Neural tube defects (NTDs) are a group of common and severe congenital birth defects that occur during early embryonic development due to incomplete closure of the neural tube. The genetic architecture of human NTDs, including spina bifida and hydrocephalus, is highly heterogeneous, with multiple genes/loci and both gene-gene and gene-environment interactions involved. Hence, the variation in outcomes also most likely relates to a combination of the severity of different variants in multiple genes and genetic modifiers affecting the biochemical traits.