Biotin dependency due to a defect in biotin transport

Area of Science:

• Biochemistry
• Genetics
• Metabolic Disorders

Background:

• Biotin dependency can arise from various genetic defects affecting biotin metabolism.
• Common causes include biotinidase deficiency, holocarboxylase synthetase deficiency, and nutritional biotin deficiency.

Observation:

• A 3-year-old boy presented with acute encephalopathy and carboxylase deficiencies, responsive to biotin supplementation.
• Standard genetic and enzymatic tests ruled out known causes of biotin dependency.
• Intracellular biotin deficiency persisted despite adequate extracellular biotin levels.

Findings:

• The patient exhibited significantly reduced biotin uptake into peripheral blood mononuclear cells (PBMCs).
• Parental PBMCs showed reduced biotin uptake, consistent with heterozygosity for an autosomal recessive disorder.
• A novel genetic defect in biotin transport was identified as the cause of biotin dependency.

Implications:

• This discovery expands the known spectrum of genetic causes for biotin dependency.
• It highlights the critical role of specific biotin transporters in cellular metabolism.
• This finding necessitates the inclusion of impaired biotin transport in the differential diagnosis of unexplained metabolic disorders.