What Are Lysosomal Storage Diseases?
Lysosomal storage disease (LSD) is a group of hereditary metabolic diseases that are caused by genetic mutations that cause defects in the acid hydrolase in the lysosome, causing the corresponding biological macromolecules in the body to fail to normally degrade and are stored in the lysosome Accumulation, causing disorders in the function of cellular tissues and organs.
Lysosomal storage disease
Lysosomal storage disease (LSD) is a group of hereditary metabolic diseases that are caused by genetic mutations that cause defects in the acid hydrolase in the lysosome, causing the corresponding biological macromolecules in the body to fail to normally degrade and are stored in the lysosome Accumulation, causing disorders in the function of cellular tissues and organs.
- Chinese name
- Lysosomal storage disease
- Shorthand
- LSD
- Category
- Hereditary metabolic diseases
- influences
- Disturbance of cell tissue and organ function
Lysosomal storage disease
The characteristics of lysosomal storage disease are based on the complexity of the storage and the difference in the tissue distribution and accumulation rate.
Lysosomal storage disease can cause pathological changes in many systems, or it can be limited to the nervous system. It can develop from birth to adulthood. The clinical manifestations are large and the condition is progressively worse. Most lysosomal storage disorders are inherited in an autosomal recessive manner. Although the incidence of each of these diseases is low, it is one of the common human genetic diseases as a group of diseases.
Currently there are no effective treatments for this group of diseases, but case diagnosis and prenatal diagnosis can be performed by measuring the activity of lysosomal enzymes to prevent the birth of children.
Common lysosomal storage disease in China
Mucopolysaccharidosis
The disease is caused by the lack of enzymes required for the degradation of acidic mucopolysaccharides. It is clinically divided into 7 types, with a total of 11 enzymes. Except for MPS-C, MPS-D and MPS-IX It can be detected that MPS- is X-linked recessive inheritance, and the rest is autosomal recessive inheritance.
Mucolipid storage disease
Mucolipid storage disease is a rare autosomal recessive genetic disease caused by the inability to transport lysosomes into the lysosome, resulting in the secretion of lysosomal enzymes outside the cell. Clinically, it can be divided into three subtypes: , and . Enzymatic tests in the laboratory showed that a variety of lysosomal enzyme activities were significantly increased, which was 10 to 30 times the normal human enzyme activity.
Sphingolipid storage disease
It refers to the deficiency of lysosomal acid hydrolase required for sphingolipid degradation or the lack of sphingomyelin-activating protein, causing different sphingolipids such as cerebroside, ganglioside or sphingomyelin to be stored in the lysosome, Causes central nervous system and other tissue lesions. Fabry disease is X-linked recessive and the rest are autosomal recessive.
Oligosaccharide storage disease
It is due to the lack of lysosomal acid hydrolase required for the degradation of carbohydrates in glycoproteins and glycolipids, resulting in the accumulation of different glycosides.
Glycogen storage disease type
It is clinically divided into 11 subtypes. Only glycogen storage disease type belongs to lysosomal storage disease, which is caused by acid alpha; -glucosidase deficiency. At present, this disease is diagnosed by skin biopsy, culturing skin fibroblasts, and detecting alpha-glucosidase activity in skin fibroblasts. It is the only type in the laboratory testing of lysosomal storage disease that cannot be detected by peripheral blood ( The method for detecting this enzyme in peripheral blood is under development).
Laboratory inspection
Laboratory tests for lysosomal storage disorders include:
(1) Urinary toluidine blue screening: As the initial screening of MPS, if positive, MPS-related defective enzymes will be tested; if negative, MPS will be ruled out, and the possibility of ML should be considered in combination with the clinic.
(2) Enzymatic test: This is the gold standard for diagnosis. The relationship between specific enzymes and diseases is described above.
(3) Genetic analysis: Finding genetic mutations can be used to detect heterozygotes. At the same time, genetic analysis combined with enzymatic detection can improve the accuracy of prenatal diagnosis.
