Biotinidase deficiency is an autosomal recessive disorder of biotin recycling with an estimated incidence of 1:60,000. Deficiency of the biotinidase enzyme will result in decreased levels of free biotin, impairing the activity of multiple biotin-dependent enzymes. If untreated, patients with profound biotinidase deficiency may exhibit seizures, hypotonia, ataxia, developmental delay, vision problems, hearing loss, and cutaneous abnormalities such as alopecia, skin rash, and candidiasis. With age, motor limb weakness, spastic paresis, and decreased visual acuity occur. Once vision problems, hearing loss, and developmental delay occur, they are usually irreversible even with biotin therapy. Untreated patients with partial biotinidase deficiency may have hypotonia, skin rash, and hair loss, particularly during times of stress.