The biotinidase activity test is a specialized biochemical analysis used to evaluate the enzymatic activity of biotinidase, an essential enzyme responsible for recycling biotin (vitamin B7) from dietary and endogenous protein-bound forms. The test is primarily used to screen for or confirm biotinidase deficiency, a rare inherited metabolic disorder that can result in severe neurological and dermatological symptoms if left undiagnosed. It is typically performed in newborns as part of expanded metabolic screening, but can also be helpful in older individuals presenting with unexplained neurological symptoms or metabolic acidosis.
Biotinidase is essential for maintaining biotin balance by cleaving biotin from biocytin and other biotinyl-peptides, enabling the vitamin to be reused in vital cellular functions. Biotin serves as a coenzyme for several carboxylases involved in gluconeogenesis, fatty acid synthesis, and the breakdown of amino acids. When biotinidase activity is deficient or absent, biotin recycling is disrupted, leading to a functional biotin deficiency even if dietary intake is sufficient. This enzyme deficiency results in decreased activity of biotin-dependent enzymes, triggering a series of metabolic problems.
When biotinidase activity is significantly lower than normal, it indicates either partial or profound biotinidase deficiency, depending on the level of residual enzyme activity. Profound deficiency is linked to symptoms such as developmental delay, seizures, hypotonia, ataxia, hearing loss, skin rash, and alopecia. Partial deficiency may present with milder or intermittent symptoms and can become clinically significant under stressful conditions, such as illness or fasting. Early detection through this test enables prompt biotin supplementation, which can prevent the onset of symptoms and metabolic crises.
Higher-than-expected biotinidase activity is not typically associated with pathological states and may occur rarely due to increased enzyme induction.
See also: Biotinidase Deficiency, Genetic Testing