Prenatal diagnosis
As most lysosomal storage diseases do not have effective treatments, the birth of such children will undoubtedly bring a heavy economic and spiritual burden on society and families, especially some children with early onset, rapid disease progression and short survival. . Such families urgently need to have children again, but there are high risks of childbearing again. How to avoid the risks and provide them with necessary fertility guidance has become an urgent need for families of children with lysosomal storage disease.
The requirements for prenatal diagnosis include two aspects:
(1) Prerequisites: An accurate diagnosis must identify which enzyme is defective. In addition, it should be noted that the cause of the disease in some cases is a defect in the activated protein related to enzyme activity. In this case, prenatal diagnosis cannot be performed by measuring the enzyme, but can only be resolved by genetic analysis.
(2) Material collection time: The villi (except MPS, ML) were taken during the first 11 to 13 weeks of pregnancy, and directly detected, and reported in 2 weeks; amniotic fluid was taken from 16 to 20 weeks in the second trimester, and tested after culture, and reported in 3 weeks
At present, there are many laboratories in China that can provide lysosomal enzyme detection, including Beijing Xiehe Hospital, Shanghai Xinhua Hospital, Beijing Institute of Traditional Chinese Medicine. Clinicians can recommend patients with lysosomal storage disease to the above hospitals for testing. In short, prenatal diagnosis is the only effective measure to prevent the birth of children, and it is also an important job to improve the quality of our population.
Lysosomal storage case diagnosis and prenatal diagnosis
(I) Overview: The lysosome is an organelle, that is, the ultrastructure inside the cell. It is a single-layer-coated vesicle with a lipoprotein membrane on the outside. It is a cell processing and recycling system. The internal liquid is acidic and contains more than 60 acid hydrolytic enzymes that can degrade various biological macromolecules, such as nucleic acids, proteins, lipids, mucopolysaccharides, and glycogen. The various biological macromolecules that make up a cell are in a dynamic equilibrium, constantly being decomposed and continuously re-synthesized. Biological macromolecules that are ingested through endocytosis also need to be broken down into different components before they can be used. These macromolecules are broken down in the lysosome.
Each enzyme in the lysosome has its own coding gene. Defects of each enzyme directly lead to the failure of a particular biological macromolecule to normally degrade and accumulate in the lysosome. The common result is that the lysosome swells, the cells become bloated and abnormal, and the cell function is severely affected, eventually leading to a disease called Lysosomal storage disease (LSD). The direct cause of the enzyme deficiency is a mutation in the coding gene, most of which are autosomal recessive, which is a group of more common genetic metabolic diseases. According to statistics, nearly 5 children per 10,000 newborns have this disease. There is no effective treatment. It has the largest proportion in the prenatal diagnosis of hereditary metabolic diseases. Therefore, prenatal diagnosis of high-risk pregnant women is the only effective measure to prevent the birth of children.
(B) Common characteristics of lysosomal enzymes:
1. Both are acid hydrolases and are mannose-containing glycoproteins. The optimum pH for enzyme action is 3.5 5.5. Lysosomes rely on the action of a proton pump to maintain an acidic environment (pH 5.0 to 5.5).
2. Is a telomerase. When the macromolecules in the lysosome are degraded, the enzyme removes the glycosyl, sulfate, lipid and acid residues one by one from the end of the macromolecule.
3. Exists in lysosomes in multiple forms. Most lysosomal enzymes exist in a soluble matrix, and no detergent is required in the experimental steps; a few are components of the lysosomal membrane (such as glucocerebrosidase, acid phosphatase), so it is necessary to use Detergent.
(Three) characteristics of lysosomal storage disease:
1. Most are autosomal recessive diseases. That is, both parents are heterozygous with normal phenotype, and the risk of developing children is one-fourth. More than 30 diseases have been identified.
