Classical galactosaemia (CG) caused by galactose‐1‐phosphate uridyltransferase (GALT) deficiency occurs secondary to bi‐allelic GALT variants (OMIM#230400), at an incidence of ~1/50 000 live‐births in Caucasians.1 Here, GALT is linked to hyperinsulinemic hypoglycemia, familial, 4.