Interestingly, a SOS1 frameshift mutation (c.3248–3249insC) predicting a truncated protein lacking the C-terminal region encompassing the SH3 domain-binding and MAPK phosphorylation sites, was previously documented to be responsible for a form of hereditary gingival fibromatosis (HGF1; MIM♯ 135300), a genetically heterogeneous benign gingival overgrowth condition, in a large family [Hart et al., 2002]. This evidence concerns the gene SOS1 and hereditary gingival fibromatosis.