Pyrroline-5-carboxylate reductase 2 (PYCR2) catalyzes the reaction of (S)-1-pyrroline-5-carboxylate with NADH + H+ to form proline and NAD+ (De Ingeniis et al. 2012). The active enzyme is inferred to be a homodecamer by virtue of its similarity to PYCR1 (Meng et al. 2006). Subcellular fractionation (De Ingeniis et al. 2012) and co-localization studies (Nakayama et al. 2015) indicate that PYCR1 is mitochondrial. Its deficiency is associated with microcephaly and hypomyelination (Nakayama et al. 2015).