Mitochondrial
3-hydroxy-3-methylglutaryl-CoA (
HMG-CoA) synthase (mHS) deficiency is an autosomal recessive disorder of
ketone body synthesis caused by biallelic pathogenic variants in HMGCS2. Clinical symptoms are precipitated by prolonged fasting and/or intercurrent illness with onset before the first year of life. Clinically, patients may present with hypo-/ non-ketotic
hypoglycemia,
metabolic acidosis,
hyperammonemia,
lethargy,
hepatomegaly, and
encephalopathy. During periods of decompensation, elevations of
4-hydroxy-6-methyl-2-pyrone (4-HMP), several hydroxylated hexanoic and hexenoic
acid species, and medium-chain
dicarboxylic acids in the absence of significant
ketonuria may be observed in the urine organic
acid profile. Abnormalities may also be observed in plasma which includes elevated
acetylcarnitine (C2) and 3-hydroxybutyryl/3-hydroxyisobutyryl (C4-OH)
carnitine. We report a patient who presented to the ED at 13 months of age with an undetectable point-of-care
blood glucose level. Continuous infusion of
dextrose-containing intravenous (IV) fluids were required to correct the
hypoglycemia and routine chemistries were notable for an anion gap
metabolic acidosis, transaminasemia, and elevated
creatine kinase and
lactate dehydrogenase. Urine and blood
ketones were undetectable. Qualitative assessment of urine organic
acids collected ∼46 and ∼ 99 h post-admission were significant for mild elevations of 4-HMP and hydroxy-hexanoic and hydroxy-hexenoic
acid species with a notable absence of
ketones. Previously, biochemical abnormalities in urine have been shown to normalize in as few as 27 h
after treatment giving providers a narrow window with which to obtain a critical sample. Direct communication of laboratory findings to the ordering provider guided the molecular testing and assisted in results interpretation to confirm the molecular diagnosis. Our case emphasizes the importance of collecting samples for biochemical analysis even if the critical period has been missed and acute metabolic decompensation seems to be resolved, as residual abnormalities observed in our patient greatly narrowed the differential diagnosis.