Expression of FGF23 in liver tissue from case 2 obtained at the time of Kasai portoenterostomy. Hepatocytes are immunoreactive for FGF23 throughout the lobule (A). Omitting of the aFGF23 in a control experiment produces negative results (A; insert). Higher magnification reveals granular pattern of cytoplasmic staining in hepatocytes (D; arrows) and faint staining in the bile duct epithelium (D; arrowhead). Liver tissue from the background liver of an infant undergoing resection of benign liver lesion serving as control is negative for significant staining in lower (B) and higher magnification (E). Biopsy material from osteoma of patient with MAS serves as biological positive control (C). At higher magnification (F), arrows denote FGF23 positive osteoblasts.