MPO and retinopathy of prematurity: Other studies have examined early postnatal protein levels in relation to ROP and, eg, reported higher levels of fibroblast growth factor 19 (FGF-19), myeloperoxidase (MPO), interleukin 8 (IL-8), interleukin 6 (IL-6), ERBB2 (formerly human epidermal growth factor receptor 2 [HER2]), and galanin (GAL), in infants who later developed ROP.