D2HG was postulated to be an “oncometabolite” based on reports of brain tumors in patients with congenital L2HGDH (L-2-hydroxyglutarate dehydrogenase) deficiency, in whom L2HG accumulates because it cannot be metabolized to αKG (Aghili et al., 2009, Moroni et al., 2004, Patay et al., 2012, Patay et al., 2015). This evidence concerns the gene L2HGDH and hyperinsulinemic hypoglycemia, familial, 4.