VPS33B mutation with ichthyosis, cholestasis, and renal dysfunction but without arthrogryposis: Incomplete ARC syndrome phenotype

VPS33B MUTATION WITH ICHTHYOSIS, CHOLESTASIS, AND RENAL DYSFUNCTION BUT WITHOUT ARTHROGRYPOSIS: INCOMPLETE ARC SYNDROME PHENOTYPE LAURA N. BULL, PHD, VENUS MAHMOODI, BS, ALASTAIR J. BAKER, MB, CHB, ROSAMOND JONES, MS, BS, MD, SANDRA S. STRAUTNIEKS, BSC, PHD, RICHARD J. THOMPSON, BA, BM, BCH, AND A. S. KNISELY, MD

Arthrogryposis-renal dysfunction-cholestasis (ARC) syndrome is a rare multisystem disorder first described in 19791 and recently ascribed to mutation in VPS33B, whose product acts in intracellular trafficking.2 Arthrogryposis, spillage of various substances in the urine, and conjugated hyperbilirubinemia define an ARC core phenotype, in some patients associated with ichthyosis, central nervous system malformation, deafness, and platelet abnormalities.2 We describe a patient with cholestasis, aminoaciduria, ichthyosis, partial callosal agenesis, and sensorineural deafness who, although homozygous for the novel VPS33B mutation 971delA/K324fs, predicted to abolish VPS33B function, did not exhibit arthrogryposis. The phenotypes associated with VPS33B mutation may include incomplete ARC. (J Pediatr 2006;148:269-71)

CASE REPORT he first child of healthy first-cousin British parents of Pakistani origin was born at 41 weeks (birth weight, 3.37 kg). She appeared well and was discharged home. At 6 days of life (weight, 3.01 kg), she was evaluated for jaundice (serum total bilirubin [TBIL], 248 ␮mol/L; conjugated/direct bilirubin [DBIL], 94 ␮mol/L; alkaline phosphatase activity [ALP], 614 IU/L; alanine aminotransferase activity [ALT], 15 IU/L). Hypothyroidism was diagnosed (thyroid-stimulating hormone [TSH], 12.6 mU/L; free thyroxine [T4], 17.9 pmol/L); serum cortisol was adequate (518 nmol/L). At 14 days (weight 2.93 kg), jaundice had worsened (TBIL, 396 ␮mol/L; DBIL, 215 ␮mol/L; ALP, 1708 IU/L; ALT, 45 IU/L) and evidence of hypothyroidism persisted (TSH, 23.9 mU/L; T4, 20.6 pmol/L). Generalized aminoaciduria accompanied slight nonspecific elevations of some amino acid concentrations in plasma. Breast-feeding was discontinued, fat-soluble vitamins and thyroxine, 12.5 ␮g daily, were begun, and the family was referred to King’s College Hospital. On evaluation there, the infant (age 30 days, weight, 2.92 kg) had ichthyosis, jaundice, “rocker-bottom” feet without valgus or varus deformity, bilateral single palmar creases, angled palpebral fissures, and a large anterior fontanel. The liver was palpated 2 cm below the costal margin. No spleen could be felt. Gallbladder contours were abnormal From the University of California San Franon sonography, without bile duct abnormality or hepatic parenchymal inhomogeneity; cisco Liver Center Laboratory and Department of Medicine, San Francisco General stools were pigmented. Conjugated hyperbilirubinaemia had persisted, with evidence of Hospital, San Francisco, California; The Vaslightly greater hepatocellular injury (TBIL, 200 ␮mol/L [normal, 3 to 20 ␮mol/L], riety Club Children’s Hospital and Institute of Liver Studies, King’s College Hospital, DBIL 159 ␮mol/L [normal, ⬍ 4 ␮mol/L]; ALP, 1105 IU/L [normal, 30 to 130 IU/L]; London, UK; Department of Paediatrics, ALT, 74 IU/L [normal, 10 to 50 IU/L]). Serum ␥-glutamyl transpeptidase activity Wexham Park Hospital, Slough, UK; and (GGT) was not elevated (39 IU/L [normal, 1 to 55 IU/L]). Hypocoagulability and Department of Liver Studies and Transplantation, Division of Gene and Cell Based acidosis were not observed. TSH was elevated at 8.02 mU/L (normal, 0.30 to 5.50 Therapy, King’s College, London, UK. mU/L), whereas T4 was normal (16.2 pmol/L [normal, 9.0 to 25.0 pmol/L]). Cortisol was Supported in part by National Institutes of 649 nmol/L (normal, 130 to 580 nmol/L). No thyroid uptake was detected on radionuHealth grant R01 DK58214, Guy’s and St Thomas’ Charity (London, UK), and Chilclide screening. Magnetic resonance imaging found no posterior body or splenium of the dren’s Liver Disease Foundation (Birmingcorpus callosum; the pituitary gland appeared unremarkable. Ophthalmologic examinaham, UK). tion identified no lesions. A peripheral lymphocyte karyotype was 46,XX, without Submitted for publication July 21, 2005; last revision received August 16, 2005; acabnormality on in situ hybridization studies (Alagille syndrome [20p12], X-linked ichcepted October 3, 2005. thyosis [Xp22.3]). Maternal immunization against infant red-cell antigens was not deReprint requests: A. S. Knisely, MD, Institute

