Furthermore, the data with [1‐13C]‐galactose on carriers of GALT deficiency and patients with severe classic galactosemia due to GALT deficiency as well as patients with hypomorphic forms due to p.Ser135Leu variant are comparable to our previous reports.13, 20, 21, 22. This evidence concerns the gene GALT and hyperinsulinemic hypoglycemia, familial, 4.