This study aimed to investigate the influence of variants in genes postulated for IH—specifically, anthrax toxin receptor 1 (ANTXR1), beta-2-adrenergic receptor (ADRB2), Fms-related tyrosine kinase 4 receptor (FLT4), kinase insert domain receptor (KDR), and insulin-like growth factor 1 receptor (IGF1R)—on the development and severity of ROP. The gene discussed is FLT4; the disease is isolated hemihyperplasia.