Symptoms of GTPCH1 deficiency include hypertonia, DRD, gait difficulties, and hyperreflexia [109]. There are both autosomal dominant (AD) and autosomal recessive forms of GTPCH1 deficiency, the former being the most common cause of DRD. The gene discussed is GCH1; the disease is hyperinsulinemic hypoglycemia, familial, 4.