Genetic Markers Among the Israeli Druze Minority Population With End-Stage Kidney Disease

RATIONALE & OBJECTIVE

Genetic etiologies have been identified among approximately 10% of adults with chronic kidney disease (CKD). However, data are lacking regarding the prevalence of monogenic etiologies especially among members of minority groups. This study characterized the genetic markers among members of an Israeli minority group with end-stage kidney disease (ESKD).

STUDY DESIGN

A national-multicenter cross-sectional study of Israeli Druze patients (an Arabic-speaking Near-Eastern transnational population isolate) who are receiving maintenance dialysis for ESKD. All study participants underwent exome sequencing.

SETTING & PARTICIPANTS

We recruited 94 adults with ESKD, comprising 97% of the total 97 Druze individuals throughout Israel being treated with dialysis during the study period.

PREDICTORS

Demographics and clinical characteristics of kidney disease.

OUTCOME

Genetic markers.

ANALYTICAL APPROACH

Whole-exome sequencing and the relationship of markers to clinical phenotypes.

RESULTS

We identified genetic etiologies in 17 of 94 participants (18%). None had a previous molecular diagnosis. A novel, population-specific, WDR19 homozygous pathogenic variant (p.Cys293Tyr) was the most common genetic finding. Other monogenic etiologies included PKD1, PKD2, type IV collagen mutations, and monogenic forms of noncommunicable diseases. The pre-exome clinical diagnosis corresponded to the final molecular diagnosis in fewer than half of the participants.

LIMITATIONS

This study was limited to Druze individuals, so its generalizability may be limited.

CONCLUSIONS

Exome sequencing identified a genetic diagnosis in approximately 18% of Druze individuals with ESKD. These results support conducting genetic analyses in minority populations with high rates of CKD and for whom phenotypic disease specificity may be low.

PLAIN-LANGUAGE SUMMARY

Chronic kidney disease (CKD) affects many people worldwide and has multiple genetic causes. However, there is limited information on the prevalence of genetic etiologies, especially among minority populations. Our national-multicenter study focused on Israeli Druze patients. Using exome-sequencing, we identified previously undetected genetic causes in nearly 20% of patients, including a new and population-specific WDR19 homozygous pathogenic variant. This mutation has not been previously described; it is extremely rare globally but is common among the Druze, which highlights the importance of studying minority populations with high rates of CKD. Our findings provide insights into the genetic basis of end-stage kidney disease in the Israeli Druze, expand the WDR19 phenotypic spectrum, and emphasize the potential value of genetic testing in such populations.

POS0224 A NOVEL TNFRSF1A MUTATION ASSOCIATED WITH TNF-RECEPTOR ASSOCIATED PERIODIC SYNDROME AND ITS METABOLIC SIGNATURE

Background

Tumor necrosis factor receptor-associated periodic syndrome (TRAPS) is an autosomal dominant periodic fever syndrome characterized by prolonged episodes of fever, arthralgia, myalgia, abdominal pain and erythematous rash.1 We report a new mutation in the TNFRSF1A gene which is associated with TRAPS and AA-amyloidosis. Furthermore we analyzed the metabolic changes using a metabolomics approach.

Objectives

To describe a novel mutation in the TNFRSF1A gene that causes TRAPS.

Methods

Case series. For pathogenicity predictions we used the PolyPhen-2 web-software2 and PROVEAN3. Metabolomics: Mass spectrometry was performed on patient plasma and healthy controls using an UHPLC system (Vanquish, Thermo Fisher Scientific, Bremen, Germany) coupled to an HRAM mass spectrometer (Q-Exactive Plus, Thermo Fischer Scientific GmbH, Bremen, Germany).

Results

A 44-year-old man (patient 1) presented to our hospital with abdominal pain, elevated inflammation parameters, renal failure and large proteinuria. Renal biopsy revealed AA amyloidosis. Further anamnesis showed he had suffered from recurrent attacks of abdominal pain with fever and elevation of inflammation markers since he was 16 years old. He also reported that his father, aunt, sister and daughter have had similar problems. His daughter (patient 2) reported recurrent episodes of abdominal pain with fever since she was 11 years old and his 46-year-old sister (patient 3) reported similar symptoms starting at 12 years of age. Upon presentation patient 3 showed proteinuria of 2000 mg/g creatinine (albuminuria 1500 mg/g creatinine) strongly indicating early renal AA-amyloidosis. All symptomatic family members underwent genetic testing that revealed the yet uncharacterized TNFRSF1A-variant c.332A>G (p.Q111R). In silico analysis of the mutation by PolyPhen-2 software and PROVEAN classified the mutation as probably pathogenic culminating in the diagnosis of TRAPS. All patients received canakinumab for treatment and responded with normalization of the inflammatory parameters. Patient 3 showed a marked reduction of proteinuria after 6 months of treatment. Using a metabolomics approach we were able to detect 158 distinct metabolic compounds of which 32 were up- and 35 downregulated, respectively. Two patients were analyzed before and after treatment with canakinumab. The treatment with canakinumab, however, appears to have no effect on the metabolic changes caused by TRAPS. Significantly upregulated metabolic pathways included purine metabolism, glycolysis/glyconeogenesis, glutathione metabolism, pyrimidine metabolism and phenylalanine, tyrosine and tryptophan biosynthesis. Downregulated pathways included Aminoacyl-tRNA biosynthesis, arginine and proline metabolism, arginine biosynthesis among others.

