GALK1 and hyperinsulinemic hypoglycemia, familial, 4: Based on TGAL values measured in GALK deficiency patients reported in the literature and TGAL values in the Dutch Newborn Screening cohort we suggest performing GALK screening with TGAL as a primary marker with a COV of 2500 μmol/L blood, combined with GALT enzyme activity measurement as used in the classical galactosemia screening.