Novel UMOD mutations in familial juvenile hyperuricemic nephropathy lead to abnormal uromodulin intracellular trafficking

UMOD Mutations in Chronic Kidney Disease in Taiwan

UMOD is the first identified and the most commonly mutated gene that causes autosomal dominant tubulointerstitial kidney disease (ADTKD). Recent studies have shown that ADTKD-UMOD is a relatively common cause of chronic kidney disease (CKD). However, the status of ADTKD-UMOD in Taiwan remains unknown. In this study, we identified three heterozygous UMOD missense variants, c.121T > C (p.Cys41Arg), c.179G > A (p.Gly60Asp), and c.817G > T (p.Val273Phe), in a total of 221 selected CKD families (1.36%). Two of these missense variants, p.Cys41Arg and p.Gly60Asp, have not been reported previously. In vitro studies showed that both uromodulin variants have defects in cell membrane trafficking and excretion to the culture medium. The structure model predicted altered disulfide bond formation in both variants, but only p.Gly60Asp was predicted to cause protein destabilization. Our findings extend the mutation spectrum and indicate that the ADTKD-UMOD contributed to a small but significant cause of CKD in the Taiwanese population.

An intermediate-effect size variant in UMOD confers risk for chronic kidney disease

The kidney-specific gene UMOD encodes for uromodulin, the most abundant protein excreted in normal urine. Rare large-effect variants in UMOD cause autosomal dominant tubulointerstitial kidney disease (ADTKD), while common low-impact variants strongly associate with kidney function and the risk of chronic kidney disease (CKD) in the general population. It is unknown whether intermediate-effect variants in UMOD contribute to CKD. Here, candidate intermediate-effect UMOD variants were identified using large-population and ADTKD cohorts. Biological and phenotypical effects were investigated using cell models, in silico simulations, patient samples, and international databases and biobanks. Eight UMOD missense variants reported in ADTKD are present in the Genome Aggregation Database (gnomAD), with minor allele frequency (MAF) ranging from 10-5 to 10-3. Among them, the missense variant p.Thr62Pro is detected in ∼1/1,000 individuals of European ancestry, shows incomplete penetrance but a high genetic load in familial clusters of CKD, and is associated with kidney failure in the 100,000 Genomes Project (odds ratio [OR] = 3.99 [1.84 to 8.98]) and the UK Biobank (OR = 4.12 [1.32 to 12.85). Compared with canonical ADTKD mutations, the p.Thr62Pro carriers displayed reduced disease severity, with slower progression of CKD and an intermediate reduction of urinary uromodulin levels, in line with an intermediate trafficking defect in vitro and modest induction of endoplasmic reticulum (ER) stress. Identification of an intermediate-effect UMOD variant completes the spectrum of UMOD-associated kidney diseases and provides insights into the mechanisms of ADTKD and the genetic architecture of CKD.

Autosomal dominant tubulointerstitial kidney disease with a novel heterozygous missense mutation in the uromodulin gene: A case report

BACKGROUND

Autosomal dominant tubulointerstitial kidney disease (ADTKD) is a progressive chronic disease that is inherited in an autosomal dominant fashion. Symptoms include hyperuricemia, gout, interstitial nephritis, renal cysts, and progressive renal damage that can lead to end-stage renal disease. Mutations in the uromodulin gene (UMOD) characterize the ADTKD-UMOD clinical subtype of this disease. To date, > 100 UMOD mutations have been identified. Early diagnosis of ADTKD-UMOD is important to treat the disease, slow down disease progression, and facilitate the identification of potentially affected family members.

CASE SUMMARY

We report a 40-year-old man harboring a novel heterozygous missense mutation in UMOD (c.554G>T; p. Arg185Leu). The patient had hyperuricemia, gout, and chronic kidney disease. The same mutation was detected in his daughter, aunt and cousin.

CONCLUSION

A single nucleotide substitution in exon 3 of UMOD was responsible for the heterozygous missense mutation (c.554G>T, p.Arg185Leu).

