Institute of Genomic Medicine
Biotinidase Deficiency
BACKGROUND:
Biotinidase is an aminohydrolase that cleaves biotin from small biotinylated peptides and biocytin, thereby recycling the vitamin. Biotinidase activity can be detected using a colorimetric assay, identifying biotinidase deficient individuals and those heterozygous for enzyme deficiency.
INDICATIONS FOR TESTING:
Biotinidase deficiency (late-onset or juvenile multiple carboxylase deficiency) is an autosomal recessive disorder. Patients who are untreated become biotin depleted and develop secondary deficiencies of the biotin-dependent carboxylases. Children with profound deficiency may exhibit seizures, hypotonia, alopecia, skin rash, hearing loss, developmental delay, keto-acidosis, lactic acidosis, and organic aciduria. Those with partial deficiency may develop symptoms with intercurrent infections or dietary restriction of biotin.
PROCEDURE:
Quantitation of biotinidase activity can be accomplished by using a simple colorimetric enzyme assay. Biotinidase cleaves the amide bond of biotinyl-p-aminobenzoic acid (B-p-ABA), resulting in free biotin and p-aminobenzoate (p-ABA). The p-ABA is then diazotized and coupled to a naphthol reagent, producing a purple product that can be quantitated spectrophotometrically. In the absence of biotinidase activity, product is not formed and color development does not occur.>
SAMPLE REQUIREMENTS
Serum:
2cc of blood drawn in a red top vacutainer tube. Specimen should be spun down immediately and stored at -70°C to avoid loss of activity.
INTERPRETATION:
Patient's results are compared to a reference range of normal adult values. Values less than 10% of normal adult activity are considered biotinidase deficient. Values 10-30% of normal adult values are considered partially biotinidase deficient. Neonates and infants less than 6 months of age usually have activities lower than that of normal adults. Sulfonamide therapy can interfere with this test.
