Criticisms of �Sonic Hedgehog� Bibliography
Mutations in the shh gene range from single base pair substitutions to the deletion of a large stretches of compositional DNA, in most cases rendering a malformed and nonfunctional protein product. The mutations can be inherited from a parent or simply the product of an unfortunate transposition error during meiosis. In either situation, the resulting protein may lack the ability to bind to Ptc based on how adversely its normal conformation is changed. If shh does not bind to Ptc, then the development of the embryo will lack appropriate coordination and HPE results. The alobar form, in which the brain fails to separate any degree, usually results in a stillbirth (or potentially severe defects such as cyclopia which has occurred in the form that affects cats). A semilobar case usually results in a cleft lip and palate along with various internal anomalies.
Aside from the mutation of shh, the drinking of alcohol while pregnant can cause what is virtually HPE. Alcohol has the potential to act as an inhibitor of the shh signaling pathway. When a pregnant woman drinks alcohol, it can be transferred from her blood stream to the fetus by way of the umbilical cord. The alcohol introduced in this way then has the ability to turn off the shh pathway, and the fetus will basically have a case of HPE although the mutation of a gene is not involved. This is an utterly pitiful way for a baby to develop a deformity (Holoprosencephaly, 2008).
Further Reading: http://www.holoprosencephaly.net/Holoprosencephaly
This web page was produced as an assignment for an AP Biology course at Montgomery High School.