MKS3-related ciliopathy with features of autosomal recessive polycystic kidney disease, nephronophthisis, and Joubert Syndrome.

OBJECTIVES: To describe 3 children with mutations in a Meckel syndrome gene (MKS3), with features of autosomal recessive polycystic kidney disease (ARPKD), nephronophthisis, and Joubert syndrome (JS). STUDY DESIGN: Biochemical evaluations, magnetic resonance and ultrasound imaging, electroretinograms, IQ testing, and sequence analysis of the PKHD1 and MKS3 genes were performed. Functional consequences of the MKS3 mutations were evaluated by cDNA sequencing and transfection studies with constructs of meckelin, the protein product of MKS3. RESULTS: These 3 children with MKS3 mutations had features typical of ARPKD, that is, enlarged, diffusely microcystic kidneys and early-onset severe hypertension. They also exhibited early-onset chronic anemia, a feature of nephronophthisis, and speech and oculomotor apraxia, suggestive of JS. Magnetic resonance imaging of the brain, originally interpreted as normal, revealed midbrain and cerebellar abnormalities in the spectrum of the "molar tooth sign" that characterizes JS. CONCLUSIONS: These findings expand the phenotypes associated with MKS3 mutations. MKS3-related ciliopathies should be considered in patients with an ARPKD-like phenotype, especially in the presence of speech and oculomotor apraxia. In such patients, careful expert evaluation of the brain images can be beneficial because the brain malformations can be subtle.

Rapid evolution of congenital hepatic fibrosis after liver transplantation for acute liver failure: the potential role of extrahepatic factors.

A 9-year-old male underwent deceased donor liver transplantation for idiopathic fulminant hepatic failure. In the postoperative period, a review of perioperative biopsies of the donor liver revealed mild features of congenital hepatic fibrosis. Over the ensuing year, the recipient developed severe complications of congenital hepatic fibrosis including multiple episodes of cholangitis and progressive portal hypertension. After a second transplant, the patient had no further episodes of cholangitis and/or features of portal hypertension. Examination of the explanted liver revealed remarkable progression of the congenital hepatic fibrosis, suggesting that the phenotype of this disease may be dependent in part on extrahepatic factors.

Polyductin, the PKHD1 gene product, comprises isoforms expressed in plasma membrane, primary cilium, and cytoplasm.

BACKGROUND: PKHD1, the autosomal-recessive polycystic kidney disease (ARPKD) gene, encodes multiple alternatively spliced transcripts predicted to generate membrane-bound and secreted proteins. The longest open reading frame encodes polyductin (fibrocystin), a putative 4074 amino acid protein with a single transmembrane domain and an intracellular C-terminus. METHODS: To characterize the PKHD1 products and their expression profile, we raised polyclonal antibodies against different portions of polyductin and analyzed different organs using various methods. RESULTS: Western blot analyses demonstrated specific bands of >440 kD in human adult kidney, liver, and pancreas and approximately 230 kD in kidney and liver, predominantly observed in membrane fractions. The >440-kD putative membrane protein was immunoprecipitated from kidney and subsequently detected by Western blotting using two distinct antisera. An additional product of approximately 140 kD was specifically recognized by affinity-purified antisera predominantly in soluble fractions. Immunohistochemistry studies revealed specific staining in cortical and medullary collecting ducts and thick ascending limbs of Henle (TALH). Serial sections were stained with antibodies against aquaporin-2 and Tamm-Horsfall protein to confirm the nephron segment localization. Positive staining was also detected in biliary and pancreatic duct epithelia. Analyses of mouse developing tissues showed specific staining in the ureteric bud branches, intra- and extrahepatic biliary ducts, pancreatic ducts, and salivary glands. Immunofluorescence studies in inner medullary collecting duct cultured cells and immunoelectron microscopy analysis of medullary collecting ducts demonstrated that the protein localizes to the primary cilium. Positive signal was also detected in the apical membrane and in cytoplasm. CONCLUSION: The results indicate that polyductin is part of the group of polycystic kidney disease (PKD)-related proteins expressed in primary apical cilia. Our data also suggest that, in addition to its likely involvement in cilia function, polyductin probably serves in other subcellular functional roles. The detection of three different products using two antisera, with evidence for distinct subcellular localizations, suggests that PKHD1 encodes membrane-bound and soluble isoforms.