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.

Influence of glycoprotein MUC1 on trafficking of the Ca2+-selective ion channels, TRPV5 and TRPV6, and on in vivo calcium homeostasis.

Polymorphism of the gene encoding mucin 1 (MUC1) is associated with skeletal and dental phenotypes in human genomic studies. Animals lacking MUC1 exhibit mild reduction in bone density. These phenotypes could be a consequence of modulation of bodily Ca homeostasis by MUC1, as suggested by the previous observation that MUC1 enhances cell surface expression of the Ca2+-selective channel, TRPV5, in cultured unpolarized cells. Using biotinylation of cell surface proteins, we asked whether MUC1 influences endocytosis of TRPV5 and another Ca2+-selective TRP channel, TRPV6, in cultured polarized epithelial cells. Our results indicate that MUC1 reduces endocytosis of both channels, enhancing cell surface expression. Further, we found that mice lacking MUC1 lose apical localization of TRPV5 and TRPV6 in the renal tubular and duodenal epithelium. Females, but not males, lacking MUC1 exhibit reduced blood Ca2+. However, mice lacking MUC1 exhibited no differences in basal urinary Ca excretion or Ca retention in response to PTH receptor signaling, suggesting compensation by transport mechanisms independent of TRPV5 and TRPV6. Finally, humans with autosomal dominant tubulointerstitial kidney disease due to frame-shift mutation of MUC1 (ADTKD-MUC1) exhibit reduced plasma Ca concentrations compared to control individuals with mutations in the gene encoding uromodulin (ADTKD-UMOD), consistent with MUC1 haploinsufficiency causing reduced bodily Ca2+. In summary, our results provide further insight into the role of MUC1 in Ca2+-selective TRP channel endocytosis and the overall effects on Ca concentrations.

Autosomal dominant ApoA4 mutations present as tubulointerstitial kidney disease with medullary amyloidosis.

Sporadic cases of apolipoprotein A-IV medullary amyloidosis have been reported. Here we describe five families found to have autosomal dominant medullary amyloidosis due to two different pathogenic APOA4 variants. A large family with autosomal dominant chronic kidney disease (CKD) and bland urinary sediment underwent whole genome sequencing with identification of a chr11:116692578 G>C (hg19) variant encoding the missense mutation p.L66V of the ApoA4 protein. We identified two other distantly related families from our registry with the same variant and two other distantly related families with a chr11:116693454 C>T (hg19) variant encoding the missense mutation p.D33N. Both mutations are unique to affected families, evolutionarily conserved and predicted to expand the amyloidogenic hotspot in the ApoA4 structure. Clinically affected individuals suffered from CKD with a bland urinary sediment and a mean age for kidney failure of 64.5 years. Genotyping identified 48 genetically affected individuals; 44 individuals had an estimated glomerular filtration rate (eGFR) under 60 ml/min/1.73 m2, including all 25 individuals with kidney failure. Significantly, 11 of 14 genetically unaffected individuals had an eGFR over 60 ml/min/1.73 m2. Fifteen genetically affected individuals presented with higher plasma ApoA4 concentrations. Kidney pathologic specimens from four individuals revealed amyloid deposits limited to the medulla, with the mutated ApoA4 identified by mass-spectrometry as the predominant amyloid constituent in all three available biopsies. Thus, ApoA4 mutations can cause autosomal dominant medullary amyloidosis, with marked amyloid deposition limited to the kidney medulla and presenting with autosomal dominant CKD with a bland urinary sediment. Diagnosis relies on a careful family history, APOA4 sequencing and pathologic studies.

Autosomal dominant tubulointerstitial kidney disease: A review.

The clinical characteristics of autosomal dominant tubulointerstitial kidney disease (ADTKD) include bland urinary sediment, slowly progressive chronic kidney disease (CKD) with many patients reaching end stage renal disease (ESRD) between age 20 and 70 years, and autosomal dominant inheritance. Due to advances in genetic diagnosis, ADTKD is becoming increasingly recognized as a cause of CKD. Pathogenic variants in UMOD, MUC1, and REN are the most common causes of ADTKD. ADTKD-UMOD is also associated with hyperuricemia and gout. ADTKD-REN often presents in childhood with mild hypotension, CKD, hyperkalemia, acidosis, and anemia. ADTKD-MUC1 patients present only with CKD. This review describes the pathophysiology, genetics, clinical manifestation, and diagnosis for ADTKD, with an emphasis on genetic testing and genetic counseling suggestions for patients.

