Mitochondrial 3-hydroxymethylglutaryl-CoA synthase-2 (HMGCS2) deficiency: a rare case with bicytopenia and coagulopathy

Mitochondrial 3-hydroxymethylglutaryl-CoA synthase-2 (HMGCS2) is the main enzyme involved in ketogenesis. It is an essential enzyme for the catalysis of β-oxidation-derived-acetyl-CoA and acetoacetyl Co-A to produce β-hydroxy-β-methylglutaryl-CoA (HMG-CoA) and free coenzyme A. The deficiency of this enzyme (3-hydoxy-3-methylglutaryl-CoA synthase) is a very rare metabolic disorder with limited cases described in the literature. The manifestations of this disease include hypoketotic hypoglycaemia, metabolic acidosis, lethargy, hepatomegaly with fatty liver and encephalopathy. We report a middle childhood male who presented with hepatosplenomegaly, lymphadenopathy and bicytopenia. The case was diagnosed by the whole exome sequencing which revealed a homozygous missense variant of uncertain significance in HMGCS2 gene.