ABSTRACT
Biotinidase deficiency is a form of multiple carboxylase deficiency in which the fundamental defect is an inability to cleave biocytin (Figures 6.1 and 6.2), and this leads to defective activity of propionylCoA carboxylase, 3-methylcrotonylCoA carboxylase and pyruvate carboxylase [1]. Multiple carboxylase deficiency is also caused by defective activity of holocarboxylase synthetase [2] (Chapter 5). In earlier literature biotinidase deficiency was referred to as the later infantile form of multiple carboxylase deficiency [1,3] to distinguish it from the usual neonatal presentation of holocarboxylase synthetase deficiency. However, it is now clear that the latter disorder can present later and the former earlier; the way to distinguish them unambiguously is by enzyme analysis.
