PCSK9 and Smith-Lemli-Opitz syndrome: Fetal cholesterol metabolism is vital in placentation and early embryogenesis,25 and PCSK9 plays a key role in its regulation.7 In syndromes characterized by extremely low LDL levels, such as SLOS, a panoply of malformations occur.8 Additionally, previous studies have described an association of lower PCSK9 levels with neural tube defects.26 There are many potential mechanisms underlying these associations supported by the results of our study.