Familial juvenile hyperuricemia in early childhood in a boy with a novel gene mutation

Familial juvenile hyperuricemic nephropathy (FJHN) is a rare autosomal dominant disease caused by mutations in the uromodulin (UMOD) gene. It is characterized by the development of gout, tubulointerstitial nephropathy, and end-stage renal disease. Here we report a case of FJHN that was diagnosed in early childhood in a boy with a novel gene mutation. At the age of 4 years, the patient was admitted with a diagnosis of purpura nephritis. He was discharged following symptom alleviation. However, hyperuricemia (7-9 mg/dL) and mild renal dysfunction [creatinine-estimated glomerular filtration rate (eGFR): 80-90 mL/min/1.73 m²] persisted after discharge. FJHN was suspected on the basis of a maternal family history of hyperuricemia, renal dysfunction, and dialysis. Direct sequence analysis performed at the age of 5 years revealed a novel missense mutation (c766T > G), p.Cys256Gly, in exon 3. Urate-lowering therapy was started, which provided good uric acid control (6.0 mg/dL). At the age of 8 years, persistent renal dysfunction was observed (eGFR: 80-90 mL/min/1.73 m²). Interestingly, cases of FJHN with c744C > G (p.Cys248Trp) mutations also exhibit a high incidence of juvenile onset, and identical disulfide bridges are considered responsible for the accumulation of mutant UMOD in the endoplasmic reticulum. Pediatricians should consider UMOD mutation analysis for families with autosomal dominant tubulointerstitial kidney disease (ADTKD) and a bland urinary sediment, even if hyperuricemia is mild. Also, sex and genotype are very important prognostic factors for ADTKD caused by UMOD mutations.

Autosomal dominant tubulointerstitial kidney disease genotype and phenotype correlation in a Chinese cohort

Genes of UMOD, HNF1B, MUC1, REN and SEC61A1 were reported to be associated with autosomal dominant tubulointerstitial kidney disease (ADTKD). 48 probands and their family members (N = 27) were enrolled in this genetic screening study. A combination of methods was employed for comprehensive molecular analysis of both copy number variations (CNVs) and single nucleotide variants (SNVs). 35 probands were followed for years. The phenotype-genotype and genotype-outcome correlation were inferred from these datasets. In this cohort, 18 probands were diagnosed with ADTKD, according to Kidney Disease: Improving Global Outcomes (KDIGO) guideline. Moreover, 11 probands were diagnosed with ADTKD-UMOD, one with ADTKD-REN and one with ADTKD-HNF1B, based on molecularly confirmed pathogenic variants. The 11 UMOD variants were mainly located in codons 28 to 289 and half of the variants were found to change the cysteine amino acid. According to the follow-up data, suspected ADTKD individuals had a better prognosis compared to ADTKD individuals (p = 0.029). Individuals with a cysteine substitution in the UMOD gene appeared to have a better prognosis than individuals with other amino acid substitutions (p = 0.015).

A novel likely pathogenic variant in the UMOD gene in a family with autosomal dominant tubulointerstitial kidney disease: a case report

Background

Autosomal dominant tubulointerstitial kidney disease (ADTKD) caused by a pathogenic variant in UMOD (ADTKD-UMOD) is a rare group of diseases characterized by hyperuricaemia with decreased urinary excretion of urate, gout and progressive chronic kidney disease. The mundane clinical characteristics often result in a failure to diagnose ADTKD-UMOD.

Case presentation

In this report, we describe a 12-year-old boy who presented with polyarthritis, hyperuricaemia and tophi with a family history of 8 affected individuals. Clinical data, blood and urine samples of 3 affected members and 8 unaffected members were collected. Genetic testing of the eight genes (UMOD, HPRT1, PRPS1, MTHFR, REN, HNF1b, URAT1 and G6PC) was performed using Sanger sequencing. A heterozygous missense variant (c.674C > G; p.T225R) in UMOD was found in this boy, his older brother with the same phenotype and his mother with hyperuricaemia, gout and chronic kidney disease.

Conclusion

This case highlights the importance of family history and genetic testing for definite diagnosis. This novel variant extends the spectrum of known UMOD gene variants and further supports the allelic heterogeneity of ADTKD-UMOD.

