Biotinidase deficiency is an autosomal recessive disoder caused by mutations in the biotinidase gene. Age of onset and clinical phenotype vary depending on the amount of residual Biotinidase activity. The combined incidence of profound and partial Biotinidase deficiency is 1 in 61000. The carrier frequency in the general population is 1 in 120. This assay is used for diagnosing biotinidase deficiency. It is also useful for follow up testing for certain Organic acidurias.