HOXB4 and neural tube defect: To investigate the potential clinical relevance of expression levels of the selected HOX genes in anencephaly, we first examined the mRNA level of HOX genes, including HOXA4, HOXA5, HOXB4, HOXB5, HOXC4, HOXC5, HOXD1, HOXD3, HOXD4, and HOXD8 in brain tissues from 39 NTD-affected and 39 normal control human fetuses.