EN1 and sudden infant death syndrome: Given that abnormal development of pontine nuclei and mutations in En1 have been observed in several sudden infant death syndrome (SIDS) cases (Lavezzi, 2015, 2016, 2004; Weese-Mayer et al., 2004), we hypothesize that hypoxia-mediated respiratory suppression concomitant with immature responses to hypercapnia might be a major risk factor for SIDS.