T

ALP ALT ARC CEA DBIL

Alkaline phosphatase activity Alanine aminotransferase activity Arthrogryposis-renal dysfunction-cholestasis Carcinoembryonic antigen Direct bilirubin

GGT LM T4 TBIL TSH

␥-glutamyl transpeptidase activity Light microscopy Thyroxine Total bilirubin Thyroid-stimulating hormone

of Liver Studies, King’s College Hospital, Denmark Hill, London SE5 9RS, UK. E-mail: [email protected]. 0022-3476/$ - see front matter Copyright © 2006 Elsevier Inc. All rights reserved. 10.1016/j.jpeds.2005.10.005

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Figure. Light micrographs of liver. A, Disarray, edema, and multinucleation of hepatocytes are seen in the patient. Carcinoembryonic antigen (CEA) lies in a finely granular, perihepatocytic distribution as well as along canaliculi (large image). In liver from an age-matched infant with documented bile salt export pump deficiency (BSEP-deficiency liver), most CEA expression by far is canalicular (inset). (Rabbit polyclonal anti-human CEA [Dako Ltd., Ely, UK] with hematoxylin counterstain; original magnification ⫻ 200.) B, Alanyl aminopeptidase (CD13) expression along canaliculi is wholly absent in patient liver, although apices of cholangiocytes (arrows) mark (large image). Compare CD13 expression in BSEP-deficiency liver, where canalicular marking as well as cholangiocyte marking are preserved (inset). (Mouse monoclonal anti-human CD13 NCL-CD13-304 [Novocastra, Newcastle-uponTyne, UK] with hematoxylin counterstain; original magnification ⫻ 400.) A115/ChemMate EnVision immunohistochemical system (Dako Ltd.) used.

monstrable. Autoantibodies and serologic evidence of TORCH agent or hepatotropic virus infection were not detected. Glucose 6-phosphate dehydrogenase and pyruvate kinase activities were normal. No mutation in CFTR was found on panel screening (33 candidates). Abnormal bile acids were not found in a urine sample. Audiologic evaluation disclosed features of sensorineural deafness. Glycosuria and failure to concentrate urine were not observed; serum concentrations of urea and creatinine were normal, as were sonograms of the kidneys. Light microscopy (LM) of a skin biopsy specimen revealed compact orthokeratosis without acantholysis or lichenoid reaction, consistent with ichthyosis. Neutral lipid was not seen in frozen sections stained with oil red O. Cytoplasmic vacuoles or osmiophilic material were not found, and platelets appeared unremarkable, on LM of glutaraldehyde-fixed buffy coat preparations exposed to osmium tetroxide. LM of a liver biopsy specimen revealed scant portal tract fibrosis with no evidence of biliary tract obstruction. Bile pigment was restricted to the lobule, in hepatocytes, bile canaliculi, and Kupffer cells. Moderate anisocytosis of hepatocytes included edema and focal multinucleation without steatosis. Several canalicular antigens were abnormally expressed (Figure). Supportive care included topical emollients, thyroxine and fat-soluble vitamin supplements, and ursodeoxycholic acid. Hearing aids were fitted. Feeding was assisted through a nasogastric tube, but growth failure persisted (at 5 months: weight, 3.68 kg [below the 0.4th percentile]; head circumference, 36.2 cm; length, 53.3 cm) and development lagged. Hyperbilirubinemia (TBIL, 172 ␮mol/L) and elevated transaminase activity (ALT, 217 IU/L) did not resolve. GGT 270

Bull et al

(56 IU/L) and creatinine and urea values remained within normal ranges. The patient died at age 6 months with pneumonia. Necropsy was not performed. The combination of ichthyosis, normal GGT despite conjugated hyperbilirubinemia (low-GGT cholestasis), aminoaciduria, and slight “neonatal hepatitis” with disordered canalicular membrane antigen expression prompted mutational analysis of VPS33B. Polymerase chain reaction of exons and exon–intron boundaries, followed by direct sequencing, identified patient homozygosity and parental heterozygosity for a single nucleotide deletion (971delA) in VPS33B; the consequent shift in reading frame, K324fs, is predicted to result in 10 altered amino acid codons followed by a stop codon. This mutation, previously undescribed, was not found on any of the 182 control chromosomes evaluated.

