, which is very important to promote the growth of viable cells; promote early adherence of amniotic fluid cells, generally 5 to 7 days for adherence, mostly epithelial cells at the beginning of adherence, change After the solution, fibroblasts grow in large areas; pay attention to the factors that affect the survival of cultured cells. The growth of cultured cells is too fast or too slow to take into account the contamination of maternal cells; chromosomal mutations occur when cultured in vitro. Need to be identified; other influencing factors: the use of fungal and mycoplasma-contaminated antibiotics, the contamination of blood cells in amniotic fluid, and the effects of other culture conditions.

i. Biochemical examination of amniotic fluid: Changes in the biochemical composition of amniotic fluid can directly reflect the growth and development of the fetus. Detailed biochemical analysis of it can provide a lot of information about genetic diseases. Such studies are now more and more. Table 3 lists several common biochemical indicators of amniotic fluid and their corresponding genetic diseases.

Significance of prenatal diagnosis: Prenatal diagnosis can determine whether a certain genetic disease or congenital malformation exists before the fetus is born. It can also determine whether it is a carrier of a certain genetic variation through accurate chromosome analysis and genetic diagnosis. Provide the most direct basis for clinical disease prevention and prevention of genetic diseases at all levels. Comprehensive analysis can be performed based on clinical data, auxiliary survey data, group survey data, and prenatal diagnosis results, and necessary measures are taken in a timely manner, such as the selective termination of pregnancy of a sick fetus and genetic diseases that can be treated early (such as phenylketonuria) For treatment, some simple congenital malformations can also be treated with intrauterine surgery. Prenatal diagnosis has become an important basic method of modern eugenics. It plays an increasingly important role in helping to limit the spread of disease-causing genes in the entire population, reduce the incidence of genetic diseases, and monitor the genetic quality of the birth population. With the improvement of medical and health care conditions, the indications for prenatal diagnosis continue to expand, and it also provides a lot of first-hand information for the research of medical genetics.

2. Secondary and tertiary prevention of Ai-Dang syndrome From the perspective of genetic disease prevention, the treatment of genetic diseases belongs to the category of secondary and tertiary prevention. The key to the treatment of genetic diseases is: early detection and early treatment. The timing of treatment mainly includes the following: After the diagnosis is confirmed before birth (prenatal diagnosis), prenatal treatment (intrauterine treatment) or immediate postnatal treatment can be performed. There are two types of intrauterine treatments: pregnant women and direct treatment of the fetus. As long as the medicine used can pass through the placenta, the method of administration for pregnant women is convenient, safe, and easily accepted. Such as pregnant women taking biotin, vitamin B12, adrenocortical hormone, digitalis, etc., can treat fetal biotin-dependent carboxylase deficiency, vitamin B12-dependent metabolic acidosis, congenital adrenal hyperplasia and congenital Supraventricular tachycardia. For drugs that cannot pass through the placenta, they can be directly injected into the amniotic cavity to allow the fetus to swallow the drugs together during the swallowing of amniotic fluid. Such as direct injection of thyroxine in amniotic fluid can treat hereditary goiter. Fetal surgical treatment has also been successfully reported; diagnosis of typical symptoms (pre-symptom diagnosis) and early treatment after diagnosis. For example, children with phenylketonuria can be diagnosed early with the Guthrie blood spot filter paper bacteria inhibition method after 72 hours of breastfeeding. The treatment with a low phenylalanine diet can prevent the child's intellectual damage; Only after all symptoms appear Was diagnosed. At this time, damage to organs and tissues has already occurred, and there are not many treatment methods, and the efficacy is not good. Surgery (removal of damaged organs, repair and replacement, etc.) and medical symptomatic treatment can be used to improve symptoms.

The general principle in the treatment of genetic diseases is to ban their taboos, remove the rest, make up for what they lack, regulate the metabolic balance, and prevent the emergence of symptoms.

(1) Correcting metabolic disorders: This is currently the most important method for treating hereditary metabolic diseases. As the understanding of the pathogenesis and intermediate processes of hereditary metabolic diseases continues to deepen, the scope of application of this method is also expanding.

Diet control (forbidden): when metabolic abnormalities cause certain essential substances in the body to be deficient, supplement them through diet; and when the accumulation of metabolites occurs, limit the intake of this metabolite or its precursors to maintain balance . Low phenylalanine diet is a good example for patients with ketonuria. In addition, you can reduce intake by limiting the absorption of specific substances. For example, patients with phenylketonuria who take phenylalanine aminohydrolase capsules can Phenylalanine in food is converted into transphenyl acrylic acid and eliminated.

