Arthrogryposis, renal dysfunction, and cholestasis (ARC) syndrome is a severe autosomal recessive multisystem disorder. Main characteristic features of ARC include severe failure to thrive, neonatal cholestasis, renal tubular acidosis, ichtyosis, arthrogryposis, and/or platelet dysfunction. Germline mutations in VPS33B are found in approximately 75% of individuals with ARC syndrome (1,2). VPS33B is a member of the Sec1/munc18 family proteins and forms a complex with VIPAR, which is found in RAB11-positive endosomes, and may have a role in membrane protein recycling (3). Mistargeting of apical membrane proteins to basolateral membrane of hepatocytes and renal tubular cells in the liver and kidney in patients with ARC syndrome supports a role for VPS33B-VIPAR complex in maintenance of apical polarity and may explain liver and kidney injuries (3,4). VIPAR mutations are less frequently involved in ARC syndrome than VPS33B and normal serum gamma-glutamyl transferase (GGT) cholestasis has been reported so far only in children with VPS33B mutations (2,3,5). We report here a neonate with ARC syndrome caused by VIPAR mutation, who experienced normal serum GGT cholestasis.
A girl, born at 39 weeks of gestation (birth weight 3.24 kg), was the second child of healthy first-cousin Pakistani parents and had neonatal jaundice and global hypotonia. At 43 days of life, the patient had persistent jaundice and growth failure, and was referred to our unit. The child had mild ichthyosis, global hypotonia, microretrognatism, hirsutism (Fig. 1), mild form of arthrogryposis, and cholestasis with hepatomegaly. Stool color was normal. Blood tests showed hyperbilirubinemia (total bilirubin 160 μmol/L, conjugated bilirubin 142 μmol/L). Serum transaminases and GGT activities were normal (GGT 21 IU/L, N <30). Serum bile acid concentration was increased (67 μmol/L; N <5). Abdominal ultrasonography showed normal liver/biliary tract and left hydronephrosis. Renal involvement was evidenced by proteinuria 0.88 g/L (N <0.5), β2-microglobinuria 38 mg/L (usually negative), and polyuria (>10 mL · kg−1 · h−1). The following causes of neonatal cholestasis were excluded: cystic fibrosis, α1-antitrypsin deficiency, Alagille syndrome, peroxisomal disorders, congenital disorders of glycosylation, defects of primary bile acid synthesis, and mitochondrial cytopathy. Alpha-fetoprotein level was increased (1323 IU/L; N for age <1000 IU/L). Corpus callosum hypoplasia was diagnosed on brain magnetic resonance imaging. Deafness was evidenced by a negative auditory evoked response test. No platelet anomaly was found and uneventful liver biopsy was performed. Liver histology revealed mild portal fibrosis without septa. Six portal tracts of 16 contained no bile duct. Intense hepatocellular/canalicular cholestasis and many giant hepatocytes were observed (Fig. 2). Immunostaining for canalicular proteins showed an abnormal pattern with a diffuse basolateral and canalicular signal of hepatocytes, without reinforcement of canalicular signal for carcinoembryonic antigen and bile salt export pump (BSEP) and a diffuse basolateral signal with faint, irregular, and granular canalicular reinforcement for multidrug resistance protein 3 (MDR3) (Fig. 2) (3,6). Cytokeratin 19 immunostaining confirmed relative ductopenia with slight ductular proliferation (data not shown). Supportive care included fat soluble vitamin supplements and ursodeoxycholic acid. A parenteral feeding support was needed because of a failure to thrive and severe polyuria. At age 6 months, growth failure persisted (weight <0.3 percentile), development lagged, and splenomegaly and pruritus appeared. Serum liver tests worsened: total bilirubin 163 μmol/L; aspartate aminotransferase 201 IU/L; alanine aminotransferase 1046 IU/L. Prothrombin time remained normal. Serum creatinine and urea values remained normal. The patient died at age 7 months of intestinal bleeding caused by portal hypertension. The combination of ichtyosis, tubulopathy, arthrogryposis, cholestasis with normal serum GGT activity and disorders of canalicular protein expression led to the analysis of VPS33B and VIPAR genes. No mutation was found in VPS33B. Sequence analysis of VIPAR identified a homozygous T to C base substitution at nucleotide position 1021 (c.1021T>C) resulting in the substitution of the amino acid cysteine for arginine at position 341 (p.Cys341Arg) in exon 13 (3,5). This new mutation concerned a highly conserved amino acid, even in zebrafish. In silico analysis predicted a deleterious effect.
The data reported here in a patient with ARC syndrome caused by a VIPAR mutation and with normal serum GGT cholestasis show that VIPAR defect is associated with basolateral missorting of canalicular proteins involved in bile secretion. These data confirm the role of VIPAR in apical protein sorting within hepatocytes and likely explain cholestasis in ARC syndrome.
In our patient with ARC syndrome, initial presentation may be confused with progressive familial intrahepatic cholestasis type 2 (PFIC2), especially because of mild or incomplete phenotype, at presentation (5,7). Indeed, patients with ARC syndrome, as patients with PFIC2, show cholestasis with normal serum GGT activity, increased serum α-fetoprotein and bile acids levels, and pruritus. Histological features can also be confused with PFIC2, showing numerous giant hepatocytes, fibrosis, and hepatocellular cholestasis (2–4,6,7); however, canalicular BSEP immunostaining is usually negative in PFIC2, and no BSEP basolateral signal is observed and MDR3 immunostaining is normal (6). In our patient, immunostaining studies showed a clear and abnormal redistribution of BSEP and MDR3 to the basolateral membrane compared with PFIC2 and normal human liver (6). An abnormal BSEP pattern has been reported so far in only 2 patients with ARC syndrome, 1 with a VPS33B mutation and 1 with a VIPAR mutation (3). No liver MDR3 immunostaining data have been reported so far in patients with ARC syndrome. Several other organs/systems such as kidney, brain, ear, bone, or platelets are involved in ARC syndrome, whereas PFIC2 concerns only the liver. Another cholestatic syndrome of childhood with normal serum GGT activity and pruritus is PFIC1, in which different extrahepatic signs have been reported (6). In PFIC1, canalicular BSEP immunostaining is normal or faint, but never positive at the basolateral membrane of hepatocytes and liver MDR3 immunostaining is normal (6).
In conclusion, ARC syndrome is a rare and severe recessive autosomal disorder that may be caused by VPS33B or VIPAR gene mutations. This disorder leads to a missorting of apical proteins in polarized cells that leads to multiorgan failure. Cholestasis caused by ARC syndrome may have some similarities with PFIC1-PFIC2; however, distinction can be made when liver immunostaining of biliary canalicular transporters shows a basolateral staining. BSEP targeting defect to hepatocyte canaliculus and in a lesser extent of MDR3 may explain cholestasis in ARC syndrome caused by VIPAR mutation because BSEP and MDR3 are the main biliary transporters, respectively, involved in canalicular biliary secretion of bile acids and phospholipids. ARC syndrome has to be considered in such context of cholestasis. Because of multisystem involvement and poor prognosis, it represents a contraindication to liver transplantation.
We thank Dr Bruno Stieger (University of Zurich, Switzerland) for providing us with anti-BSEP antibody and Prof Marc Tardieu (Pediatric Neurology Unit, Bicêtre Hospital, France) for neurological expertise.
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