Division of Chemistry and Toxicology
	Biotinidase Deficiency Unit

		The enzyme biotinidase catalyzes the separation of the vitamin biotin from dietary sources of protein-bound biotin and from biotin complexed in carboxylase enzymes vital to the biotin metabolic cycle. A biotinidase-deficient infant cannot convert bound biotin to the free form needed for normal biotin cycle function; such a baby suffers from various physical and neurological disorders, such as seizures, hypotonia, alopecia, rashes and hearing loss. Treatment simply consists of a daily dose of biotin as a vitamin supplement.

 

	The Principles of the Test
		The biotinidase test uses a synthetic biotin substrate N-biotinyl-p-aminobenzoate (B-PABA). The blood of a normal newborn contains biotinidase and, in the assay, clears the substrate to biotin and P-aminobenzoic acid (PABA). After overnight reactions of the specimen with the substrate, a clear solution is obtained by precipitation of hemoglobin proteins with strong trichloroacetic acid.  Reagents are added in a timed sequence and purple color develops via a diazotization reaction of the amino groups from PABA and N-(1-naphthyl) ethylenediamine.   Pale or straw color remains with the blood of a biotinidase deficient newborn because the B-PABA substrate cannot be cleared to yield PABA. Marilyn Boucher, C (ASCP), Unit Manager Phone: 517-335-9795 boucherm@state.mi.us