Identification of genes and signaling pathways associated with arthrogryposis‑renal dysfunction‑cholestasis syndrome using weighted correlation network analysis

A New Aberration in the VPS33B Gene Leads to Full-Symptom ARCS1

BACKGROUND ARCS1 is an acronym for arthrogryposis, renal dysfunction, and cholestasis. It is a congenital malfunction with autosomal recessive inheritance, and, unfortunately, its prognosis is still poor. It is believed that VPS33B is altered in 75% of cases and that the VIPAR gene is altered in approximately 25% of them. CASE REPORT An affected child was born from the first pregnancy of 26-year-old mother and a 30-year-old father with no previous medical history and no genetic conditions. The first clinical symptoms were observed at the end of the child's second week of life. The mother reported the child has decreasing body weight and loss of appetite. After admission to the ward, the child was apathetic and sleepy. Symptoms of conjunctivitis, pale and dry skin, and mild face and mild body dysmorphia were observed. CONCLUSIONS Laboratory tests revealed proteinuria of up to 1.36 g/l and glycosuria of up to 28 mmol/l, as well as fluctuating metabolic acidosis. The bilirubin level reached 6.62 mg/dl, along with alkaline phosphatase at 470 U/l. Moreover, hypothyroidism with TSH at 16.71 uU/ml was observed. Because of the co-occurrence of cholestasis and renal dysfunction, molecular testing was done. The 17th exon of VPS33B was sequenced by Sanger DNA sequencing method. To the best of our knowledge, this is the first report of homozygotic mutation c.1235_1236delinsG (p.Pro412ArgfsTer7) in the VPS33B gene. The risk of transfer of the mutation to future descendants was calculated as 25%. Due to the wide landscape of molecular alternation in the 17th exon of the VPS33B gene, we propose using Sanger whole-exon sequencing as a first-choice diagnostic test.

A Novel Mutation of VPS33B Gene Associated with Incomplete Arthrogryposis-Renal Dysfunction-Cholestasis Phenotype

Arthrogryposis-renal dysfunction-cholestasis (ARC) syndrome is an autosomal recessive disorder caused by mutations of the VPS33B encoding the vacuolar protein sorting 33B (VPS33B), which is involved in the intracellular protein sorting and vesicular trafficking. We report a rare case of ARC syndrome without arthrogryposis caused by a novel mutation of VPS33B. A female patient of Greek origin presented on the 14^th day of life with renal tubular acidosis, Fanconi syndrome, nephrogenic diabetes insipidus, and cholestasis with normal gamma-glutamyl transpeptidase, without arthrogryposis and dysmorphic features. She was born to apparently healthy, nonconsanguineous parents. Additional features included dry and scaling skin, generalized hypotonia, hypoplastic corpus callosum, neurodevelopmental delay, failure to thrive, short stature, recurrent febrile episodes with and without infections, and gastrointestinal bleeding. DNA testing revealed that the patient was homozygous for the novel c.1098_1099delTG (p.Glu367Alafs∗17) mutation of exon 14 of VPS33B gene (NM_018668) on chromosome 15q26.1, leading to a nonsense frameshift variant of VPS33B with premature termination of translation. Her parents were heterozygous for the same VPS33B mutation. The prognosis was predictably poor in the context of the intractable polyuria necessitating long-term parenteral fluid administration via indwelling central catheter leading to catheter-related sepsis, to which she eventually succumbed at the age of 7 months. This is the first published VPS33B mutation in an ARC patient of Greek origin. The current case adds to the spectrum of ARC-associated VPS33B mutations and provides evidence supporting the existence of incomplete ARC phenotype. Increased awareness and early genetic testing for ARC are suggested in cases with isolated cholestasis and/or renal tubular dysfunction, even in the absence of arthrogryposis.

Quantitative Trait Locus and Integrative Genomics Revealed Candidate Modifier Genes for Ectopic Mineralization in Mouse Models of Pseudoxanthoma Elasticum

Pseudoxanthoma elasticum, a prototype of heritable multisystem ectopic mineralization disorders, is caused by mutations in the ABCC6 gene encoding a putative efflux transporter, ABCC6. The phenotypic spectrum of pseudoxanthoma elasticum varies, and the correlation between genotype and phenotype has not been established. To identify genetic modifiers, we performed quantitative trait locus analysis in inbred mouse strains that carry the same hypomorphic allele in Abcc6 yet with highly variable ectopic mineralization phenotypes of pseudoxanthoma elasticum. Abcc6 was confirmed as a major determinant for ectopic mineralization in multiple tissues. Integrative analysis using functional genomics tools that included GeneWeaver, String, and Mouse Genome Informatics identified a total of nine additional candidate modifier genes that could influence the organ-specific ectopic mineralization phenotypes. Integration of the candidate genes into the existing ectopic mineralization gene network expands the current knowledge on the complexity of the network that, as a whole, governs ectopic mineralization in soft connective tissues.