Newborn screening · Other inherited disorder
Biotinidase Deficiency · BIOT
Treated with oral biotin. Untreated, it causes neurologic damage. One of the cleanest screening wins.
Description
Biotinidase deficiency is an autosomal recessive disorder of biotin recycling. Biotinidase, encoded by BTD on chromosome 3, cleaves biocytin and biotinyl-peptides released during protein turnover, freeing biotin for reuse as a cofactor for the four human carboxylases that participate in fatty acid synthesis, gluconeogenesis, and amino acid catabolism. Loss of biotinidase activity drains the body's biotin pool over months as dietary biotin alone cannot match the demand.
Two clinical forms are distinguished by residual enzyme activity. Profound biotinidase deficiency is defined as less than 10 percent of mean normal serum biotinidase activity. Partial deficiency is defined as 10 to 30 percent of mean normal activity. Untreated profound deficiency typically presents in the first months of life with seizures, hypotonia, ataxia, alopecia, eczematous skin rash, recurrent fungal or bacterial infections, metabolic acidosis, and developmental delay. Sensorineural hearing loss and optic atrophy can develop and may not fully reverse with treatment, which is the central reason newborn screening matters. Untreated partial deficiency can present during illness or other periods of metabolic stress with milder versions of the same features.
Detection is by newborn screening on the dried blood spot using a colorimetric or fluorometric biotinidase activity assay. Confirmation uses quantitative serum biotinidase activity and BTD gene sequencing. Reported live-birth incidence in pooled international newborn screening data is approximately 1 in 60,000 for profound deficiency and 1 in 30,000 to 1 in 40,000 for partial deficiency, with combined rates near 1 in 20,000. Wolf, Genetics in Medicine, 2012, summarized the natural history and screening literature. Founder populations including parts of Saudi Arabia and Türkiye report higher incidence linked to consanguinity.
Treatments to date
Treatment is oral biotin, also called vitamin B7, taken lifelong. Standard dosing for profound deficiency is 5 to 10 mg of free biotin per day. Partial deficiency is generally treated with 1 to 5 mg per day, sometimes only during periods of illness or metabolic stress, depending on the clinical and biochemical picture. Treatment is begun at the time of newborn screening confirmation, often within the first weeks of life, and is continued through adulthood and pregnancy.
There is no FDA-approved disease-specific drug for biotinidase deficiency because biotin is sold over the counter as a dietary supplement and is not regulated as a prescription medication. Pharmacy-grade biotin from a compounding pharmacy is used by many metabolic centers to ensure dose accuracy, since over-the-counter biotin products vary in actual content.
Biochemical normalization is rapid. Acidosis, rashes, alopecia, and seizures resolve within days to weeks of starting treatment in most newborns identified by screening. Hearing loss and optic atrophy that developed before treatment may not reverse and are the dominant residual deficits in cohorts of children diagnosed clinically rather than by screening. A metabolic geneticist or biochemical genetics clinic typically manages follow-up, with periodic confirmation of compliance and adjustment of dose during pregnancy or growth. Early case series from Wolf and colleagues established that lifelong biotin supplementation prevents the irreversible neurologic and sensory complications of profound deficiency.