GALK1 and attention deficit-hyperactivity disorder: GALE (↑2.9X twins), UDP-galactose-4-epimerase, is one of 3–4 key enzymes in the synthesis and utilization of galactose, and changes in the other members of this family, especially GALT and GALK, were noticeably affected in the ADHD cases, with all 3 of these enzymes in the galactose processing pathway being elevated in the ADHD-affected twins (Fig. 6).