To date, the best-studied family affected with TPI deficiency is a Hungarian family in which two germ-line identical compound heterozygote brothers have inherited a missense mutation at codon 240 encoding the Phe240Leu TPI variant and a nonsense mutation at codon 145 (Glu145TER) leading to a truncated TPI protein [18], [19]. The gene discussed is TPI1; the disease is hyperinsulinemic hypoglycemia, familial, 4.