FOS and sleep apnea syndrome: While these measures of hypoxemia may be influenced by conditions other than SDB, two of these genes, CD1D and RAB20, showed evidence of change with OSA treatment in the expected directions; both were expressed at lower levels in individuals with more severe SDB in FOS and MESA, and their expression increased significantly in HeartBEAT patients following treatment with CPAP, suggesting that OSA was the cause of their differential expression.