Autosomal dominant tubulointerstitial kidney disease: more than just HNF1ß.

Autosomal dominant tubulointerstitial kidney disease (ADTKD) refers to a group of disorders with a bland urinary sediment, slowly progressive chronic kidney disease (CKD), and autosomal dominant inheritance. Due to advances in genetic diagnosis, ADTKD is becoming increasingly recognized as a cause of CKD in both children and adults. ADTKD-REN presents in childhood with mild hypotension, CKD, hyperkalemia, acidosis, and anemia. ADTKD-UMOD is associated with gout and CKD that may present in adolescence and slowly progresses to kidney failure. HNF1ß mutations often present in childhood with anatomic abnormalities such as multicystic or dysplastic kidneys, as well as CKD and a number of other extra-kidney manifestations. ADTKD-MUC1 is less common in childhood, and progressive CKD is its sole clinical manifestation, usually beginning in the late teenage years. This review describes the pathophysiology, genetics, clinical characteristics, diagnosis, and treatment of the different forms of ADTKD, with an emphasis on diagnosis. We also present data on kidney function in children with ADTKD from the Wake Forest Rare Inherited Kidney Disease Registry.

Ultrabright plasmonic fluor nanolabel-enabled detection of a urinary ER stress biomarker in autosomal dominant tubulointerstitial kidney disease.

Autosomal dominant tubulointerstitial kidney disease (ADTKD)-uromodulin (UMOD) is the most common nonpolycystic genetic kidney disease, but it remains unrecognized due to its clinical heterogeneity and lack of screening test. Moreover, the fact that the clinical feature is a poor predictor of disease outcome further highlights the need for the development of mechanistic biomarkers in ADTKD. However, low abundant urinary proteins secreted by thick ascending limb cells, where UMOD is synthesized, have posed a challenge for the detection of biomarkers in ADTKD-UMOD. In the CRISPR/Cas9-generated murine model and patients with ADTKD-UMOD, we found that immunoglobulin heavy chain-binding protein (BiP), an endoplasmic reticulum chaperone, was exclusively upregulated by mutant UMOD in the thick ascending limb and easily detected by Western blot analysis in the urine at an early stage of disease. However, even the most sensitive ELISA failed to detect urinary BiP in affected individuals. We therefore developed an ultrasensitive, plasmon-enhanced fluorescence-linked immunosorbent assay (p-FLISA) to quantify urinary BiP concentration by harnessing the newly invented ultrabright fluorescent nanoconstruct, termed "plasmonic Fluor." p-FLISA demonstrated that urinary BiP excretion was significantly elevated in patients with ADTKD-UMOD compared with unaffected controls, which may have potential utility in risk stratification, disease activity monitoring, disease progression prediction, and guidance of endoplasmic reticulum-targeted therapies in ADTKD.NEW & NOTEWORTHY Autosomal dominant tubulointerstitial kidney disease (ADTKD)-uromodulin (UMOD) is an underdiagnosed cause of chronic kidney disease (CKD). Lack of ultrasensitive bioanalytical tools has hindered the discovery of low abundant urinary biomarkers in ADTKD. Here, we developed an ultrasensitive plasmon-enhanced fluorescence-linked immunosorbent assay (p-FLISA). p-FLISA demonstrated that secreted immunoglobulin heavy chain-binding protein is an early urinary endoplasmic reticulum stress biomarker in ADTKD-UMOD, which will be valuable in monitoring disease progression and the treatment response in ADTKD.

Plasma Mucin-1 (CA15-3) Levels in Autosomal Dominant Tubulointerstitial Kidney Disease due to MUC1 Mutations.

