Genome sequencing was then requested which identified a deep intronic complex variant of unknown significance within intron 1 of HGMCL. RNA sequencing studies were sent as follow-up which revealed that the level of expression of the HMGCL gene was negligible in comparison with tissue-matched controls, thus confirming the biochemical diagnosis of HMG-CoA lyase deficiency. Here, HMGCL is linked to hyperinsulinemic hypoglycemia, familial, 4.