Reduction of substrates (remove the rest): When diseases are caused by the production of harmful substances through metabolism, the diseases can be controlled or improved by reducing the harmful substrates and reducing the concentrations of their precursors and metabolic derivatives, and removing or reducing their toxic effects. Symptoms. The main methods are: A. Chelation or promotion of excretion; B. Plasma exchange and affinity binding; C. Alteration of metabolic pathways; D. Surgical bypass surgery; E. Metabolic inhibition.

Product replacement (make up for what it lacks): When the important enzymatic reaction products are insufficient to cause disease, the corresponding necessary end products can be directly supplemented, such as growth hormone for pituitary dwarf patients, and anti-blood for patients with hemophilia. Dystrophin (coagulation factor), which gives patients with genetic immunodeficiency the corresponding immunoglobulin.

(2) Correction of abnormal enzyme activity:

Coenzyme supplementation: some genetic diseases, abnormal enzyme activity may be involved:

A. A binding site for a specific coenzyme or vitamin.

B. Active coenzyme transport or biosynthetic processes cause abnormalities Many coenzymes are necessary for normal enzyme activity. Therefore, supplementing the coenzyme component is also an effective method to induce an increase in enzyme activity. It can slow down the degradation rate of the whole enzyme in the cell, increase the half-life of the enzyme, and reduce the Mie constant (Km) of the enzymatic reaction. Use this method to treat more than 25 genetic diseases. Such as the use of cobalamin (B12) to treat a variety of anemia and methylmalonic aciduria.

Enzyme induction or feedback inhibition: Another therapy for enzyme deficiency levels is to use drugs to increase residual enzyme activity to improve metabolic levels. For example, phenobarbital and related drugs can obviously stimulate the formation of the endoplasmic reticulum of the smooth surface, and can accelerate the synthesis of specific enzymes in the endoplasmic reticulum, including liver UDP glucuronyltransferase. And Crigler Najjar syndrome provide the theoretical basis.

Feedback inhibition is an important form of many metabolic regulation. For the substrate or its precursor accumulation caused by a certain enzyme defect, the feedback inhibition of other bypass metabolisms can be used to increase enzyme activity, reduce accumulated substrates, and feedback. Inhibition has been used as a treatment for acute porphyria.

Allogeneic transplantation: By implanting the same type of cells, tissues or organs containing normal genes into individuals with genetic diseases, in order to produce corresponding active enzymes and other gene products in the recipient, the therapeutic purpose is achieved. The graft may function in the recipient through two mechanisms:

A. Produce active enzymes and metabolize in situ to remove the original storage substrate.

B. Release active enzyme, coenzyme or immune active factor into blood, and distribute it to other tissues in the body to play a role. Tissues and organs that have undergone such allografts so far include kidney and liver, adrenal bone marrow, thymus, spleen and pancreas, and some have achieved significant results.

enzyme replacement therapy: directly provide patients with enzyme deficiency with the corresponding normal enzyme. With the development of enzyme technology, cell engineering and genetic engineering technology, it is possible to provide sufficient and high-purity enzyme preparations. This enzyme preparation must have the characteristics of long half-life, low antigenicity and good orientation. The commonly used methods for this are:

A. Use microcapsules, liposomes, erythrocyte vesicles and other carriers to package enzyme preparations to reduce immunogenicity and extend half-life

B. Application of receptor-mediated molecular recognition to improve orientation.

C. For some lysosomal storage diseases, the sediment can diffuse into the blood and maintain dynamic balance can be treated by "balance-removal" method.

(3) Gene therapy: Gene therapy refers to the use of gene transfer technology to directly introduce genetic material into germ cells or somatic cells to play a new role in the treatment of genetic diseases and other diseases. Gene therapy of genetic diseases is expected to fundamentally correct the phenotypic abnormalities of genetic diseases.

Basic strategies for gene therapy: In the past 10 years, gene therapy research has been proposing many new ideas and new ideas. The main strategies are:

A. Gene in situ correction (replacement): The purpose of this strategy is to repair the mutated gene in situ without affecting the structure and function of other genes around it. Among them, the in situ correction is directed to the point mutation or small-scale mutation of the gene, and it is intended to repair the site by specific methods. In situ replacement, we want to remove genes with a wide range of mutations and replace them with normal genes. This strategy is the most ideal and direct way to cure genetic variation. At present, many site-specific integrations (homologous recombination) in mammalian cells have provided theoretical and experimental evidence for this strategy, but so far it has not been used For human trials.

