VPS33B and VIPAR are essential for epidermal lamellar body biogenesis and function

Mutations in VPS33B and VIPAS39 cause the severe multisystem disorder Arthrogryposis, Renal dysfunction and Cholestasis (ARC) syndrome. Amongst other symptoms, patients with ARC syndrome suffer from severe ichthyosis. Roles for VPS33B and VIPAR have been reported in lysosome-related organelle biogenesis, integrin recycling, collagen homeostasis and maintenance of cell polarity. Mouse knockouts of Vps33b or Vipas39 are good models of ARC syndrome and develop an ichthyotic phenotype. We demonstrate that the skin manifestations in Vps33b and Vipar deficient mice are histologically similar to those of patients with ARC syndrome. Histological, immunofluorescent and electron microscopic analysis of Vps33b and Vipar deficient mouse skin biopsies and isolated primary cells showed that epidermal lamellar bodies, which are essential for skin barrier function, had abnormal morphology and the localisation of lamellar body cargo was disrupted. Stratum corneum formation was affected, with increased corneocyte thickness, decreased thickness of the cornified envelope and reduced deposition of lipids. These defects impact epidermal homeostasis and lead to abnormal barrier formation causing the skin phenotype in Vps33b and Vipar deficient mice and patients with ARC syndrome.

ARC Syndrome-Linked Vps33B Protein Is Required for Inflammatory Endosomal Maturation and Signal Termination

Toll-like receptors (TLRs) and other pattern-recognition receptors (PRRs) sense microbial ligands and initiate signaling to induce inflammatory responses. Although the quality of inflammatory responses is influenced by internalization of TLRs, the role of endosomal maturation in clearing receptors and terminating inflammatory responses is not well understood. Here, we report that Drosophila and mammalian Vps33B proteins play critical roles in the maturation of phagosomes and endosomes following microbial recognition. Vps33B was necessary for clearance of endosomes containing internalized PRRs, failure of which resulted in enhanced signaling and expression of inflammatory mediators. Lack of Vps33B had no effect on trafficking of endosomes containing non-microbial cargo. These findings indicate that Vps33B function is critical for determining the fate of signaling endosomes formed following PRR activation. Exaggerated inflammatory responses dictated by persistence of receptors in aberrant endosomal compartments could therefore contribute to symptoms of ARC syndrome, a disease linked to loss of Vps33B.

The Role of Platelets and ε-Aminocaproic Acid in Arthrogryposis, Renal Dysfunction, and Cholestasis (ARC) Syndrome Associated Hemorrhage

Arthrogryposis, renal dysfunction, and cholestasis (ARC) syndrome is a rare disorder associated with platelet abnormalities resembling gray platelet syndrome. Affected patients have normal platelet numbers but abnormal morphology and function. Bleeding symptomatology ranges from postprocedural to spontaneous life-threatening hemorrhage. We report a patient with ARC syndrome and compound heterozygous mutations in VPS33B (vacuolar protein sorting 33B) who presented with significant bleeding requiring numerous admissions and transfusions. She was treated with prophylactic platelet transfusions and ε-aminocaproic acid. This was well-tolerated and significantly decreased transfusion requirements and admissions for bleeding. Our experience provides support for consideration of prophylactic measures in these patients as well as the possibility of using prophylaxis in related disorders.

Identification of novel mutations in the VPS33B gene involved in arthrogryposis, renal dysfunction, and cholestasis syndrome

Arthrogryposis, renal dysfunction, and cholestasis (ARC) syndrome is an autosomal recessive disorder caused by mutations in the VPS33B and VIPAS39. Here, we report novel mutations identified in four patients with ARC syndrome. We analyzed the entire coding regions of the VPS33B and VIPAS39 genes by direct sequencing. To detect novel splice site mutations, mRNA transcripts were analyzed by reverse transcription-polymerase chain reaction (RT-PCR) and sequencing. All four patients had compound heterozygous variants in the VPS33B gene. One patient had a previously reported splice site variant with unknown significance, c.239+5G>A, and a novel nonsense mutation, c.621G>A. The other three patients had the c.403+2T>A mutation, and each of them carried one of the splice site variants, c.239+5G>A or c.499-11G>A. c.239+5G>A and c.499-11G>A created novel splice sites which resulted in abnormal transcripts. No significant VIPAS39 mutation was detected in all patients. In patients suspected with ARC syndrome, mutation analysis of the VPS33B gene should be employed as a primary diagnostic test before performing invasive testing procedures such as organ biopsies. Performing mRNA analysis can be useful in predicting the pathogenic phenotype when the mutation seems to affect a normal splicing mechanism.

