Expressed in muscle, heart, kidney and liver but barely detectable in lung, pancreas and brain. In liver veins, expressed in hepatic vein, extrahepatic portal vein and intrahepatic portal vein. Defects in C4orf54 may cause obliterative portal venopathy (OVP), a defect characterized by lesions of the intrahepatic branches of the portal vein that may lead to the occlusion or the obliteration of the small branches of the portal vein. Obliterative portal venopathy is currently thought to be responsible for many cases of portal hypertension in the absence of cirrhosis or obstruction of large portal or hepatic veins. Authors suggest a pathogenic role of FOPV mutations in some familial cases of OPV, with a pattern of autosomal dominant inheritance with incomplete penetrance and variable expressivity. Also, FOPV mutations may be involved in some non-familial cases (PubMed:28792652).