Revealing BCKDK Deficiency Under Autism: A Case Report, Therapeutic Outcomes, and Literature Review.

Autism spectrum disorders (ASD) are neurodevelopmental disorders characterised by defi-cits in social communication and stereotyped, restrictive behaviour. Branched-chain ketoacid dehydrogenase kinase (BCKDK) deficiency is a rare, autosomal recessive neurogenetic dis-order associated with a range of neurodevelopmental disorders, particularly ASD. We report the case of a 4.5-year-old boy with failure to thrive, microcephaly and global developmental delay. Plasma amino acid analysis revealed significantly reduced branched-chain amino acid (BCAA) concentrations. Whole-exome sequencing identified a homozygous nonsense variant in BCKDK. A multidisciplinary programme was initiated that included individualised high-protein medical nutrition therapy and oral BCAA supplementation titrated according to serial plasma levels. After eight months, plasma BCAA levels approached the lower limit of the normal range and behavioural improvements were sustained. Targeted dietary optimisation with additional BCAA supplementation partially normalised amino acid profiles and led to a measurable improvement in neurobehaviour in BCKDK deficiency, even when treatment was initiated after the diagnosis of ASD. Early metabolic screening of children with unexplained developmental delay or ASD is advisable, as timely nutrition-based intervention can improve both biochemical and neurodevelopmental outcomes.