SOS1

The SOS1 gene provides instructions for making a protein that is involved in pathways within cells that control growth and development. Normally, this protein regulates another protein, called Ras, that stimulates cells to grow and divide. This regulation tightly controls the growth of cells and tissues, and is especially important for proper embryonic development.

Noonan syndrome - caused by mutations in the SOS1 gene

More than 20 mutations causing Noonan syndrome have been identified in the SOS1 gene. These mutations change one protein building block (amino acid) in the SOS1 protein. These changes are believed to cause the protein to be continuously active, rather than switching on and off in response to other cellular proteins. The constant activation disrupts the regulation of systems that control cell functions such as growth and division. Researchers believe that increased SOS1 protein activation leading to defective cell movement and differentiation (the process by which cells mature to carry out specific functions) could play a role in the signs and symptoms of Noonan syndrome such as short stature and facial abnormalities.

other disorders - caused by mutations in the SOS1 gene

Mutations in the SOS1 gene can also cause hereditary gingival fibromatosis type 1. This disorder is characterized by a slowly progressive overgrowth of the tissue of the gums (gingiva). Too much of this tissue can impair teeth from pushing through the gums, which can cause difficulties in speech and chewing food. So far only one mutation in the SOS1 gene has been shown to cause hereditary gingival fibromatosis type 1. This mutation is an addition of a single building block of DNA (nucleotide) which disrupts the gene's instructions and causes a shortened protein to be made. Unlike the normal SOS1 protein, the shortened protein is permanently active. Instead of triggering cell growth in response to particular signals from outside the cell, the overactive protein directs cells to grow and divide constantly. It is unclear why the overgrowth of tissue is seen only in the gums.