Its release is reduced by cyclic guanosine monophosphate, nitric oxide, and ANP.10 The endothelin system is activated in models of ischaemic retinopathy and mediates pathological vascular growth.11 However, the involvement of ET1 in the pathogenesis of ROP in preterm infants and its predictive ability towards ROP remains largely unknown. The gene discussed is EDN1; the disease is retinopathy of prematurity.