Movement Disorder Following Hypoglycemic Encephalopathy in Mitochondrial 3-Hydroxy-3-methylglutaryl-CoA Synthase-2 (mHS) Deficiency

Mitochondrial 3-hydroxy-3-methylglutaryl-coenzyme A synthase (mHS) deficiency is an ultra-rare inborn error of ketone body synthesis that is caused by biallelic mutations in <i>HMGCS2</i>. The manifestations of mHS deficiency can include hypoketotic hypoglycemia, metabolic acidosis, lethargy, encephalopathy, hyperammonemia, and hepatomegaly. Here, we report a case of movement disorder following hypoglycemic encephalopathy involving the basal ganglia in a patient with mHS deficiency. Exome sequencing showed novel compound heterozygous variants in <i>HMGCS2</i>, a partial gene deletion (classified as pathogenic) and c.704T>A (p.M235K) variant that was deemed to be likely pathogenic. Our findings suggest that mHS deficiency can result in basal ganglia injury and movement disorder.