Since Sonic Hedge hog seems to start neural development does it cause most spina bifidas?
Mutations in SSH are not found in syndromes associated with abnormal neural development except in a very rare condition called holoprosencephaly in which there is failure of development of the forebrain and the face. See Essential Medical Genetics 5th ed p179-180. or http://www3.ncbi.nlm.nih.gov/htbin-post/Omim/dispmim?142945 Some very important genes such as SSH or those controlling Krebs cycle are not that important clinically as mutations tend to be lethal during embryogenesis. These vital housekeeping genes tend to be conserved across very diverse species that have separated in evolutionary terms hundreds of millions of years ago. This conservation of gene sequence tells us that most mutations are lethal, ie there is huge selective pressure to maintain the gene unchanged. SHH in man has a high degree of homology with the drosophila gene hedgehog and so is it is not surprising that mutations in this gene are not a common cause of disordered development. The clinically important gene
