Question

Please DO NOT COPY from any website. UNIQUE UNIQUE

Discussion :

The "Online Mendelian Inheritance in Man" website (www.omim.org) is a great source for information about human genes and genetic traits. Each entry has a unique six-digit number. Autosomal dominant traits have entries that start with a 1, autosomal recessive traits a 2, X-linked a 3, mitochondrial a 5, and specific genes have a number that starts with a 6. I would like you to research one genetic disorder and write a brief paragraph describing the disorder as well as the gene involved and the function of the gene product (if known). To make this first topic easy, I am including a list of choices with a link to the Genetics Home Reference page which describes the gene and the function of the gene product and the entry number to search for on www.omim.org. If you choose a topic from my list then you do not need to post the reference. However, if you would prefer to choose a disorder that is not on the list then you will need to list your reputable source (.org/.gov/.edu).

Here is the list: please write about number 11. Holoprosencephaly, link http://ghr.nlm.nih.gov/gene/SHH

11. Holoprosencephaly: http://ghr.nlm.nih.gov/gene/SHH; MIM 142945

Answer 1

Holoprosencephaly is a congenital disorder characterized by the absence of division of embryonic fore brain (prosencephalon) into right and left hemispheres. This results in the defective facial development and affects the structure and function of the brain. Even though the condition can range from mild to severe, most of the cases are fatal and the babies die at birth. This disorder is classified into 3 main subtypes. Alobar, semilobar,lobar. Alobar: this is the most severe form of the three, where brain completely fails to separate resulting in facial abnormalities characterized by merged eyes and lack of nose. This from is also called cyclopia. Semilobar: less severe than alobar, where the brain is somewhat divided. Lobar: in this form there is a considerable separation of the fore brain and the baby can be born normal. This dis order is found to be inherited in some cases. Not much is known about the exact cause of this malformation, but in many cases, mutations in SHH gene coding for sonic hedgehog protein is found to cause holoprosencephaly. Sonic Hedgehog is vital in the development of the embryo. It is involved in the hedgehog pathway along with desert hedgehog or DHH and Indian hedgehog or IHH. SHH is essential for the limb development, development of the eyes, brain and spinal cord. It is also required for the division of adult stem cells. It also plays a role in the development and segmentation of the fore brain, which is required for the formation of right and left cerebral hemispheres. During embryonic development the cells forming the eyes develop into a single structure called the eye field. SHH is also required for the separation of eye field into two, forming the left and the right eyes. There are more than 100 mutations reported in the gene coding for SHH which renders the protein nonfunctional resulting in holoprosencephaly.