Beta-mercaptolactate-cysteine disulfiduria. MCDU. Disulfiduria mixed.
Incidence
Autosomal recessive. Very rare.
Clinical Characteristics
Ampola et al. (1969) described a placid, hypokinetic, 45-year-old male, the product of brother-sister incest, who had a low IQ, grand mal seizures, flattened nasal bridge, and excessively arched palate. He was found in the course of screening mentally retarded patients with the nitroprusside test. He excreted large amounts of a sulfur-containing amino acid, shown by Crawhall et al. (1969) to be beta-mercaptolactate-cysteine disulfide. The structure of the disulfide is indicated by its name: in one-half of the molecule the-NH2 of cysteine is replaced by-OH. Administration of cysteine, but not of methionine, increased excretion of the mixed disulfide (Crawhall et al., 1971). During a screening for cystinuria in the regular schools, Niederwieser et al. (1973) found the same material in the urine of 2 mentally normal sisters, aged 11 and 13 years. In Sweden, Hannestad et al. (1981) detected MCDU in a mentally retarded woman. Her red cells were devoid of activity of the enzyme mercaptopyruvate sulfurtransferase (MST). Both parents and 5 other relatives in a pattern consistent with their being heterozygotes showed intermediate levels of red cell MST. The presumed heterozygotes also excreted excessive amounts of mercaptolactate and mercaptoacetate in the urine.
Precipitants
None
Provocation Tests
Administration of cysteine, but not of methionine, increased excretion of the mixed disulfide.
Diagnostic Procedures
EB-R. Mercaptopyruvate sulfurtransferase (MST) deficiency in red cells. Aminoacids in urine quantitative.