Acute hereditary tyrosinaemia type I: clinical, biochemical and haematological studies in twins.

Affected twins with acute hereditary tyrosinaemia type I are described. Attempts at therapy with a phenylalanine-tyrosine-methionine restricted diet supplemented with cysteine, vitamin E and ascorbic acid failed to influence the course of the disorder. The bleeding diathesis was due to a morbid reduction of a number of clotting factors, particularly factor VII, and this was associated with impaired platelet aggregation and release. The liver of one showed a marked reduction in fumarylacetoacetate lyase activity and her urine contained a potent inhibitor of red cell delta-aminolaevulinic acid dehydratase. Biochemical investigations of cultured fibroblasts suggest that these do not express the disorder and are unlikely to prove useful diagnostically.