Emeritus Chairman, Department of Medical Genetics Henry Ford Hospital Attending Physician at Children’s Hospital of Michigan Professor, Center for Molecular Medicine and Genetics Wayne State University School of Medicine Detroit, Michigan
Initial Posting: March 24, 2000; Last Update: June 9, 2016.
If untreated, young children with profound biotinidase deficiency usually exhibit neurologic abnormalities including seizures, hypotonia, ataxia, developmental delay, vision problems, hearing loss, and cutaneous abnormalities (e.g., alopecia, skin rash, candidiasis). Older children and adolescents with profound biotinidase deficiency often exhibit motor limb weakness, spastic paresis, and decreased visual acuity. Once vision problems, hearing loss, and developmental delay occur, they are usually irreversible, even with biotin therapy. Individuals with partial biotinidase deficiency may have hypotonia, skin rash, and hair loss, particularly during times of stress.
The diagnosis of biotinidase deficiency is established in a proband whose newborn screening or biochemical findings indicate multiple carboxylase deficiency based on either detection of deficient biotinidase enzyme activity in serum/plasma OR identification of biallelic pathogenic variants in BTD on molecular genetic testing.
Treatment of manifestations: All symptomatic children with profound biotinidase deficiency improve when treated with 5-10 mg of oral biotin per day. All individuals with profound biotinidase deficiency, even those who have some residual enzymatic activity, should have lifelong treatment with biotin. Children with vision problems may benefit from vision aids; those with hearing loss will usually benefit from hearing aids or cochlear implants, and those with developmental deficits from appropriate interventions.
Prevention of primary manifestations: Children with biotinidase deficiency identified by newborn screening should remain asymptomatic if biotin therapy is instituted early and continuously lifelong.
Surveillance: Annual vision and hearing evaluation, physical examination, and periodic assessment by a metabolic specialist.
Agents/circumstances to avoid: Raw eggs because they contain avidin, an egg-white protein that binds biotin and decreases the bioavailability of the vitamin.
Evaluation of relatives at risk: Testing of asymptomatic sibs of a proband ensures that biotin therapy for affected sibs can be instituted in a timely manner.
Biotinidase deficiency is inherited in an autosomal recessive manner. With each pregnancy, a couple who has had one affected child has a 25% chance of having an affected child, a 50% chance of having a child who is an asymptomatic carrier, and a 25% chance of having an unaffected child who is not a carrier. Carrier testing for at-risk family members and prenatal testing for pregnancies at increased risk are options if the pathogenic variants in the family are known.