HPRT1 and hyperinsulinemic hypoglycemia, familial, 4: The disease is characterized by two major sets of defects; i.e., systemic purine metabolism expressed as hyperuricemia, gouty arthritis and renal calculi [1], and dysfunction of basal ganglia and other neural pathways associated with the hallmark biochemical defect in HPRT deficiency; i.e., markedly reduced neurotransmitter dopamine (DA) in the basal ganglia in both the human and mouse HPRT-deficient brain and resulting dystonia [2].