An additional 4 cases (3 males, 1 female) had a clinical picture consistent with muscle PhK deficiency and harbored a missense variant in PHKA1 which was categorized as a VUS per ACMG criteria, including c.1745T>C (p.Ile582Thr), c.849C>G (p.Ile283Met), and c.1079T>C (p.Ile360Thr). Here, PHKA1 is linked to hyperinsulinemic hypoglycemia, familial, 4.