HTRA1 and retinopathy of prematurity: Furthermore, when considering a second, ethnically diverse validation cohort, we confirm the significance of elevated systemic HTRA-1 expression to the development of ROP and show that the likelihood of ROP development relative to systemic HTRA-1 expression demonstrates a dose-response, specifically a 2.32 increased rate of ROP development for each doubling of systemic HTRA-1 expression.