2. Multiple tissues or organs are affected. The main clinical manifestations are mental retardation, skeletal and nervous system development disorders. Seriously affect the vitality of patients.
3. The clinical condition is progressively worsened. Diseases such as mucopolysaccharidosis, GM1 and GM2 ganglioside storage disorders, and metachromatic white matter dystrophy are manifested as a progressive increase in neurological damage.
4. The storage is covered by a single layer of lysosomal membrane.
5. Diversified storage composition.
6. Determination of enzyme activity is a reliable basis for the final diagnosis of the disease.
7. Some diseases can be treated with enzyme supplements. Such as Gaucher disease; there is no effective treatment for most diseases, but diagnosis and prenatal diagnosis can be made by measuring enzyme activity.
Due to the serious condition of lysosomal storage disease, there is no effective treatment for most diseases, and the prognosis is poor. The birth of a child brings a heavy economic and spiritual burden on society and the family. Although there is no effective treatment for this disease, most of them can clearly determine whether the fetus is sick before giving birth, and some can also make an antenatal diagnosis in the first trimester. Because it can prevent the fetus from being born in the clinic based on a clear prenatal diagnosis, it is not only the only feasible eugenic measure, but also can reduce the burden on the family and society and improve the quality of the population.
The types, classifications, and corresponding deficiencies of lysosomal storage diseases are listed in Table 1.
Table 1 Lysosomal storage disease and corresponding hydrolase deficiency
classification | Disease name | Defective hydrolase |
Sphingolipid storage disease | Metachromatic leukodystrophy | Aryl Sulfatase A (ASA) |
| White cell dystrophy | Galactocerebrosidase |
| GM1 Ganglioside Storage Syndrome | beta-galactosidase |
| black? Dementia (Tay-Sachs disease) | -aminohexosidase A |
| Sanhoff disease | -aminohexosidase A + B |
| Gaucher's disease | -glucosidase |
| Niemann-Pick disease | Sphingomyelinase |
| Fabry disease | -galactosidase |
| Farber disease | Ceramidase |
Glycogen storage disease | Glycogen storage disease type | alpha-glucosidase |
Glycoprotein storage disorder | Fucosin storage disease | Alpha-fucosidase |
| Adenosyl storage disease | alpha-glucosidase |
| Sialic acid storage disease | Sialidase |
| Aspartyl glucosamine | Aspartyl aminoglucosidase |
Mucopolysaccharidosis | MPS | -L-iduronidase |
| MPS | Iduronic acid sulfatase |
| MPSA | Heparin-N-sulfatase |
| MPSB | -N-acetylglucosidase |
| MPSC | Acetyl-CoA: alpha-glucosamine acetyltransferase |
| MPSD | N-acetylglucosamine-6-sulfatase |
| MPSIVA | Galactose-6-sulfatase |
| PMSB | -galactosidase |
| MPS | Arylsulfatase B (ASB) |
| MPS | beta-glucuronidase |
Mucolipid storage disease | ML and | Phosphotransferase deficiency causes multiple soluble Elevated enzymes |
Cholesterol ester storage disease | Wolman disease | Acid esterase |
(IV) Method for measuring lysosomal enzyme activity: The diagnosis of lysosomal storage disease is carried out by measuring enzyme activity or measuring metabolites. In the past, methods and procedures for measuring enzyme activity were relatively complicated, and the amount of substrate was large. After 1980, the Laboratory of Genetic Metabolic Diseases at the University of Erasmus in the Netherlands successfully applied a microenzyme assay. It uses a new synthetic substrate, which improves the sensitivity and accuracy of the experiment and simplifies the experimental steps. In 1990, the Laboratory of Medical Genetics, Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences introduced the laboratory's microenzyme assay method, and established 10 enzyme assay methods. Now, when performing the measurement of the above 10 kinds of enzyme activities in this room, the experiment originally performed in a test tube is changed to an Eppendroff tube, and various enzyme activity measurement