DK1-CDG, also known as dolichol kinase deficiency, is caused by mutations in the DK1 (also labeled as TMEM15 or DOLK) gene (MIM 610746) [2], which encodes the enzyme responsible for the final step of the de novo biosynthesis of dolichol phosphate. Here, DOLK is linked to hyperinsulinemic hypoglycemia, familial, 4.