A review of the clinical presentation and laboratory findings in two uncommon hereditary disorders of sulfur amino acid metabolism, beta-mercaptolactate cysteine disulfideuria and sulfite oxidase deficiency.

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Two hereditary disorders of sulfur amino acid metabolism , beta -mercaptolactate-cysteine disulfideuria and sulfite oxidase deficiency , were described twenty years ago . Other examples of these disorders have been limited to about 5 of each in the world literature since then . Reasons for the apparent rarity of these conditions are discussed and the analytical procedures to identify them are reviewed . The detection of the first depends on the positive result of a cyanide-nitroprusside test followed by positive identification of the specific mixed disulfide . The enzyme mercaptopyruvate sulfur transferase has been shown to be deficient . In the second disorder of sulfite oxidase deficiency , the clinical presentation with progressive dystonia and dislocated lenses in an infant should suggest further laboratory investigations for this disorder which would not be detected by conventional laboratory screening procedures . Laboratory diagnosis can be obtained by use of the Merckoquant sulfite test on a fresh urine sample . Quantitative thiosulfate and taurine measurements can also be made . Positive identification of the specific amino acid S-sulfo-L-cysteine should also be made . The enzyme sulfite oxidase is missing from such organs as liver , kidney and brain . This latter condition may also be associated with xanthinuria . For this combined disorder of sulfite oxidase and xanthine oxidase , a deficiency of a molybdenum-containing cofactor has been demonstrated .