Because 129S6.Cdon−/− mice are capable of identifying both genetic (e.g., Boc) and non-genetic (e.g. ethanol) risk factors for HPE that are insufficient to produce HPE alone (i.e., silent cofactors) ([25], [27]; this study), we propose that they serve as a potential animal model for the assessment and identification of plausible risk factors for HPE. Here, BOC is linked to holoprosencephaly.