Clinical characteristics: Biotin-thiamine-responsive basal ganglia disease (BTBGD) may present in childhood, early infancy, or adulthood. Prompt administration of biotin and thiamine early in the disease course results in partial or complete improvement within days in the childhood and adult presentations, but most with the infantile presentation have had poor outcome even after supplementation with biotin and thiamine.
Diagnosis / testing: The diagnosis of BTBGD is established in a proband with biallelic pathogenic variants in SLC19A3 by molecular genetic testing.
Management: Treatment of manifestations: Biotin (5-10 mg/kg/day) and thiamine (up to 40 mg/kg/day with a maximum of 1500 mg daily) are given orally as early in the disease course as possible and are continued lifelong. Symptoms typically resolve within days. Acute encephalopathic episodes may require care in an ICU to manage seizures and increased intracranial pressure; during acute decompensations thiamine may be increased to double the regular dose and be given intravenously. Antiepileptic drugs are used to control seizures. Treatment of dystonia is symptomatic and includes administration of trihexyphenidyl or L-dopa. Rehabilitation, physiotherapy, occupational therapy, and speech therapy as needed and adaptation of educational programs to meet individual needs. Education of the family regarding the importance of lifelong compliance with medical therapy. Prevention of primary manifestations: Prompt administration of biotin and thiamine early in the disease course. Surveillance: Clinical review of neurologic status every six months; annual assessment of developmental progress and educational needs; social support and care coordination each visit. Agents/circumstances to avoid: Infections, stress, profuse exercise and trauma. Evaluation of relatives at risk: It is appropriate to clarify the genetic status of apparently asymptomatic older and younger at-risk relatives (e.g., sibs ) of an affected individual in order to identify as early as possible those who would benefit from prompt initiation of treatment with biotin and thiamine and preventive measures (avoidance of stress and trauma). Pregnancy management: Affected women should continue thiamine and biotin during pregnancy.
Genetic counseling: BTBGD is inherited in an autosomal recessive manner. At conception, each sib of an affected individual has a 25% chance of being affected, a 50% chance of being an asymptomatic carrier, and a 25% chance of being unaffected and not a carrier. Carrier testing for at-risk family members and prenatal testing and preimplantation genetic testing for pregnancies at increased risk are possible if the SLC19A3 pathogenic variants in the family have been identified.
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