Characterization of mRNA profiles of the exosome-like vesicles in porcine follicular fluid

Extracellular vesicles such as exosomes contain several types of transcripts, including mRNAs and micro RNAs (miRNAs), and have emerged as important mediators of cell-to-cell communication. Exosome-like vesicles were identified in the ovarian follicles of several mammalian species. Although the miRNA contents have been extensively characterized, the detailed investigation of their mRNA profiles is lacking. Here, we characterize the mRNA profiles of exosome-like vesicles in ovarian follicles in a pig model. The mRNA contents of the exosome-like vesicles isolated from porcine follicular fluid were analyzed and compared with those from mural granulosa cells (MGCs) using the Illumina HiSeq platform. Bioinformatics studies suggested that the exosomal mRNAs are enriched in those encoding proteins involved in metabolic, phosphatidylinositol-4,5-bisphosphate 3-kinase (PI3K) -protein kinase B (AKT), and mitogen-activated protein kinase (MAPK) pathways. While the mRNA profile of the exosome-like vesicles resembled that of MGCs, the vesicles contained mRNAs barely detectable in MGCs. Thus, while the majority of the vesicles are likely to be secreted from MGCs, some may originate from other cell types, including theca cells and oocytes, as well as the cells of non-ovarian organs/tissues. Therefore, the mRNA profiles unveiled several novel characteristics of the exosome-like vesicles in ovarian follicles.

Human chorionic gonadotrophin pharmaceutical formulations of urinary origin display high levels of contaminant proteins-A label-free quantitation proteomics study

To determine whether there is a measurable protein background in different formulations of urinary and recombinant human chorionic gonadotropin (hCG). Primary outcome measures: identification of contaminant proteins in urinary-derived formulations of hCG; secondary outcome measures: quantitative values of contaminant proteins in different batches of urinary -derived hCG formulations. It was found that urinary-derived batches have high presence of contaminant proteins beside the active substance. The relative amount of contaminant proteins and hCG differs strongly between different batches.

UMOD gene mutations in Chinese patients with autosomal dominant tubulointerstitial kidney disease: a pediatric case report and literature review

Background

Autosomal dominant tubulointerstitial kidney disease (ADTKD) caused by UMOD gene mutation (ADTKD-UMOD) is rare in children, characterized by hyperuricemia, gout, and progressive chronic kidney disease. It usually leads to end-stage renal failure at fiftieth decades. Here, we report a 3-year-old Chinese boy in an ADTKD family caused by a novel UMOD gene mutation.

Case presentation

A 3-year-old boy was admitted to our hospital because of persistent hematuria. Urinalysis showed BLD 2+ without proteinuria. The serum levels of uric acid, creatinine and electrolytes were normal. No renal cyst or calculus was found by ultrasonography. Renal biopsy was performed and focal and segmental glomerulosclerosis was found in 4 glomeruli among 35 glomeruli examined. His father was found with end-stage renal disease (ESRD) at the age of 29, and renal ultrasound showed several cysts in both kidneys. A novel heterozygous mutation (c.1648G > A,p.V550I) in exon 8 of UMOD gene was identified by whole exome sequencing in the family. SCBC Genome Browser alignment showed that V550 were highly conserved in uromodulin among different species. Software predicted that the mutation is suspected to be harmful. By literature review, there are 12 mutations of UMOD gene in 14 Chinese families including only one pediatric case(a 16-year-old girl).

Conclusions

A novel heterozygous mutation (c.1648G > A,p.V550I) in exon 8 of UMOD gene was found in in a Chinese child case with ADTKD-UMOD, which extends our understanding of UMOD gene mutation spectrum and phenotype of ADTKD-UMOD in children.

Uromodulin-related autosomal-dominant tubulointerstitial kidney disease-pathogenetic insights based on a case

Uromodulin-related autosomal-dominant tubulointerstitial kidney disease (ADTKD-UMOD) is a rare monogenic disorder that is characterized by tubulointerstitial fibrosis and progression of kidney function loss, and may progress to end-stage renal disease. It is usually accompanied by hyperuricaemia and gout. Mutations in the uromodulin gene (UMOD) resulting in malfunctioning of UMOD are known to be the cause of ADTKD-UMOD, which is assumed to be an endoplasmatic reticulum (ER) storage disease. As a case vignette, we report a 29-year-old female with a suspicious family history of chronic kidney disease presenting with progressive loss of renal function, hyperuricaemia and frequent urinary tract infections. Urinary tract infections and pyelonephritides may represent a clinical feature of uromodulin malfunction as it plays a protective role against urinary tract infections despite only sporadic data on this topic. ADTKD-UMOD was diagnosed after genetic testing revealing a missense mutation in the UMOD gene. Light microscopy showed excessive tubular interstitial fibrosis and tubular atrophy together with signs of glomerular sclerosis. Electron microscopic findings could identify electron dense storage deposits in the ER of tubular epithelial cells of the thick ascending loop. Immunohistological staining with KDEL (lysine, aspartic acid, glutamic acid, leucine) showed positivity in the tubular cells, which likely represents ER expansion upon accumulation of misfolded UMOD which could trigger the unfolded protein response and ER stress. This review highlights pathophysiological mechanisms that are subject to ADTKD-UMOD.