INTRODUCTION: Patients with ADTKD-MUC1 have one allele producing normal mucin-1 (MUC1) and one allele producing mutant MUC1, which remains intracellular. We hypothesized that ADTKD-MUC1 patients, who have only 1 secretory-competent wild-type MUC1 allele, should exhibit decreased plasma mucin-1 (MUC1) levels. To test this hypothesis, we repurposed the serum CA15-3 assay used to measure MUC1 in breast cancer to measure plasma MUC1 levels in ADTKD-MUC1. METHODS: This cross-sectional study analyzed CA15-3 levels in a reference population of 6,850 individuals, in 85 individuals with ADTKD-MUC1, and in a control population including 135 individuals with ADTKD-UMOD and 114 healthy individuals. RESULTS: Plasma CA15-3 levels (mean ± standard deviation) were 8.6 ± 4.3 U/mL in individuals with ADTKD-MUC1 and 14.6 ± 5.6 U/mL in controls (p < 0.001). While there was a significant difference in mean CA15-3 levels, there was substantial overlap between the 2 groups. Plasma CA15-3 levels were <5 U/mL in 22% of ADTKD-MUC1 patients, in 0/249 controls, and in 1% of the reference population. Plasma CA15-3 levels were >20 U/mL in 1/85 ADTKD-MUC1 patients, in 18% of control individuals, and in 25% of the reference population. Segregation of plasma CA15-3 levels by the rs4072037 genotype did not significantly improve differentiation between affected and unaffected individuals. CA15-3 levels were minimally affected by gender and estimated glomerular filtration rate. DISCUSSION/CONCLUSIONS: Plasma CA15-3 levels in ADTKD-MUC1 patients are approximately 40% lower than levels in healthy individuals, though there is significant overlap between groups. Further investigations need to be performed to see if plasma CA15-3 levels would be useful in diagnosis, prognosis, or assessing response to new therapies in this disorder.

Clinical and genetic spectra of autosomal dominant tubulointerstitial kidney disease due to mutations in UMOD and MUC1.

Autosomal dominant tubulointerstitial kidney disease (ADTKD) is an increasingly recognized cause of end-stage kidney disease, primarily due to mutations in UMOD and MUC1. The lack of clinical recognition and the small size of cohorts have slowed the understanding of disease ontology and development of diagnostic algorithms. We analyzed two registries from Europe and the United States to define genetic and clinical characteristics of ADTKD-UMOD and ADTKD-MUC1 and develop a practical score to guide genetic testing. Our study encompassed 726 patients from 585 families with a presumptive diagnosis of ADTKD along with clinical, biochemical, genetic and radiologic data. Collectively, 106 different UMOD mutations were detected in 216/562 (38.4%) of families with ADTKD (303 patients), and 4 different MUC1 mutations in 72/205 (35.1%) of the families that are UMOD-negative (83 patients). The median kidney survival was significantly shorter in patients with ADTKD-MUC1 compared to ADTKD-UMOD (46 vs. 54 years, respectively), whereas the median gout-free survival was dramatically reduced in patients with ADTKD-UMOD compared to ADTKD-MUC1 (30 vs. 67 years, respectively). In contrast to patients with ADTKD-UMOD, patients with ADTKD-MUC1 had normal urinary excretion of uromodulin and distribution of uromodulin in tubular cells. A diagnostic algorithm based on a simple score coupled with urinary uromodulin measurements separated patients with ADTKD-UMOD from those with ADTKD-MUC1 with a sensitivity of 94.1%, a specificity of 74.3% and a positive predictive value of 84.2% for a UMOD mutation. Thus, ADTKD-UMOD is more frequently diagnosed than ADTKD-MUC1, ADTKD subtypes present with distinct clinical features, and a simple score coupled with urine uromodulin measurements may help prioritizing genetic testing.

An international cohort study of autosomal dominant tubulointerstitial kidney disease due to REN mutations identifies distinct clinical subtypes.

There have been few clinical or scientific reports of autosomal dominant tubulointerstitial kidney disease due to REN mutations (ADTKD-REN), limiting characterization. To further study this, we formed an international cohort characterizing 111 individuals from 30 families with both clinical and laboratory findings. Sixty-nine individuals had a REN mutation in the signal peptide region (signal group), 27 in the prosegment (prosegment group), and 15 in the mature renin peptide (mature group). Signal group patients were most severely affected, presenting at a mean age of 19.7 years, with the prosegment group presenting at 22.4 years, and the mature group at 37 years. Anemia was present in childhood in 91% in the signal group, 69% prosegment, and none of the mature group. REN signal peptide mutations reduced hydrophobicity of the signal peptide, which is necessary for recognition and translocation across the endoplasmic reticulum, leading to aberrant delivery of preprorenin into the cytoplasm. REN mutations in the prosegment led to deposition of prorenin and renin in the endoplasmic reticulum-Golgi intermediate compartment and decreased prorenin secretion. Mutations in mature renin led to deposition of the mutant prorenin in the endoplasmic reticulum, similar to patients with ADTKD-UMOD, with a rate of progression to end stage kidney disease (63.6 years) that was significantly slower vs. the signal (53.1 years) and prosegment groups (50.8 years) (significant hazard ratio 0.367). Thus, clinical and laboratory studies revealed subtypes of ADTKD-REN that are pathophysiologically, diagnostically, and clinically distinct.

