Biotinidase deficiency is an autosomal recessively inherited disorder that results in the inability to recycle the vitamin biotin. 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 BTD gene provides instructions for making an enzyme called biotinidase. This enzyme helps the body reuse biotin, a B vitamin found in foods such as liver, egg yolks, and milk. Biotinidase removes biotin that is bound to proteins in food, leaving the vitamin in its free state. The body needs free biotin to break down fats, proteins, and carbohydrates effectively. Biotinidase also recycles biotin within the body.
Mutations in the BTD gene reduce or eliminate the activity of biotinidase. Profound biotinidase deficiency results when the activity of biotinidase is reduced to less than 10 percent of normal. Partial biotinidase deficiency occurs when biotinidase activity is reduced to between 10 percent and 30 percent of normal. Without enough of this enzyme, biotin cannot be separated from proteins or recycled normally. As a result, the body is less able to process important nutrients. These defects underlie the potentially serious medical problems associated with biotinidase deficiency.
Direct sequencing of BTD, the only gene known to be associated with biotinidase deficiency, can be performed by our laboratory. Detection frequency ~99%
Methodology: Sequencing of entire coding region
Purpose: Confirmation of Clinical Diagnosis
ICD-10 Code D84.1
Test Requisition: Sequencing Requisition
CPT Code: 81404 Cost: $863.00
Turn-around-time: 3-4 weeks
1. McMahon RJ.(2002) “Biotin in metabolism and molecular biology”. Annu Rev Nutr. 22:221-39.
2. Weber P, Scholl S, Baumgartner ER. (2004) “Outcome in patients with profound biotinidase deficiency: relevance of newborn screening”. Dev Med Child Neurol. 46(7):481-4.
3. Wolf B. (2005) “Biotinidase: its role in biotinidase deficiency and biotin metabolism”. J Nutr Biochem. 16(7):441-5.