In the immense majority of cases, the defect is located on the posterior vertebral arches. Incidence It is the most common CNS malformation.
Incidence varies according to geographic location, ethnic background and year seasons.
It is more prevalent in the British Isles and less common in Eastern countries. Likewise, spina bifida is more frequent in Caucasians when compared to Orientals or Africans. These differences seem to persist even after eventual migrations, suggesting that genetic influence is more pronounced than the environmental one. The pattern of inheritance is multifactorial. It can also occur as part of Mendelian syndromes, chromosomal disorders or secondary to exposure to teratogenic agents like valproic acid, aminopterin and thalidomide.