Biotinidase deficiency is an autosomal recessive inherited metabolic disease caused by pathogenic variants in the BTD gene. The enzyme biotinidase is involved in the recycling of unbound biotin and thus in maintaining biotin-dependent metabolic processes. Decreased enzyme activity results in reduced levels of biotin, which is required as a co-factor for certain carboxylases. Therefore, the symptoms of BTD deficiency are similar to biotin deficiency with neurological and dermal manifestations.
The disease is classified according to the degree of severity based on the residual enzyme activity. Partial biotinidase deficiency usually remains asymptomatic even if untreated.
- very severe biotinidase deficiency: residual enzyme activity < 1%
- severe biotinidase deficiency: residual enzyme activity between 1 and 10%
- partial biotinidase deficiency: enzyme residual activity between 10 and 30%
The diagnosis of BTD deficiency is part of newborn screening. In case of conspicuous findings, the diagnosis can be confirmed by molecular genetics. Due to early detection and therapy with lifelong oral biotin supplements, the prognosis of the disease is positive.
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