Late‐onset holocarboxylase synthetase deficiency

Summary We report a 21‐month‐old female patient whose urine organic acid profile suggested a biotin utilization abnormality consistent with multiple carboxylase deficiency. For most previously reported patients, holocarboxylase synthetase deficiency has correlated with the early‐onset variant of multiple carboxylase deficiency; conversely, biotinidase deficiency has been characteristic of the late‐onset form. In vitro enzyme studies revealed that our patient suffered from holocarboxylase synthetase deficiency. We suggest that holocarboxylase synthetase deficiency should be considered in the differential diagnosis of older patients in whom there is suspicion of a defect in biotin metabolism.