• Confirm biotinidase deficiency in infants identified by newborn screening (activity assay)

• Identify causative mutations (mutation assay)

• Identify biotinidase deficiency carriers (mutation assay)

• Prenatal diagnosis of biotinidase deficiency (mutation assay)

Biotinidase deficiency is an autosomal recessive disorder characterized by central nervous system and skin manifestations. Individuals with profound deficiency usually present around 3 months of age, but may present as early as the first week of life and as late as 10 years of age. If untreated, the patient may experience seizures, developmental delay, skin lesions, and irreversible sensorineural deafness. Individuals with partial deficiency may have milder symptoms or may be asymptomatic. Patients are treated successfully with oral doses of free biotin, a water-soluble form of vitamin B.

Biotin is routinely recycled in the body when the enzyme biotinidase liberates biotin from endogenous and dietary proteins. Biotin acts as a coenzyme in gluconeogenesis, fatty acid synthesis, and branched chain amino acid catabolism. Biotinidase deficiency diminishes or prevents biotin recycling and coenzyme function. Thus, affected individuals may have ketolactic acidosis, organic aciduria, and mild hyperammonemia.

Biotinidase deficiency is detected via newborn screening (colorimetric, semiquantitative assessment of biotinidase activity) and follow-up quantitative measurement of biotinidase activity. BTD gene analysis can identify the causative mutation(s), of which there are about 100; identify carriers of a mutated gene (1:120 frequency in the general population); and diagnose the deficiency prenatally. Use of these laboratory tests enables early detection, which can lead to prevention of reversible and irreversible symptoms.

Biotinidase Activity

• Enzymatic method that reports in nmol/mL/min

Mutation Analysis

• Polymerase chain reaction (PCR) amplification of the entire coding region, splice junction sites, and promoter region of the biotinidase gene followed by dye-terminator sequencing of the PCR products and automated capillary electrophoresis

Biotinidase Activity with Reflex to Mutation Analysis

• See individual assays

Biotinidase Activity

Low levels are consistent with biotinidase deficiency.

Mutation Analysis

The presence of 2 deleterious mutations is consistent with a biotinidase deficiency diagnosis, while the presence of 1 deleterious mutation indicates at least a carrier status. Absence of deleterious mutations suggests the patient is neither affected nor a carrier of biotinidase deficiency.