| Description: |
Biotin is the essential coenzyme for four biotin-dependent carboxylases in humans: pyruvate carboxylase, propionyl CoA carboxylase, b -methylcrotonyl CoA carboxylase, and acetyl CoA carboxylase. These enzymes have important roles in gluconeogenesis, fatty acid synthesis, and amino acid catabolism. Biotinidase deficiency (MIM 253260), also known as late-onset (juvenile) multiple carboxylase deficiency, is a disorder of biotin recycling. In the untreated state, profound biotinidase deficiency is usually initially characterized by seizures, hypotonia, ataxia, developmental delay, vision problems, hearing loss, and cutaneous abnormalities such as alopecia, skin rash, and tendency to fungi infection. With age, motor limb weakness, spastic paresis, and decreased visual acuity occur. Individuals with partial biotinidase deficiency may have hypotonia, skin rash, and hair loss, particularly during times of stress. Biotinidase deficiency can be diagnosed by demonstrating deficient enzyme activity in serum. BTD gene sequencing is most useful when the results of enzymatic testing are ambiguous, such as in differentiating profound biotinidase deficiency from partial biotinidase deficiency or heterozygous carriers. BTD1 gene maps to chromosome 3p25.1. It contains 4 coding exons, and encodes for a protein of 543 amino acids.
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