Morphologic findings in progressive familial intrahepatic cholestasis 2 (PFIC2): correlation with genetic and immunohistochemical studies.

Progressive familial intrahepatic cholestasis, type 2 (PFIC2), characterized by cholestasis in infancy that may progress to cirrhosis, is caused by mutation in ABCB11, which encodes bile salt export pump (BSEP). We correlated histopathologic, immunohistochemical, and ultrastructural features in PFIC2 with specific mutations and clinical course. Twelve patients with clinical PFIC2 and ABCB11 mutations were identified, and 22 liver biopsy and explant specimens were assessed. All had hepatocellular cholestasis; most had canalicular bile plugs. At least 1 specimen from every patient had centrizonal/sinusoidal fibrosis, often with periportal fibrosis. Neonatal hepatitis-like features (inflammation, giant cells, necrosis) varied. In 2 of the 5 patients with paired specimens obtained >6 months apart, lobular and portal fibrosis worsened. Transmission electron microscopy (EM) in all 9 patients studied showed canalicular dilatation, microvilli loss, abnormal mitochondrial internal structure, and varying intracanalicular accumulation of finely granular bile. Canalicular staining for BSEP was absent in 10 patients and present in 2 patients, 1 of whom had intermittent symptoms. ABCB11 sequencing of all patients identified 6 novel and 10 previously described mutations, with nonsense, missense, and/or noncoding mutations in the 10 patients without immunohistochemically demonstrable BSEP. Missense and/or noncoding mutations were identified in the 2 patients with demonstrable BSEP, whose clinical course was more indolent. Mutations ending ABCB11 transcription appear linked, through hepatocellular necrosis and fibrosis, to worse outcome. In conclusion, light microscopy and electron microscopy findings in clinical PFIC2 can support diagnosis, but are variable and nonspecific. Therefore, no correlation between specific mutations and histopathology is yet possible.