Thiamine-Responsive Maple Syrup Urine Disease in an Infant: A Rare Inborn Error of Branched-Chain Amino Acid Metabolism

Abstract

Background: Maple syrup urine disease (MSUD) is a rare autosomal recessive inborn error of metabolism caused by deficient activity of the branched-chain α-ketoacid dehydrogenase (BCKD) complex.

Case Presentation: We report the case of a 3-month-old male infant, born to a non-consanguineous couple, who presented with two episodes of seizures characterized by upward rolling of the eyes, each lasting approximately three minutes. The child also exhibited tachypnea, irritability, vomiting and poor feeding for 20 days. Exome sequencing revealed a homozygous missense variant in exon 3 of the BCKDHB gene (c.832G>A; p.Gly278Ser). The clinical and genetic findings were consistent with thiamine-responsive maple syrup urine disease. Management focused on high-dose thiamine supplementation, dietary branched-chain amino acid restriction, antiepileptic therapy, and supportive care. The infant showed marked clinical improvement and was discharged in stable condition with plans for close follow-up.

Conclusion: This case underscores the importance of considering thiamine-responsive MSUD in infants presenting with early-onset neurological symptoms and feeding difficulties. Early genetic diagnosis and targeted metabolic therapy, particularly thiamine supplementation, can lead to rapid clinical stabilization and may reduce the risk of recurrent metabolic decompensation and long-term neurodevelopmental impairment.

Cite this article as: Tasmiya D, Nazneen S, Numaan Ali M. Thiamine-responsive maple syrup urine disease in an infant: a rare inborn error of branched-chain amino acid metabolism. Pediatr Acad Case Rep. 2026;5(3):92-6.