Genetic defects in PYCR2, a PYCR1 paralog, are associated with leukodystrophy-hypomyelinating 10 (HLD10; Table 2), a syndrome characterized by microcephaly and psychomotor disability (Nakayama et al., 2015; Zaki et al., 2016). Here, PYCR2 is linked to hypomyelinating leukodystrophy 10.