Glomerular involvement in the arthrogryposis, renal dysfunction and cholestasis syndrome

BACKGROUND

Arthrogryposis, renal dysfunction and cholestasis (ARC) syndrome is a multisystem autosomal-recessive disorder caused by defects in the VPS33B and VIPAR genes, involved in localization of apical membrane proteins. Affected children usually die by 1 year of age, often secondary to infective complications. The classic renal manifestation previously described in ARC syndrome is proximal-tubular dysfunction. The aim of this study is to gain further insight into the renal manifestations of this syndrome.

METHODS

Clinical review of three cases of ARC syndrome presenting to a tertiary centre. Together with measurement of VPS33B and VIPAR protein expression in the human glomerulus.

RESULTS

The cases demonstrated severe failure to thrive and in addition to commonly described features profound proteinuria and albuminuria, together with hypoalbuminaemia, suggesting glomerular involvement of this syndrome. Western blotting of conditionally immortalized human glomerular cells and ex vivo immunofluorescent analysis of the human glomerulus revealed that VPS33B and VIPAR were highly expressed in glomerular endothelium, and podocytes, but not in the mesangium.

CONCLUSIONS

ARC syndrome affects the glomerulus as well as the proximal tubule in the kidney. Our molecular studies suggest that both cell types that constitute the glomerular filtration barrier are affected in this condition, providing an explanation for the albuminuria that we have observed in our cases.

Cholestatic jaundice in infancy: struggling with many old and new phenotypes

Background

Clinical diagnosis of neonatal cholestasis is considered to be an extremely challenging process. Here we highlight the importance not only of the prompt distinction between extrahepatic and intrahepatic cholestasis forms, but also of the precise identification of the latter ones amongst the hotchpotch of recently discovered metabolic/genetic causes.

Biliary atresia is considered a surgical emergency in a newborn infant. The rate of success in establishing the bile drainage is in fact a function of the early age when the hepato-portoenterostomy intervention is performed. Intrahepatic cholestasis is due to a broad and more and more puzzling variety of infectious, endocrine, genetic, metabolic and toxic disorders where Gamma-glutamyl transpeptidase serum levels may help for differential diagnosis. Recently established laboratory diagnostic techniques have allowed to discover new causes of neonatal cholestasis. Aim of the Commentary is to go through some of them and bring the focus particularly on the information deriving from the paper by Pinon et al. in this issue of the Journal, which paves the way to the inclusion of the hepatocyte nuclear factor-1-beta deficiency as a new condition to consider in the diagnostic process of the syndromic forms with paucity of intralobular bile ducts.

Conclusion

Neonatal cholestasis poses diagnostic challenges in practice. Recent advances in the pathophysiology and in molecular genetics together with clinical features, histopathologic findings and careful reasoning remains paramount to put together the pieces of the jigsaw.

An uncommon case of arthrogryposis, renal dysfunction, and cholestasis (ARC) syndrome and review of the renal involvement: Questions

Arthrogryposis, renal dysfunction, and cholestasis syndrome is a rare autosomal recessive disorder caused by mutations in the VPS33B and VIPAR genes. Most cases are fatal within the first year of life. Here we describe one of the two oldest patients with arthrogryposis, renal dysfunction, and cholestasis syndrome. This is a 12-year-old Hispanic female, from a non-consanguineous parents, diagnosed with an incomplete phenotype of arthrogryposis, renal dysfunction, and cholestasis syndrome with arthrogryposis and renal tubular dysfunction but without cholestasis. At 11 years of age, she was found to have impaired renal function, nephrotic-range proteinuria, Fanconi syndrome, and distal renal tubular acidosis. She also had hypercalciuria, nephrogenic diabetes insipidus, and small kidneys by renal ultrasound. Genetic analysis using whole exome sequencing showed a mutation and a partial deletion in the VPS33B gene. Further studies showed that the mother has a partial deletion in the VPS33B gene. Her medication regimen includes potassium citrate and enalapril.

