EDNRA and sudden infant death syndrome: We found that four SNPs at cardiorespiratory genes (ADRB2, ADRA1B, HTR1A, and EDNRA) showed evidence of association in the subgroup “prone sleeping position.” This supports the assumption that prone sleeping promotes heart and breathing problems in SIDS and that abnormalities in the noradrenergic and/or the serotonergic system, potentially in combination with the Endothelin receptor type A increase the deleterious effect of a prone position.