EDNRA and obstructive sleep apnea syndrome: For example, of 155 SNPs for the three EDN-1,-2 and-3 genes and their associated EDN receptors (EDNRA and EDNRB), there were 4 SNPs in EDN1, and 1 SNP in both of EDN2 and EDN3, in which allelic frequencies were significantly altered in children with OSA.