The Sec1/Munc18 protein VPS33B forms a uniquely bidirectional complex with VPS16B

Loss of function variants of VPS33B and VIPAS39 (encoding VPS16B) are causative for arthrogryposis, renal dysfunction and cholestasis (ARC) syndrome, where early lethality of patients indicates that VPS33B and VPS16B play essential cellular roles. VPS33B is a member of the Sec1/Munc18 (SM) protein family, and thus thought to facilitate vesicular fusion via interaction with SNARE complexes, as does its paralog VPS33A in the homotypic fusion and vacuole sorting (HOPS) complex. VPS33B and VPS16B have been shown to associate, but little is known about the composition, structure or function of the VPS33B/VPS16B complex. We show here that human VPS33B/VPS16B is a high molecular weight complex, which we expressed in yeast to obtain material for structural, composition and stability analysis. Circular dichroism data indicate VPS33B/VPS16B has a well-folded α-helical secondary structure, for which size exclusion chromatography-multi angle light scattering revealed a MW of ∼315 kDa. Quantitative immunoblotting indicated the complex has a VPS33B:VPS16B ratio of 2:3. Expression of ARC syndrome-causing VPS33B missense variants showed that L30P disrupts complex formation, but not S243F or H344D. Truncated VPS16B containing amino acids 143-316 was sufficient to form a complex with VPS33B. Small angle X-ray scattering and negative staining electron microscopy revealed a two-lobed shape for VPS33B/VPS16B. Avidin tagging indicated that each lobe contains a VPS33B molecule, and they are oriented in opposite directions. From this we propose a structure for VPS33B/VPS16B that allows the copies of VPS33B at each end to interact with separate SNARE bundles and/or SNAREpins, plus their associated membrane components. Thus our observations reveal the only known potentially bidirectional SM protein complex.

VIPAS39 related arthrogryposis-renal dysfunction-cholestasis syndrome-case report and systematic review

BACKGROUND

Arthrogryposis-renal dysfunction-cholestasis (ARC) syndrome, a rare autosomal recessive disorder, exhibits genetic heterogeneity with the VIPAS39 gene pathological variants being a distinct contributor.

RESULTS

We present two related patients from Kosovo, describing the clinical, genetic, and therapeutic aspects of the syndrome. The identified novel VIPAS39 pathological variants (c.762G > A; c.1064_1082delinsAGTG) emphasize the complex phenotypic expression of ARC syndrome. A systematic literature review identified 8 VIPAS39-related ARC cases with notable variability in clinical features. Prognostically, patients fell into severe and milder groups, with some reaching adolescence. Our report aligns with others noting milder ARC courses and emphasizes the value of genetic testing, especially in atypical presentations. Challenges included incomplete literature data, early mortality affecting diagnostic workup, and limited VIPAS39-related ARC cases. Comparisons with the more prevalent VPS33B pathological variants revealed no distinct clinical differences.

CONCLUSION

Our study expands understanding of ARC syndrome, highlighting its genetic diversity and clinical variability. Milder presentations underscore diagnostic challenges and the potential prevalence of undiagnosed cases. Increased awareness and comprehensive genetic testing are crucial for early and accurate diagnosis.

Arthrogryposis-renal tubular dysfunction-cholestasis syndrome: a cause of neonatal cholestasis. Case report

Arthrogryposis-renal dysfunction-cholestasis syndrome is a rare lethal disorder that involves multipl organ system. It is inherited autosomal recessive and caused by defects in the VPS33B and VIPAR genes. Three cardinal findings of this syndrome are arthrogryposis, renal tubular dysfunction and cholestasis.The other organ involvements including ichthyosis, central nervous system malformation, platelet anomalies, congenital heart defects and severe failure to thrive are sometimes associated with this syndrome. Clinical findings, organ biopsy and mutational analysis can help for diagnosing but there is no curative treatment except supportive care. Several symptoms of this condition are already usually present in the neonatal period: arthrogryposis, neonatal cholestasis, skin lesions, among others. Usually survival is until the first year of life. We present a newborn whose evolution was rapidly fatal.

Two novel mutations in VPS33B gene cause a milder ARC syndrome with prolonged survival in a 12-year-old patient: Case report

Arthrogryposis-renal dysfunction-cholestasis (ARC) syndrome is a rare autosomal recessive disease caused by VPS33B and VIPAR gene mutations. The main clinical manifestations are congenital joint contracture, renal dysfunction mainly characterized by distal renal tubular dysfunction, and low glutamyltransferase cholestasis. Most patients with ARC die within 2 years of birth. Here, we report the case of a 12-year-old girl with an ARC phenotype who experienced long-term survival with only mild clinical symptoms. We detected two new heterozygous mutation sites of the VPS33B gene in this child, c.1081C > T (p.GLN361X, 257) and c.244T > C (p.Cys82Arg), through the gene detection technique; the tertiary structure of the protein was predicted by using the SWISS-model. We further reviewed the literature and summarized the clinical manifestations and gene loci of 19 ARC syndrome patients with long-term survival reported so far.