Identifying the pathological mechanism of polyalanine expansion mutations in the X-linked Hypopituitarism gene SOX3

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Mental retardation (MR) is a debilitating disorder which affects 1-3% of the population. In many cases, MR results from changes (mutations) in genes which regulate the development of the brain before birth. We are studying families with an inherited form of MR termed X-linked Hypopituitarism (XH) in which only boys are affected. In addition to intellectual disability, boys with XH also have poor pituitary function resulting in short stature and slow metabolism. In severe cases, where the pituitary has failed to form completely, these babies are extremely ill and in some instances do not survive. We have previously shown that XH is due to an unusual change in the SOX3 gene in which the number of consecutive alanine residues is increased above a critical threshold (polyalanine expansion mutations). Similar mutations have recently been identified in several other genes that also cause severe birth defects. However, little is currently known about how polyalanine expansion mutations cause these disorders. The overall aim of this proposal is generate a mouse model for this disorder. Analysis of these mice will help us to answer many unresolved questions about this disorder including: How does the mutant protein cause this disorder? Which parts of the brain and pituitary are affected and how is their function altered? How does the mutant protein affect other genes and proteins in the cell? Ultimately, we hope that this mouse model will help us to develop new and improved therapies for XH and other disorders that are caused by alanine expansion mutations.