XYLT2 and hereditary gingival fibromatosis: A more plausible gene in this region, which is in fact closer to our associated SNP, is SOS2. Although SOS2 has not previously been implicated in periodontal health, disruption of its closely related homolog, SOS1, is responsible for hereditary gingival fibromatosis (Hart et al. 2002), suggesting a plausible role of SOS genes (Ras-specific exchange factors) in periodontal health.