A novel uromodulin mutation in autosomal dominant tubulointerstitial kidney disease: a pedigree-based study and literature review

Autosomal dominant tubulointerstitial kidney disease caused by mutations in uromodulin gene (ADTKD-UMOD) is a spectrum of hereditary renal disorders, characterized by early-onset hyperuricemia, gout and progressive nephropathy. This study presented a novel UMOD mutation in an ADTKD pedigree and reviewed studies in Chinese population. The index patient is a 16-year-old girl with hypertension, hyperuricemia and normal serum creatinine level. Four affected and six unaffected members were available for genetic screen. The mutation analysis was performed by next-generation sequencing and direct sequencing. A literature research was conducted to review Chinese ADTKD-UMOD cases. MEDLINE and Chinese Biomedicine Databases were searched with 'uromodulin', 'juvenile gout' and their related terms. Genetic sequencing revealed a de novo mutation within exon 3 (Cys223Gly), which was co-segregating with phenotype in this pedigree. In the review, four studies and our study involving a total of 67 ADTKD patients from 11 families were identified. Of these patients, 27 were confirmed to carry UMOD mutations. Mutations occurred in exon 3 were commonly observed, while mutations within exon 4, 5 and 9 occurred less frequently in Chinese ADTKD-UMOD cases. Among these cases, median age of symptom onset was 26.5 years, median age of end-stage renal diseases (ESRD) or death by ESRD was 41.9 years without renal replacement treatment. Phenotype caused by mutations in D8C domain seemed to be severe than those in GPI domain. Compared with patients of other race, Chinese ADTKD-UMOD patients advanced more aggressively to ESRD.

A single nucleotide polymorphism in the UMOD promoter is associated with end stage renal disease

BACKGROUND

Several genome-wide association studies revealed that several variants of UMOD gene were related to the estimated glomerular filtration rate (eGFR), CKD or hypertension. In this study, we investigated the association between a common variant rs13333226 in the promoter region of UMOD gene and end stage renal disease (ESRD).

METHODS

Variant rs13333226 of UMOD gene was genotyped by using the ABI Real time TaqMan allelic discrimination assay in a case-control study including 638 unrelated patients with ESRD and 366 controls.

RESULTS

The frequency of UMOD SNP rs13333226 GG/GA genotype was significantly higher (36.83% vs. 20.22%, P = 4.02 × 10^-8) and the frequency of G allele was much higher (19.04% vs. 11.20%, P = 4.00 × 10^-6) in the patients with ESRD than in the controls. The G allele was associated with an increased risk of ESRD (odds ratio 2.30, 95% confidence interval 1.70-3.11, P = 6.10 × 10^-8). And G allele (odds ratio 2.33, 95% confidence interval 1.32-4.13, P = 3.65 × 10^-3) was associated independently with ESRD.

CONCLUSIONS

A common variation rs13333226 in the promoter region of UMOD gene was independently associated with ESRD in Han Chinese.

Pathogenic uromodulin mutations result in premature intracellular polymerization

Several renal diseases involve mutations in the gene encoding uromodulin, the predominant protein in urine. We investigated the intracellular processing of wild-type uromodulin, and three mutants: p.V93_G97del/ins AASC; C155R; and C150S. A renal biopsy from a patient harboring the C155R mutation revealed intracellular protein accumulation. Wild-type uromodulin was efficiently trafficked to the cell surface in transfected tsA 201 cells, whereas the mutants were partially retained within the cell, and incompletely processed. Atomic force microscopy imaging revealed that the intracellular mutant proteins contained fibrillar structures similar to urinary uromodulin. We suggest that premature intracellular polymerization underlies the pathology of uromodulin diseases.