DISCUSSION Our patient was homozygous for a mutation in VPS33B predicted to ablate VPS33B function. Children clinically diagnosed with ARC, having the full phenotype of arthrogryposis, renal dysfunction, and cholestasis, constitute the population in which ARC was traced to mutation in VPS33B.2 Despite the mutation in VPS33B, arthrogryposis was not found. The presence of “rocker-bottom” feet was assessed as nonspecific dysmorphism, together with bilateral palmar creases and angled palpebral fissures. Generalized aminoaciduria suggested proximal tubular dysfunction, but metabolic acidosis, glycosuria, and hyposthenuria were not present, although these are considered characteristic in ARC.2 Given ichthyosis, deafness, and partial agenesis of the corpus callosum, with hypothyroidism, considerations included The Journal of Pediatrics • February 2006

Dorfman-Chanarin syndrome,3 autosomal recessive keratitisichthyosis-deafness syndrome (ichthyosiform erythroderma with corneal involvement and deafness),4 NISCH syndrome,5 and Pendred syndrome.6 In none of these, however, is lowGGT cholestasis a feature. VPS33B is implicated, by analogy with its yeast orthologue, in intracellular trafficking.2 Expression of canalicular ectoenzymes, like that of renal tubular ectoenzymes, is deficient in full-phenotype ARC patients with demonstrated VPS33B mutation.2 Recognition of this feature of full-phenotype ARC in our patient, together with aminoaciduria, low-GGT cholestasis, and ichthyosis, prompted analysis of VPS33B. To discern whether a single syndrome underlies a particular malformation or dysfunction (such as hypothyroidism in our patient) or whether multiple diagnoses must be assigned may be impossible. Mutational analysis of genes associated with particular syndromes will likely supersede solely phenotypic diagnosis. Our patient demonstrates that VPS33B-associated disease, defined by mutational analysis of VPS33B, may clinically fall short of classical ARC; indeed, other ARC patients without arthrogryposis (albeit without documented VPS33B mutation) have been reported.7 Descriptions of ARC have included central nervous system malformation,7 deafness,7 ichthyosis,8,9 and platelet dysfunction.9 These have been considered part of “an expanding range of [ARC] phenotypes.”9 We recommend that caregivers consider VPS33B disease in patients with low-GGT conjugated hyperbilirubinemia associated with any of these abnormalities. Mutational analysis of VPS33B may identify such patients as having an incomplete ARC phenotype. We further suggest assess-

VPS33B Mutation With Ichthyosis Cholestasis And Renal Dysfunction But Without Arthrogryposis Incomplete Arc Syndrome Phenotype

ment of canalicular antigen expression on liver biopsy in patients with low-GGT hyperbilirubinemia. Abnormal canalicular antigen expression may warrant mutational analysis of VPS33B.

REFERENCES 1. Nezelof C, Dupart MC, Jaubert F, Eliachar E. A lethal familial syndrome associating arthrogryposis multiplex congenita, renal dysfunction, and a cholestatic and pigmentary liver disease. J Pediatr 1979;94:258-260. 2. Gissen P, Johnson CA, Morgan NV, Stapelbroek JM, Forshew T, Cooper WN, et al. Mutations in VPS33B, encoding a regulator of SNAREdependent membrane fusion, cause arthrogryposis-renal dysfunction-cholestasis (ARC) syndrome. Nat Genet 2004;36:400-404. 3. Srinivasan R, Hadžic´ N, Fischer J, Knisely AS. Steatohepatitis and unsuspected micronodular cirrhosis in Dorfman-Chanarin syndrome with documented ABHD5 mutation. J Pediatr 2004;144:662-665. 4. Wilson GN, Squires RH Jr, Weinberg AG. Keratitis, hepatitis, ichthyosis, and deafness: report and review of KID syndrome. Am J Med Genet 1991;40:255-9. 5. Hadi-Rabia S, Baala L, Vabres P, Hamel-Teillac D, Jacquemin E, Fabre M, et al. Claudin-1 gene mutations in neonatal sclerosing cholangitis associated with ichthyosis: a tight junction disease. Gastroenterology 2004;127: 1386-1390. 6. Taylor JP, Metcalfe RA, Watson PF, Weetman AP, Trembath RC. Mutations of the PDS gene, encoding pendrin, are associated with protein mislocalization and loss of iodide efflux: implications for thyroid dysfunction in Pendred syndrome. J Clin Endocrinol Metab 2002;87:1778-1784. 7. Coleman RA, van Hove JLK, Morris CR, Rhoads JM, Summar ML. Cerebral defects and nephrogenic diabetes insipidus with the ARC syndrome: additional findings or a new syndrome (ARCC-NDI)? Am J Med Genet 1997;72:335-338. 8. Franceschini P, Barberis L. Arthrogryposis, renal tubular dysfunction, cholestasis, ichthyosis syndrome (ARCI). Eur J Pediatr 1997;156:78. 9. Eastham KM, McKiernan PJ, Milford DV, Ramani P, Wyllie J, van’t Hoff W, et al. ARC syndrome: an expanding range of phenotypes. Arch Dis Child 2001;85:415-420.

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