Conclusion

Here we present a novel mutation in the TNFRSF1A gene that causes TRAPS and is associated with AA-amyloidosis. Canakinumab is an effective treatment in this variant and led to improvement in proteinuria in one of the patients with presumed early renal AA-amyloidosis. We observed significant changes in the metabolome in comparison to healthy controls. Treatment with canakinumab appeared to have no effect on these metabolic changes caused by TRAPS.

References

[1]Hull, K. M. et al. The TNF receptor-associated periodic syndrome (TRAPS): Emerging concepts of an autoinflammatory disorder. Medicine (Baltimore).81, 349–368 (2002).

[2]Adzhubei, I. A. et al. A method and server for predicting damaging missense mutations. Nat. Methods7, 248 (2010).

[3]Choi, Y., Craig, J. & Institute, V. A Fast Computation of Pairwise Sequence Alignment Scores Between a Protein and a Set of Single-Locus Variants of Another Protein General Terms. Proc. ACM Conf. Bioinformatics, Comput. Biol. Biomed. - BCB ’12 doi:10.1145/2382936.

Disclosure of Interests

None declared

The ideal position of the peritoneal dialysis catheter is not always ideal

PURPOSE

Peritoneal catheter dysfunction is a frequent complication of peritoneal dialysis (PD). Traditionally, dysfunction has been attributed to catheter malposition, but whether the location of the catheter tip in the small pelvis really determines proper function is unclear.

METHODS

We reviewed 900 abdominal X-ray images of PD patients from a 7-year period in two PD units that use different catheter types (straight and Swan Neck Curled).

RESULTS

In 52% of the images, the dialysis catheter tip was located in the ideal position in the small pelvis and in 48% in other sites. Peritoneal catheter function was normal at the time of imaging in 87% of those with ideal catheter tip position, and in 74% of those with other than ideal position. The tip was located in small pelvis in 35% of images performed during catheter dysfunction and in 56% of those performed during normal catheter function. There were no differences between two catheter types. The positive predictive value of abdominal X-ray images to predict catheter function was 26%, and the negative predictive value 87%. We also found a significant positive correlation between polycystic kidney disease and normal catheter function. In contrast, obese patients were more likely to have catheter malfunction. Previous abdominal surgery was not associated with catheter dysfunction.

CONCLUSION

Our data showed a higher probability of normal function of peritoneal catheters whose tips were located in the small pelvis. However, also malpositioned catheters generally functioned well, and malpositioning of the PD catheter did not in itself explain its malfunction.

Acute compartment syndrome of the upper arm: a report of 2 cases

Compartment syndromes of the upper arm are rare clinical entities but can be a serious problem, especially in unconscious patients or those presenting with altered mental status. A high index of suspicion is needed to make an accurate diagnosis. Measuring compartment pressures is helpful, but the role of pressure measurement in the diagnosis and treatment may be secondary to the clinical examination. In patients presenting without histories of trauma, who have sustained long periods of immobilization, a suspicion of a crush syndrome should also be included during the workup of a compartment syndrome. Fasciotomy and débridement of necrotic and nonviable tissue are the treatments of choice for a patient with a compartment syndrome, but initiating medical management and providing medical stability for systemic complications resulting from a crush syndrome may be necessary prior to surgical intervention to prevent organ failure and death. Overall, prognosis is improved by early diagnosis and treatment.

Imaging of pigmented villonodular synovitis

Pigmented villonodular synovitis (PVNS) is a rare, benign, idiopathic proliferative disorder of the synovium that results in villous and/or nodular formation in joints, tendon sheaths, and bursae. The disease can be localized or diffuse. Patients with this condition typically present with symptoms of mild discomfort and associated stiffness of the involved joint; however, the spectrum of presentations is broad. Diagnosis of PVNS can be clinically difficult, and plain radiographs are usually nonspecific. Magnetic resonance (MR) imaging is a highly diagnostic modality in characterizing PVNS when it contains hemosiderin deposits exhibiting low signal intensity on all MR image pulse sequences. This article discusses the presentation, pathology, differential diagnosis, diagnostic modalities as well as various treatment options of PVNS.