Outcomes of patient self-referral for the diagnosis of several rare inherited kidney diseases.

PURPOSE: To evaluate self-referral from the Internet for genetic diagnosis of several rare inherited kidney diseases. METHODS: Retrospective study from 1996 to 2017 analyzing data from an academic referral center specializing in autosomal dominant tubulointerstitial kidney disease (ADTKD). Individuals were referred by academic health-care providers (HCPs) nonacademic HCPs, or directly by patients/families. RESULTS: Over 21 years, there were 665 referrals, with 176 (27%) directly from families, 269 (40%) from academic HCPs, and 220 (33%) from nonacademic HCPs. Forty-two (24%) direct family referrals had positive genetic testing versus 73 (27%) families from academic HCPs and 55 (25%) from nonacademic HCPs (P = 0.72). Ninety-nine percent of direct family contacts were white and resided in zip code locations with a mean median income of $77,316 ± 34,014 versus US median income $49,445. CONCLUSION: Undiagnosed families with Internet access bypassed their physicians and established direct contact with an academic center specializing in inherited kidney disease to achieve a diagnosis. Twenty-five percent of all families diagnosed with ADTKD were the result of direct family referral and would otherwise have been undiagnosed. If patients suspect a rare disorder that is undiagnosed by their physicians, actively pursuing self-diagnosis using the Internet can be successful. Centers interested in rare disorders should consider improving direct access to families.

Utility of Genomic Testing after Renal Biopsy.

BACKGROUND: Renal biopsy is the mainstay of renal pathological diagnosis. Despite sophisticated diagnostic techniques, it is not always possible to make a precise pathological diagnosis. Our aim was to identify a genetic cause of disease in patients who had undergone renal biopsy and determine if genetic testing altered diagnosis or treatment. METHODS: Patients with suspected familial kidney disease underwent a variety of next-generation sequencing (NGS) strategies. The subset of these patients who had also undergone native kidney biopsy was identified. Histological specimens were reviewed by a consultant pathologist, and genetic and pathological diagnoses were compared. RESULTS: Seventy-five patients in 47 families underwent genetic sequencing and renal biopsy. Patients were grouped into 5 diagnostic categories based on pathological diagnosis: tubulointerstitial kidney disease (TIKD; n = 18); glomerulonephritis (GN; n = 15); focal segmental glomerulosclerosis and Alport Syndrome (n = 11); thrombotic microangiopathy (TMA; n = 17); and nonspecific pathological changes (n = 14). Thirty-nine patients (52%) in 21 families (45%) received a genetic diagnosis; 13 cases (72%) with TIKD, 4 (27%) with GN, 6 (55%) with focal segmental glomerulosclerosis/Alport syndrome, and 10 (59%) with TMA and 6 cases (43%) with nonspecific features. Genetic testing resulted in changes in understanding of disease mechanism in 21 individuals (54%) in 12 families (57%). Treatment would have been altered in at least 26% of cases (10/39). CONCLUSIONS: An accurate genetic diagnosis can result in changes in clinical diagnosis, understanding of pathological mechanism, and treatment. NGS should be considered as a complementary diagnostic technique to kidney biopsy in the evaluation of patients with kidney disease.

Renal transplant outcomes in patients with autosomal dominant tubulointerstitial kidney disease.