methods are standardized. As a result, the experimental steps are simplified, the accuracy is improved, and the amount of added substrate and enzyme source can be accurately calculated. For example, melancholic dementia is caused by the lack of aminoglycosidase A (Hex A). In the past, the fluorescent substrate 4-methyl--DN-acetylglucosamine (4MUG) was used to measure the total activity of Hex before measuring Hex B activity was calculated, and Hex A activity was calculated from it. Currently, 4-methyl--DN-acetylglucosamine-6-sulfate (4MUGS) is used as a substrate, and Hex A activity can be directly measured. Another example is that MPS IV A is caused by galactose-6-sulfatase deficiency. In the past, isotopically labeled substrates were used, and now new fluorescent substrates are used, and the isotope labeling step is omitted. Except for arylsulfatase A and B, which are chromogenic substrates, other fluorescent substrates are used. Each enzyme activity determination method uses a uniform procedure, that is, 20 l of cell homogenate is added to 40 l of substrate, mixed thoroughly, placed in a 37 ° C water bath and incubated for 1 hour, then 400 l of 0.5 mol / L sodium carbonate and sodium bicarbonate buffer are added. Solution (pH 10.7), the reaction was terminated, and the enzyme activity was measured with a fluorescence spectrophotometer. The excitation wavelength was 365 m and the emission wavelength was 445 m. The improvement of the above methods has laid the foundation for villus removal in early pregnancy for prenatal diagnosis.
From 1991 to 1997, the Department of Medical Genetics of Xiehe Medical University conducted prenatal diagnosis of 28 high-risk pregnant women based on the diagnosis of 90 probands (Table 2), of which 14 were obtained by villus removal in early pregnancy. Five cases of diseased fetuses were detected, including two cases of mucopolysaccharidosis, one case of metachromatic leukodystrophy, and one of GM1 and GM2 ganglioside storage. The results of the new method were confirmed by amniotic fluid cells and postnatal fetal examination. The above practical results show the reliability of prenatal diagnosis in early pregnancy.
Table 2 Number of cases and prenatal diagnosis of lysosomal storage disease (1991 1997)
Disease name | Case diagnosis | Prenatal diagnosis |
Mucopolysaccharidosis | 45 | 9 |
Gaucher disease (Gaucher's disease) | 18 | 2 |
Metachromatic leukodystrophy | 10 | 5 |
Nieman-Pick disease | 3 | 4 |
Mucolipid storage disease | 6 | 3 |
GM1 Ganglioside Storage Syndrome | 2 | 3 |
GM2 Ganglioside Storage Syndrome | 4 | 2 |
White cell dystrophy | 2 |
|
total | 90 | 28 |
(5) Precautions for diagnosis: The prerequisite for prenatal diagnosis is to find out which enzyme defect the proband has. Doing this requires close cooperation between the clinic and the laboratory. An analysis of which enzyme deficiency disease is most likely to be made from clinical manifestations can be used to purposefully test that enzyme. Although the research on this group of diseases has reached the molecular level, the methods and steps are relatively complicated and take a long time. Therefore, genetic diagnosis cannot replace the position of enzyme activity measurement for prenatal diagnosis.
It is worth noting that the enzyme activity related to some cases is in the normal range, and the cause of the disease is the deficiency of the activating protein related to the enzyme activity, such as metachromatic leukodystrophy. In this case, prenatal diagnosis cannot be made by measuring enzyme activity.
For prenatal diagnosis, amniotic fluid can be taken from 17 to 20 weeks of second trimester to obtain amniotic fluid, and cultured amniotic fluid cells can be used for enzyme activity determination or 35S incorporation experiment. In recent years, villi can be taken for enzyme activity from 7 to 12 weeks in early pregnancy Assay, but cannot completely replace the amniotic fluid cell method. Because some enzymes are not expressed in the villi or are interfered by other factors in the villous specimen.