A hormonal signaling pathway influencing C. elegans metabolism, reproductive development, and life span

During C. elegans development, animals must choose between reproductive growth or dauer diapause in response to sensory cues. Insulin/IGF-I and TGF-beta signaling converge on the orphan nuclear receptor daf-12 to mediate this choice. Here we show that daf-9 acts downstream of these inputs but upstream of daf-12. daf-9 and daf-12 mutants have similar larval defects and modulate insulin/IGF-I and gonadal signals that regulate adult life span. daf-9 encodes a cytochrome P450 related to vertebrate steroidogenic hydroxylases, suggesting that it could metabolize a DAF-12 ligand. Sterols may be the daf-9 substrate and daf-12 ligand because cholesterol deprivation phenocopies mutant defects. Sensory neurons, hypodermis, and somatic gonadal cells expressing daf-9 identify potential endocrine tissues. Evidently, lipophilic hormones influence nematode metabolism, diapause, and life span.

daf-12 encodes a nuclear receptor that regulates the dauer diapause and developmental age in C. elegans

The daf-12 gene acts at the convergence of pathways regulating larval diapause, developmental age, and adult longevity in Caenorhabditis elegans. It encodes a nuclear receptor most closely related to two C. elegans receptors, NHR-8 and NHR-48, Drosophila DHR96, and vertebrate vitamin D and pregnane-X receptors. daf-12 has three predicted protein isoforms, two of which contain DNA- and ligand-binding domains, and one of which contains the ligand-binding domain only. Mutations cluster in DNA- and ligand-binding domains, but correspond to distinct phenotypic classes. DAF-12 is expressed widely in target tissues from embryo to adult, but is upregulated during midlarval stages. In the adult, expression persists in nervous system and somatic gonad, two tissues that regulate adult longevity. We propose that DAF-12 integrates hormonal signals in cellular targets to coordinate major life history traits.

daf-12 regulates developmental age and the dauer alternative in Caenorhabditis elegans

From egg through adult, C. elegans has six life stages including an option for dauer formation and diapause at larval stage L3 in adverse environments. Somatic cells throughout the organism make consistent choices and advance in unison, suggesting a mechanism of coordinate regulation at these stage transitions. Earlier studies showed that daf-12, which encodes a nuclear receptor (W. Yeh, 1991, Doctoral Thesis. University of Missouri-Columbia), regulates dauer formation; epistasis experiments placed daf-12 near the end of the dauer signaling pathway. Here we describe novel daf-12 alleles that reveal a general role in advancing L3 stage programs. In these mutants, somatic cells repeat L2-specific cellular programs of division and migration at the L3 stage; epistasis experiments place daf-12 between lin-14 and lin-28 within the heterochronic pathway. We propose daf-12 and other heterochronic genes provide cellular memories of chronological stage for selecting stage-appropriate developmental programs. Endocrine factors could coordinate these stage transitions and specify developmental alternatives.

The yeast Ca(2+)-ATPase homologue, PMR1, is required for normal Golgi function and localizes in a novel Golgi-like distribution

PMR1, a Ca(2+)-adenosine triphosphatase (ATPase) homologue in the yeast Saccharomyces cerevisiae localizes to a novel Golgi-like organelle. Consistent with a Golgi localization, the bulk of PMR1 comigrates with Golgi markers in subcellular fractionation experiments, and staining of PMR1 by indirect immunofluorescence reveals a punctate pattern resembling Golgi staining in yeast. However, PMR1 shows only partial colocalization with known Golgi markers, KEX2 and SEC7, in double-label immunofluorescence experiments. The effect of PMR1 on Golgi function is indicated by pleiotropic defects in various Golgi processes in pmr1 mutants, including impaired proteolytic processing of pro-alpha factor and incomplete outer chain glycosylation of invertase. Consistent with the proposed role of PMR1 as a Ca2+ pump, these defects are reversed by the addition of millimolar levels of extracellular Ca2+, suggesting that Ca2+ disposition is essential to normal Golgi function. Absence of PMR1 function partially suppresses the temperature-sensitive growth defects of several sec mutants, and overexpression of PMR1 restricts the growth of others. Some of these interactions are modulated by changes in external Ca2+ concentrations. These results imply a global role for Ca2+ in the proper function of components governing transit and processing through the secretory pathway.

The yeast secretory pathway is perturbed by mutations in PMR1, a member of a Ca2+ ATPase family

The genes for two new P-type ATPases, PMR1 and PMR2, have been identified in yeast. A comparison of the deduced sequences of the PMR proteins with other known ion pumps showed that both proteins are very similar to Ca2+ ATPases. PMR1 is identical to SSC1, a gene previously identified by its effect on secretion of some foreign proteins from yeast. Proteins secreted from pmr1 mutants lack the outer chain glycosylation that normally results from passage through the Golgi. Loss of PMR1 function suppresses the lethality of ypt1-1, a mutation that blocks the secretion pathway. These data suggest that PMR1 functions as a Ca2+ pump affecting transit through the secretory pathway.