INTRODUCTION: Autosomal dominant tubulointerstitial kidney disease (ADTKD) is a rare genetic cause of chronic kidney disease (CKD) and end-stage renal disease (ESRD). We aimed to compare renal transplant outcomes in people with ESRD due to ADTKD to those with other causes of renal failure. METHODS: Patients with clinical characteristics consistent with ADTKD by the criteria outlined in the 2015 KDIGO consensus were included. We compared ADTKD transplant outcomes with those of 4633 non-ADTKD renal transplant recipients. RESULTS: We included 31 patients who met diagnostic criteria for ADTKD in this analysis, 23 of whom had an identified mutation (28 were categorized as definite-ADTKD and 3 as suspected ADTKD). Five patients received a second transplant during follow-up. In total, 36 grafts were included. We did not identify significant differences between groups in terms of graft or patient survival after transplantation. Twenty-five transplant biopsies were performed during follow-up, and none of these showed signs of recurrent ADTKD post-transplant. CONCLUSION: In patients with ESRD due to ADTKD, we demonstrate that transplant outcomes are comparable with the general transplant population. There is no evidence that ADTKD can recur after transplantation.

Heterozygous Loss-of-Function SEC61A1 Mutations Cause Autosomal-Dominant Tubulo-Interstitial and Glomerulocystic Kidney Disease with Anemia.

Autosomal-dominant tubulo-interstitial kidney disease (ADTKD) encompasses a group of disorders characterized by renal tubular and interstitial abnormalities, leading to slow progressive loss of kidney function requiring dialysis and kidney transplantation. Mutations in UMOD, MUC1, and REN are responsible for many, but not all, cases of ADTKD. We report on two families with ADTKD and congenital anemia accompanied by either intrauterine growth retardation or neutropenia. Ultrasound and kidney biopsy revealed small dysplastic kidneys with cysts and tubular atrophy with secondary glomerular sclerosis, respectively. Exclusion of known ADTKD genes coupled with linkage analysis, whole-exome sequencing, and targeted re-sequencing identified heterozygous missense variants in SEC61A1-c.553A>G (p.Thr185Ala) and c.200T>G (p.Val67Gly)-both affecting functionally important and conserved residues in SEC61. Both transiently expressed SEC6A1A variants are delocalized to the Golgi, a finding confirmed in a renal biopsy from an affected individual. Suppression or CRISPR-mediated deletions of sec61al2 in zebrafish embryos induced convolution defects of the pronephric tubules but not the pronephric ducts, consistent with the tubular atrophy observed in the affected individuals. Human mRNA encoding either of the two pathogenic alleles failed to rescue this phenotype as opposed to a complete rescue by human wild-type mRNA. Taken together, these findings provide a mechanism by which mutations in SEC61A1 lead to an autosomal-dominant syndromic form of progressive chronic kidney disease. We highlight protein translocation defects across the endoplasmic reticulum membrane, the principal role of the SEC61 complex, as a contributory pathogenic mechanism for ADTKD.

A randomized trial of vonapanitase (PATENCY-1) to promote radiocephalic fistula patency and use for hemodialysis.

OBJECTIVE: Arteriovenous fistulas created in patients with chronic kidney disease often lose patency and fail to become usable. This prospective trial evaluated the efficacy of vonapanitase, a recombinant human elastase, in promoting radiocephalic fistula patency and use for hemodialysis. METHODS: PATENCY-1 was a double-blind, placebo-controlled trial that enrolled 349 patients on or approaching hemodialysis and being evaluated for radiocephalic arteriovenous fistula creation. Of these, 313 were randomized and 311 treated. Patients were assigned to vonapanitase (n = 210) or placebo (n = 103). The study drug solution was applied topically to the artery and vein for 10 minutes immediately after fistula creation. The primary and secondary end points were primary patency (time to first thrombosis or corrective procedure) and secondary patency (time to abandonment). Tertiary end points included use of the fistula for hemodialysis, fistula maturation by ultrasound, and procedure rates. RESULTS: The Kaplan-Meier estimates of 12-month primary patency were 42% (95% confidence interval [CI], 35-49) and 31% (95% CI, 21-42) for vonapanitase and placebo (P = .25). The Kaplan-Meier estimates of 12-month secondary patency were 74% (95% CI, 68-80) and 61% (95% CI, 51-71) for vonapanitase and placebo (P = .048). The proportions of vonapanitase and placebo patients were 39% and 25% (P = .035) with unassisted use for hemodialysis and 64% and 44% (P = .006) with unassisted plus assisted use. CONCLUSIONS: Vonapanitase treatment did not significantly improve primary patency but was associated with increased secondary patency and use for hemodialysis. Further research is needed to evaluate these end points.

