Congenital defects in the enzymes responsible for the degradation of proteoglycans lead to disorders in proteoglycan catabolism, resulting in various types of mucopolysaccharidoses. These conditions are characterized by the excessive accumulation and excretion of oligosaccharides. While the metabolic basis of different types of mucopolysaccharidoses is similar, their genetic patterns and clinical manifestations vary.

bubble_chart Etiology

Mucopolysaccharidosis abdominal mass disease is caused by congenital defects in lysosomal acid hydrolases. Based on disease cause, this condition can currently be divided into eight major types. Over 200 cases have been reported in China, primarily presenting with severe skeletal deformities, hepatosplenomegaly, intellectual disabilities, and other malformations. For mucopolysaccharidosis abdominal mass disease, prenatal diagnosis is most reliably achieved by measuring specific enzyme activity in cultured amniotic fluid cells. However, this method has high experimental requirements and is difficult to perform in general laboratories. Two simpler and practical methods are toluidine blue qualitative testing and uronic acid semi-quantitative measurement.

1. Toluidine blue qualitative test: The method is the same as that used for urinary mucopolysaccharide testing. In early pregnancy, normal amniotic fluid may test positive, whereas in the late stage [third stage] of pregnancy, a negative result is expected. A positive result suggests that the fetus has mucopolysaccharidosis abdominal mass disease.
2. Uronic acid semi-quantitative measurement: Acidic mucopolysaccharides in amniotic fluid react with a sodium tetraborate sulfuric acid solution to form uronic acid. The amount of uronic acid per milligram of creatinine reflects the quantity of acidic mucopolysaccharides. As pregnancy progresses, uronic acid levels gradually decrease. The reference value for weeks 16–20 of pregnancy is 3.3–7.0 mg/mgCr. Values above this range should raise suspicion of mucopolysaccharidosis. This method is diagnostically significant for all types of mucopolysaccharidosis abdominal mass disease except for Morquio syndrome.

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The pathogenic gene is located on an autosome, and the gene trait is recessive, meaning symptoms only manifest in homozygotes. In this type of genetic disorder, both parents are carriers of the pathogenic gene, so it is more common in the offspring of consanguineous marriages. There is a 1/4 probability of the offspring being affected, with equal chances for sons and daughters. Many inherited metabolic disorders fall under autosomal recessive inheritance. According to the "one gene, one enzyme" or "one cistron, one polypeptide" concept, abnormalities in the enzymes or protein molecules in these metabolic disorders stem from mutations in their respective encoding genes. Common autosomal recessive disorders include lysosomal storage diseases such as glycogen storage disease, lipid storage disease, and mucopolysaccharidosis; defects in synthase activity like agammaglobulinemia and albinism; as well as phenylketonuria, Wilson's disease, and galactosemia.

bubble_chart Clinical Manifestations

1. Mucopolysaccharidosis type I (MPS I): Also known as Hurler syndrome or Cheng-Lei disease. AR. Caused by deficiency of the lysosomal enzyme alpha-L-iduronidase, with an incidence of 1 in 100,000 newborns. Main features: progressive developmental delay, short stature, intellectual disability, scaphocephaly, short neck, coarse facial features, corneal clouding, joint stiffness, limited mobility, and kyphosis. Others: retinal pigmentation, deafness, thoracic deformity, hepatosplenomegaly, enlarged abdomen, heart valve defects, and arterial pulse hardening. Positive mucopolysaccharide screening; carriers can be detected by enzyme activity assay. Poor prognosis, with most patients dying in childhood.
2. Mucopolysaccharidosis type II (MPS II): Also known as Hunter syndrome. XR, no female patients, with an incidence of 6 in 100,000. Caused by deficiency of iduronate sulfatase. Main features: similar to type I but without corneal clouding or kyphosis. Others: hirsutism, progressive deafness; muscle rigidity and spasms, impulsive behavior. Two-thirds of patients develop seizures after age 10. Diagnosis and differentiation are similar to type I, primarily based on clinical manifestations. Severe cases often die before adolescence.