The clinical significance of these findings is illustrated in two rare syndromes: fetal akinesia deformation sequence associated with loss-of-function mutation in Nmnat2 (Lukacs et al., 2019) and two cases of childhood-onset polyneuropathy with erythromelalgia associated with a homozygous Nmnat2 mutation resulting in reduced NMNAT2 activity (Huppke et al., 2019). The gene discussed is NMNAT2; the disease is polyneuropathy.