In the cblE and cblG defect, macrocytic anaemia (Vilaseca et al 2003; Kvittingen et al 1997) and neurocognitive performance (Harding et al 1997; Rosenblatt et al 1985; Schiff et al 2011; Kvittingen et al 1997; Müller et al 2007) often respond to treatment (Müller et al 2007; Schiff et al 2011). The gene discussed is MTR; the disease is macrocytic anemia.