Nongenetic risk factors for holoprosencephaly: An updated review of the epidemiologic literature.

Holoprosencephaly (HPE) is a major structural birth defect of the brain that occurs in approximately 1 in 10,000 live births. Although some genetic causes of HPE are known, a substantial proportion of cases have an unknown etiology. Due to the low birth prevalence and rarity of exposure to many potential risk factors for HPE, few epidemiologic studies have had sufficient sample size to examine risk factors. A 2010 review of the literature identified several risk factors that had been consistently identified as occurring more frequently among cases of HPE, including maternal diabetes, twinning, and a predominance of females, while also identifying a number of potential risk factors that had been less widely studied. In this article, we summarize a systematic literature review conducted to update the evidence for nongenetic risk factors for HPE.