Quality of life in patients with autosomal dominant tubulointerstitial kidney disease
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AIMS: The reaction to diagnosis and quality of life (QOL) in autosomal dominant tubulointerstitial kidney disease (ADTKD) due to UMOD and MUC mutations from the time of diagnosis until treatment for end-stage kidney disease (ESKD) has not been characterized. It is unclear how asymptomatic patients react to a positive genetic test result. MATERIALS AND METHODS: A cross-sectional survey concerning QOL and genetic testing was delivered to 622 individuals who had undergone genetic testing from families with known ADTKD. RESULTS: 286 of 622 individuals completed the survey, including 61 (21%) genetically unaffected, 36 (12%) with stage 1, 2 chronic kidney disease (CKD), 51 (18%) stage 3, 41 (14%) stage 4 pre-dialysis, 50 (17%) receiving dialysis, and 47 (16%) s/p kidney transplantation. Of 55 respondents who thought they had normal kidney function at the time of testing and were found to have ADTKD, 51 (93%) were happy testing was performed, 3 (5%) neutral, and 1 (2%) neutral/unhappy. 42 of 183 (23%) affected individuals stated that ADTKD "has a substantial effect and I think about it daily," 47 (26%) think about ADTKD weekly, 48 (26%) monthly, and 48 (26%) less than monthly. The mean PROMIS anxiety score was similar between unaffected and affected individuals and the general population. Depression was present in 41% of affected vs. 23% of unaffected individuals (p = 0.01). CONCLUSION: Genetic testing of presymptomatic patients for ADTKD is reasonable when requested. This study provides reassurance regarding the impact on QOL of the increased use of genetic testing to diagnose kidney disease. ADTKD has a significant impact on QOL, with depression, not anxiety, being more prevalent in affected individuals.

Noninvasive Immunohistochemical Diagnosis and Novel MUC1 Mutations Causing Autosomal Dominant Tubulointerstitial Kidney Disease.

BACKGROUND: Autosomal dominant tubulointerstitial kidney disease caused by mucin-1 gene (MUC1) mutations (ADTKD-MUC1) is characterized by progressive kidney failure. Genetic evaluation for ADTKD-MUC1 specifically tests for a cytosine duplication that creates a unique frameshift protein (MUC1fs). Our goal was to develop immunohistochemical methods to detect the MUC1fs created by the cytosine duplication and, possibly, by other similar frameshift mutations and to identify novel MUC1 mutations in individuals with positive immunohistochemical staining for the MUC1fs protein. METHODS: We performed MUC1fs immunostaining on urinary cell smears and various tissues from ADTKD-MUC1-positive and -negative controls as well as in individuals from 37 ADTKD families that were negative for mutations in known ADTKD genes. We used novel analytic methods to identify MUC1 frameshift mutations. RESULTS: After technique refinement, the sensitivity and specificity for MUC1fs immunostaining of urinary cell smears were 94.2% and 88.6%, respectively. Further genetic testing on 17 families with positive MUC1fs immunostaining revealed six families with five novel MUC1 frameshift mutations that all predict production of the identical MUC1fs protein. CONCLUSIONS: We developed a noninvasive immunohistochemical method to detect MUC1fs that, after further validation, may be useful in the future for diagnostic testing. Production of the MUC1fs protein may be central to the pathogenesis of ADTKD-MUC1.

Acadian variant of Fanconi syndrome is caused by mitochondrial respiratory chain complex I deficiency due to a non-coding mutation in complex I assembly factor NDUFAF6.

