Biotin‐responsive multiple carboxylase deficiency in an 8‐year‐old boy with normal serum biotinidase and fibroblast holocarboxylase‐synthetase activities

Summary An 8‐year‐old boy with late onset multiple carboxylase deficiency is described. Biotinidase deficiency and holocarboxylase‐synthetase deficiency have been excluded. A very slow biochemical response to biotin was found. The decrease in urinary organic acid excretion followed first‐order kinetics with a half‐life of about 50 days. The initially low carboxylase activities in thrombocytes were increased but not normalized after 3 months of treatment.