beta-Mannosidase deficiency was demonstrated in fibroblasts of a girl who showed severe psychomotor retardation, bone deformities and gargoylism and recurrent skin and respiratory infections and who died at 20 years of age from bronchopneumonia. This first demonstration of a female patient confirms the autosomal recessive inheritance of beta-mannosidosis. Further investigation of this gypsy family revealed beta-mannosidosis in an older brother with a milder manifestation of gargoyl facial dysmorphology, mental retardation, hearing impairment and recurrent infections. beta-Mannosidase activity was completely deficient in his cultured skin fibroblasts, leukocytes and plasma. In urine a characteristic disaccharide was present. Heterozygote levels of beta-mannosidase were found in fibroblasts and/or plasma of the parents and one sister.
Fibroblasts from patients with Morquio B syndrome contain normal numbers of beta-galactosidase molecules with normal turnover but strongly reduced activity per enzyme molecule. Various substrate affinities are abnormal: the Km for methylum belliferyl (MU)-beta-galactoside is 4-10-fold elevated and affinity for keratan sulphate and oligosaccharides, isolated from Morquio B urine, was not detectable. In contrast, these substrate affinities are normal for beta-galactosidase in adult type GM1-gangliosidosis fibroblasts. Cell hybridization studies demonstrate that Morquio B syndrome and infantile and adult type GM1-gangliosidosis belong to the same complementation group. From these results we conclude that Morquio B syndrome is caused by a mutation in the structural gene for beta-galactosidase, which is allelic to the mutations in infantile and adult type GM1-gangliosidosis. Urinary excretion of keratan sulphate and oligosaccharides is abnormal in Morquio B syndrome but normal in adult type GM1-gangliosidosis. The catalytic properties of beta-galactosidase in Morquio B syndrome and GM1-gangliosidosis provide a possible explanation for the distinct clinical manifestations in these disorders.
In a patient with methylmalonic acidaemia (MMAA), persistent neurological symptoms were observed in addition to the acute episodes of metabolic dysequilibrium. CT scan and magnetic resonance imaging revealed bilateral symmetrical necrosis of the globus pallidus. Different episodes of metabolic decompensation, one with severe acidosis, had occurred. Persistent neurological symptoms in patients with MMAA who are appropriately treated suggest irreversible brain damage which appears to occur preferentially at the level of the basal ganglia.
Summary. Disorders of amino acid metabolism or transport are most clearly expressed in urine. Nevertheless the interpretation of abnormalities in urinary amino acid excretion remains difficult. An increase or decrease of almost every amino acid in urine can be due to various etiology. To differentiate between primary and secondary aminoacido-pathies systematic laboratory investigation is necessary. Early diagnosis of disorders of amino acid metabolism or transport is very important, because most of them can be treated, leading to the prevention of (further) clinical abnormalities. In those disorders, which cannot be treated, early diagnosis in an index-patient may prevent the birth of other siblings by means of genetic counseling and prenatal diagnosis.Primary aminoacidopathies can be due to genetically determined transport disorders and enzyme deficiencies in amino acid metabolism or degradation. Secondary aminoacidopathies are the result of abnormal or deficient nutrition, intestinal dysfunction, organ pathology or other metabolic diseases like organic acidurias.A survey of amino acid metabolism and transport abnormalities will be given, illustrated with metabolic pathways and characteristic abnormal amino acid chromatograms.
A new lysosomal storage disease with autosomal recessive inheritance is described in two male siblings of 5 1/2 and 4 years of age. Clinical manifestations started after 9 months of age with neurological symptoms, followed by progressive psychomotor deterioration. Urinary oligosaccharide excretion was abnormal and showed a characteristic pattern on chromatography. Enzyme assays showed a profound deficiency of lysosomal alpha-N-acetylgalactosaminidase in cultured fibroblasts, leukocytes and plasma from the patients and reduced activity in material from the parents. The deficiency was demonstrated both with an artificial substrate and a natural one, the blood group A trisaccharide. Excessive intra-lysosomal storage of alpha-N-acetylgalactosamine-containing material was demonstrated in cultured fibroblasts from the patients, using the lectin from Helix pomatia which is specific for terminal alpha-N-acetylgalactosamine residues.
In three pregnancies at risk for citrullinemia affected fetuses were predicted both by strongly increased levels of citrulline in the amniotic fluid and by the reduced incorporation of 14C-citrulline into TCA-precipitable material in cultured amniotic fluid cells. The prenatal diagnoses of affected fetuses were confirmed after termination of the pregnancies by direct and indirect assays of argininosuccinate synthetase in the fetal livers and fibroblasts respectively. Measurement of the citrulline concentration in amniotic fluid appears to be a valuable adjunct in the prenatal diagnosis of citrullinemia.
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