B. Gene augmentation (gene augmentation or gene complementation): Transfer of foreign functional genes into diseased cells or individual genomes without compromising the defective genes themselves, and make them expressed to compensate for the loss of function of the diseased genes. This strategy is the most researched and mature method at present.

C. The introduction of antisense genes or other genes that resist the expression of abnormal gene products into cells has an inhibitory effect or is referred to as gene inhibition therapy or intercellular immunity.

Technical Points of Gene Therapy Among the many strategies of gene therapy, the most mature, mature and applied in clinical trials is the strategy of gene enhancement. The whole research process usually includes preclinical research and clinical research. See Table 4.

A. Choice of disease: At present, single gene defect disease is the first choice for gene therapy. The basic conditions for selection often include:

a. The genetic basis is relatively clear, the target gene can be cloned in vitro

b. Gene expression does not need to be fine-tuned and is often open, and those with low physiological levels of products are better.

c. Those with certain morbidity and greater harm, who lack other effective treatment measures.

China is one of the earliest countries for gene therapy research. Xue Jinglun of Fudan University and others chose hemophilia as the research object based on these conditions, and have achieved very good results and reached the world advanced level. Of course, these conditions are limited to the current level of research.

B. Selection of target cells: Target cells for gene therapy can be divided into two categories: germ cells and somatic cells. This led to the classification of germ cell gene therapy and somatic cell gene therapy. If genetic repair or replacement of germ cells or early embryonic cells can be used to correct genetic defects, genetic diseases can be treated not only in the contemporary era, but also pass on new genes to the next generation, and also reduce a harmful gene for the population, which is ideal. Means to cure genetic diseases. However, due to the limitations of modern biotechnology, theory, and the ethics, morals, and laws of human society involving germ cell gene manipulation, animal testing can only be performed for a long period of time. Human trials of gene therapy are limited to somatic cells. Has been used as target cells: hematopoietic stem cells, hepatocyte fibroblast endothelial cells and lymphocytes.

C. Gene transfer vectors and transfer methods: Constructing appropriate transfer and expression vectors and selecting efficient gene transfer methods are the key to gene therapy. Commonly used vectors are: retroviral vectors, plasmid vectors and adenovirus vectors, and adeno-associated virus Carriers, as well as liposome carriers. There are four types of commonly used gene transfer methods.

a. Chemical method: mainly calcium phosphate precipitation method.

b. Physical method: Conductivity and microinjection are commonly used.

c. Membrane fusion method: better liposome encapsulation method

d. Viral method: mainly refers to retrovirus and adenovirus-mediated gene transfer.

Prospects of gene therapy: The concept of gene therapy has been put forward for decades, and it has only reached a decade. With the development of modern molecular biology technology (especially DNA recombination technology), this concept has gained a strong theoretical basis. With the support of technical methods, and was able to be implemented in 1990, two patients with severe immunodeficiency caused by adenosine deaminase (ADA) deficiency received gene therapy successfully, which indicates that the research of gene therapy has entered a new stage. Since then, biomedical scientists from all over the world have carried out comprehensive research on gene therapy with the strong support of various government departments and various forces in society. From the original development of a single genetic disease to tumors, infectious diseases and other diseases, new concepts and new approaches such as gene regulation therapy and gene suppression therapy were proposed. By the first half of 1994, more than 100 clinical trial protocols had been approved for implementation, and some have achieved good results. Of course, the history of gene therapy development is not long, and it needs a lot of research and exploration to be widely used in clinical, especially the following issues:

A. A deeper understanding of the molecular basis of more genetic diseases and the regulation mechanism of gene expression, which is the basis of gene therapy

B. Constructing vectors that are more efficiently and safely expressed and transferred.

C. Establishment of simpler and more effective gene transfer methods.

D. Perfection of technologies such as fixed-point integration and in-situ repair systems.

E. More and closer to the establishment of actual animal models (especially transgenic animal models), this is the only way for preclinical trials of gene therapy.

F. Somatic gene therapy, germ cell gene therapy, ethics and related scientific and technological management legislation.

G. It is also necessary to fully consider the possible hazards of gene therapy, such as the serious consequences caused by insertion mutations, the hazards of reconstitution of defective viral vectors after recombination, and other potential hazards of foreign gene transfer into the body. In short, we believe that gene therapy, as the only way to start with the genetic defect itself, is expected to completely cure the new type of treatment for genetic diseases. It has a very attractive future, but it still needs to be deepened from the basic theory, technical methods and ethics. Extensive research and exploration can adapt to the modern medical model and be accepted by people, and truly become an effective means of preventing and treating human diseases.