OPRM1 and autism: In a monogenic model of autism (Oddi et al., 2013), mice lacking the Oprm1 gene that encodes the MOR (Oprm1−/−) display reduced maternal attachment in mouse pups (Moles et al., 2004), blunted social reward in juveniles (Cinque et al., 2012), impaired abilities to remember familiar social partners in a social memory test, and profound deficits in interactions with social partners (Becker et al., 2014), and heterozygous MOR knockout mice (Oprm1+/−) display similarly profound social deficits (Toddes et al., 2021).