RRM2B and mitochondrial DNA depletion syndrome: Thirty-three individuals have been extensively genotyped and harbour RRM2B gene mutations characterized by either autosomal-recessive mitochondrial DNA depletion syndrome (Shaibani et al., 2009) or recessive and dominant mutations that cause the accumulation of multiple mitochondrial DNA deletions (Tyynismaa et al., 2009; Fratter et al., 2011; Pitceathly et al., 2011; Takata et al., 2011).