[Molecular basis of vitamin-responsive inborn errors of metabolism].

In inborn errors where the defective enzyme had a cofactor requirement it was found that the administration of large amounts of the vitamin resulted in a clinical and biochemical improvement. A mutation that imposes an exaggerated requirement for a vitamin affects the apoenzyme directly, the conversion of a vitamin into coenzyme, or the attachment of vitamin to the apoenzyme. Direct proof has so far been provided that molecular defects in the said gene underlie both the vitamin-responsive and vitamin-nonresponsive forms. HCS deficiency is an exception, all HCS-deficient patients being responsive to biotin administration. We examined the relationship between the kinetic characteristics of HCS mutants and the clinical and biochemical features of the HCS deficient patients.