TPI1 and hyperinsulinemic hypoglycemia, familial, 4: Of the ∼13 pathological TPI1 mutations identified in humans so far, the Glu104Asp substitution has been the most commonly identified variant, believed to be responsible for up to 80% of all reported cases of TPI deficiency (Arya et al., 1997; Schneider and Cohen-Solal, 1996).