Supplementary Material for: 3-Hydroxyisobutyryl-CoA Hydrolase Deficiency in a Turkish Child with a Novel HIBCH Gene Mutation and Literature Review

3-hydroxyisobutyryl-CoA hydrolase (HIBCH) deficiency (OMIM 250620) is an autosomal recessive inborn error of valine catabolism characterized by severely delayed psychomotor development, progressive neurodegeneration, recurrent metabolic attacks with intercurrent illness, increased lactic acid, cerebral atrophy, and brain lesions in the basal ganglia. HIBCH gene defect is a very rare organic aciduria and also might cause secondary mitochondrial dysfunction. We report a 12-month-old severely affected female infant with a novel homozygous c.556C>G; p.R186G variant in the HIBCH gene presenting with axial hypotonia, severe developmental delay, and brain lesions in the basal ganglia and provide an overview of the literature. When suspected, newborn and selective screening with tandem mass analyses should include hydroxy-C4-carnitine to diagnose this disorder. However, in some cases, mostly in those with milder phenotype, diagnosis may be missed due to normal hydroxy-C4 carnitine levels.