There are two genetically determined
biotin-dependent disorders. The first is holocarboxylase
synthetase (HCS) deficiency and the second
biotinidase deficiency. HCS catalyzes the reaction in which active holocarboxylases are synthesized from inactive apocarboxylases.
Biotin is required for this synthesis.
Biotinidase facilitates the release and recycling of free
biotin. Deficiency of either HCS or
biotinidase is characterized by certain neurological, cutaneous and biochemical abnormalities. In this paper, six patients with
biotinidase and two patients with HCS deficiency are described. Among the most common neurological findings were
hypotonia (6/8),
seizures (2/6) and
optic atrophy (2/8).
Dermatitis and
conjunctivitis were present in three and four patients, respectively. All patients had low blood pH
bicarbonate levels. Serum
lactate was increased in all and
pyruvate in six cases. Two patients with
biotinidase deficiency presented earlier than the mean age of onset previously reported in the literature. Detection of eight cases during the past few years at a single metabolic unit indicates that
biotinidase deficiency is not rare in Turkey, where the frequency of some other metabolic disorders has also been reported to be high. We suggest that
biotin-dependent disorders should be considered in all infants with neurological symptoms, particularly those with jerks, even if other signs such as
alopecia,
seborrheic dermatitis and
acidosis are not evident, regardless of the age of presentation.