Recent advances in the prenatal diagnosis of the mucopolysaccharidoses

Cutaneous Manifestations of Mucopolysaccharidoses

Mucopolysaccharidoses (MPSs) are a group of inherited lysosomal storage disorders characterized by deficiencies in specific enzymes involved in the catabolism of glycosaminoglycans (GAGs). These deficiencies cause excessive metabolites to accumulate in multiple organs. There are eight different MPS disorders, contributing to the wide variation in clinical presentation. Depending on the severity and subtype of the disease, some children live normal life spans, while others have a more grim prognosis. Children with MPS can present with neurologic, behavioral, skeletal, cardiovascular, gastrointestinal, or respiratory abnormalities. Cutaneous manifestations are mostly nonspecific and can include coarse facial features, thickened skin, and excessive hair growth. More specific skin findings include ivory-colored "pebbly" papules found in Hunter syndrome and extensive dermal melanocytosis found in Hurler and Hunter syndromes. Early diagnosis of MPS disorders is extremely important to minimize the progression of the disease and for early initiation of appropriate treatment.

Inborn Errors of Metabolism

Inborn errors of metabolism are single gene disorders resulting from the defects in the biochemical pathways of the body. Although these disorders are individually rare, collectively they account for a significant portion of childhood disability and deaths. Most of the disorders are inherited as autosomal recessive whereas autosomal dominant and X-linked disorders are also present. The clinical signs and symptoms arise from the accumulation of the toxic substrate, deficiency of the product, or both. Depending on the residual activity of the deficient enzyme, the initiation of the clinical picture may vary starting from the newborn period up until adulthood. Hundreds of disorders have been described until now and there has been a considerable clinical overlap between certain inborn errors. Resulting from this fact, the definite diagnosis of inborn errors depends on enzyme assays or genetic tests. Especially during the recent years, significant achievements have been gained for the biochemical and genetic diagnosis of inborn errors. Techniques such as tandem mass spectrometry and gas chromatography for biochemical diagnosis and microarrays and next-generation sequencing for the genetic diagnosis have enabled rapid and accurate diagnosis. The achievements for the diagnosis also enabled newborn screening and prenatal diagnosis. Parallel to the development the diagnostic methods; significant progress has also been obtained for the treatment. Treatment approaches such as special diets, enzyme replacement therapy, substrate inhibition, and organ transplantation have been widely used. It is obvious that by the help of the preclinical and clinical research carried out for inborn errors, better diagnostic methods and better treatment approaches will high likely be available.

Amniotic fluid for screening of lysosomal storage diseases presenting in utero (mainly as non-immune hydrops fetalis)

Seventy amniotic fluids (AF) were sampled because of abnormal ultrasound findings (mainly non-immune hydrops fetalis (54 cases) or of the presence of vacuolated lymphocytes in fetal blood (3 cases)). They were analysed by a procedure involving AF supernatant analysis (glycosaminoglycans, oligosaccharides, free sialic acid and acid hydrolase activities) and biochemical study of cultured AF cells. Ten cases of lysosomal storage diseases (LSD) were diagnosed. The reported procedure allows an orientating screening within 3 days by analysis of 15 ml of third trimester AF supernatant (except for Gaucher and Niemann-Pick diseases). In some cases, the results allow an LSD diagnosis and a medical abortion without waiting for the formal diagnosis (in cultured AF cells that needs 3 more weeks), considering the poor prognosis of these LSD presenting in utero. Furthermore, the formal assessment of the diagnosis in the cultured fetal cells allows accurate genetic counselling for the couple.