OPRM1 and neonatal abstinence syndrome: Some genetic polymorphisms of genes related to dopamine and endogenous opioid systems such as prepronociceptin (PNOC) (Wachman et al., 2017), opioid receptors (Wachman et al., 2015) (OPRM1, OPRK1, and OPRD1), and catechol-O-methyltransferase (COMT) (Wachman et al., 2013), seem associated to a more severe NAS outcome, although further test on a larger scale are required to confirm these indications.