The incidence of twinning is elevated in imprinting disorders, particularly BWS; the majority are DMZ twins with methylation loss, and MLID is also over-represented in these patients.24 25 We previously described a proband with MLID who was a DMZ twin, whose mother had a variant in NLRP5. 7 The addition of this present case supports the hypothesis that MZ twinning is connected with epigenetic disturbance in early development and, in some cases, a genetic predisposition. Here, NLRP5 is linked to Beckwith-Wiedemann syndrome.