The Acadian variant of Fanconi Syndrome refers to a specific condition characterized by generalized proximal tubular dysfunction from birth, slowly progressive chronic kidney disease and pulmonary interstitial fibrosis. This condition occurs only in Acadians, a founder population in Nova Scotia, Canada. The genetic and molecular basis of this disease is unknown. We carried out whole exome and genome sequencing and found that nine affected individuals were homozygous for the ultra-rare non-coding variant chr8:96046914 T > C; rs575462405, whereas 13 healthy siblings were either heterozygotes or lacked the mutant allele. This variant is located in intron 2 of NDUFAF6 (NM_152416.3; c.298-768 T > C), 37 base pairs upstream from an alternative splicing variant in NDUFAF6 chr8:96046951 A > G; rs74395342 (c.298-731 A > G). NDUFAF6 encodes NADH:ubiquinone oxidoreductase complex assembly factor 6, also known as C8ORF38. We found that rs575462405-either alone or in combination with rs74395342-affects splicing and synthesis of NDUFAF6 isoforms. Affected kidney and lung showed specific loss of the mitochondria-located NDUFAF6 isoform and ultrastructural characteristics of mitochondrial dysfunction. Accordingly, affected tissues had defects in mitochondrial respiration and complex I biogenesis that were corrected with NDUFAF6 cDNA transfection. Our results demonstrate that the Acadian variant of Fanconi Syndrome results from mitochondrial respiratory chain complex I deficiency. This information may be used in the diagnosis and prevention of this disease in individuals and families of Acadian descent and broadens the spectrum of the clinical presentation of mitochondrial diseases, respiratory chain defects and defects of complex I specifically.

Chronic tubulointerstitial kidney disease in untreated adenine phosphoribosyl transferase (APRT) deficiency: A case report
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Adenine phosphoribosyltransferase (APRT) deficiency (OMIM #614723) is a rare autosomal recessive defect in the purine salvage pathway that causes excessive production of 2,8-dihydroxyadenine, leading to nephrolithiasis and chronic kidney disease (CKD). This case report describes the natural history of CKD in untreated APRT deficiency. We describe a novel APRT mutation (chr16:88877985 G / C; c.195 C>/G; p.His54Asp) presenting with CKD without nephrolithiasis. The patient initially required dialysis, but kidney function improved with allopurinol. We reviewed APRT deficiency reported in the literature to determine the loss of kidney function in individuals with untreated APRT deficiency and its relationship to nephrolithiasis. We identified 95 individuals in whom kidney function was assessed prior to treatment. There was a bimodal distribution of kidney failure. AKI occurred frequently in childhood due to obstructing nephrolithiasis or crystalline nephropathy and was usually reversible. CKD developed after age 20 in all patients irrespective of nephrolithiasis history, with 36/42 patients > 40 years of age having at least stage 3 CKD, and 24/42 having an eGFR > 10 mL/min/1.73m2 or being on dialysis. There were 13 adults without nephrolithiasis and 50 adults with nephrolithiasis. The mean age of end-stage renal diesease (ESRD) was 50.52 ± 13.9 for those without nephrolithiasis and 43.4 ± 15.8 years for those with nephrolithiasis (p = 0.24). APRT deficiency is associated with slowly progressive CKD that occurs independently of nephrolithiasis. Diagnosis should be considered in all individuals with chronic tubulointerstitial kidney disease, with or without the presence of nephrolithiasis. In our patient, allopurinol 300 mg/day resulted in improvement of kidney function.
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Description of a New Simple and Cost-Effective Molecular Testing That Could Simplify MUC1 Variant Detection.

Introduction: Patients with autosomal dominant tubulointerstitial kidney disease (ADTKD) usually present with nonspecific progressive chronic kidney disease (CKD) with mild to negative proteinuria and a family history. ADTKD-MUC1 leads to the formation of a frameshift protein that accumulates in the cytoplasm, leading to tubulointerstitial damage. ADTKD-MUC1 prevalence remains unclear because MUC1 variants are not routinely detected by standard next-generation sequencing (NGS) techniques. Methods: We developed a bioinformatic counting script that can detect specific genetic sequences and count the number of occurrences. We used DNA samples from 27 patients for validation, 11 of them were patients from the Lille University Hospital in France and 16 were from the Wake Forest Hospital, NC. All patients from Lille were tested with an NGS gene panel with our script and all patients from Wake Forest Hospital were tested with the snapshot reference technique. Between January 2018 and February 2023, we collected data on all patients diagnosed with MUC1 variants with this script. Results: A total of 27 samples were tested anonymously by the BROAD Institute reference technique for confirmation and we were able to get a 100% concordance for MUC1 diagnosis. Clinico-biologic characteristics in our cohort were similar to those previously described in ADTKD-MUC1. Conclusion: We describe a new simple and cost-effective method for molecular testing of ADTKD-MUC1. Genetic analyses in our cohort suggest that MUC1 might be the first cause of ADTKD. Increasing the availability of MUC1 diagnosis tools will contribute to a better understanding of the disease and to the development of specific treatments.