Emine Korkmaz

DGKE Variants Cause a Glomerular Microangiopathy That Mimics Membranoproliferative GN

Renal microangiopathies and membranoproliferative GN (MPGN) can manifest similar clinical presentations and histology, suggesting the possibility of a common underlying mechanism in some cases. Here, we performed homozygosity mapping and whole exome sequencing in a Turkish consanguineous family and identified DGKE gene variants as the cause of a membranoproliferative-like glomerular microangiopathy. Furthermore, we identified two additional DGKE variants in a cohort of 142 unrelated patients diagnosed with membranoproliferative GN. This gene encodes the diacylglycerol kinase DGKε, which is an intracellular lipid kinase that phosphorylates diacylglycerol to phosphatidic acid. Immunofluorescence confocal microscopy demonstrated that mouse and rat Dgkε colocalizes with the podocyte marker WT1 but not with the endothelial marker CD31. Patch-clamp experiments in human embryonic kidney (HEK293) cells showed that DGKε variants affect the intracellular concentration of diacylglycerol. Taken together, these results not only identify a genetic cause of a glomerular microangiopathy but also suggest that the phosphatidylinositol cycle, which requires DGKE, is critical to the normal function of podocytes.

Mutations in EMP2 cause childhood-onset nephrotic syndrome.

Nephrotic syndrome (NS) is a genetically heterogeneous group of diseases that are divided into steroid-sensitive NS (SSNS) and steroid-resistant NS (SRNS). SRNS inevitably leads to end-stage kidney disease, and no curative treatment is available. To date, mutations in more than 24 genes have been described in Mendelian forms of SRNS; however, no Mendelian form of SSNS has been described. To identify a genetic form of SSNS, we performed homozygosity mapping, whole-exome sequencing, and multiplex PCR followed by next-generation sequencing. We thereby detected biallelic mutations in EMP2 (epithelial membrane protein 2) in four individuals from three unrelated families affected by SRNS or SSNS. We showed that EMP2 exclusively localized to glomeruli in the kidney. Knockdown of emp2 in zebrafish resulted in pericardial effusion, supporting the pathogenic role of mutated EMP2 in human NS. At the cellular level, we showed that knockdown of EMP2 in podocytes and endothelial cells resulted in an increased amount of CAVEOLIN-1 and decreased cell proliferation. Our data therefore identify EMP2 mutations as causing a recessive Mendelian form of SSNS.

ADCK4-Associated Glomerulopathy Causes Adolescence-Onset FSGS

Hereditary defects of coenzyme Q10 biosynthesis cause steroid-resistant nephrotic syndrome (SRNS) as part of multiorgan involvement but may also contribute to isolated SRNS. Here, we report 26 patients from 12 families with recessive mutations in ADCK4. Mutation detection rate was 1.9% among 534 consecutively screened cases. Patients with ADCK4 mutations showed a largely renal-limited phenotype, with three subjects exhibiting occasional seizures, one subject exhibiting mild mental retardation, and one subject exhibiting retinitis pigmentosa. ADCK4 nephropathy presented during adolescence (median age, 14.1 years) with nephrotic-range proteinuria in 44% of patients and advanced CKD in 46% of patients at time of diagnosis. Renal biopsy specimens uniformly showed FSGS. Whereas 47% and 36% of patients with mutations in WT1 and NPHS2, respectively, progressed to ESRD before 10 years of age, ESRD occurred almost exclusively in the second decade of life in ADCK4 nephropathy. However, CKD progressed much faster during adolescence in ADCK4 than in WT1 and NPHS2 nephropathy, resulting in similar cumulative ESRD rates (>85% for each disorder) in the third decade of life. In conclusion, ADCK4-related glomerulopathy is an important novel differential diagnosis in adolescents with SRNS/FSGS and/or CKD of unknown origin.

Mutations in ANKS6 Cause a Nephronophthisis-Like Phenotype with ESRD

Nephronophthisis (NPHP) is one of the most common genetic causes of CKD; however, the underlying genetic abnormalities have been established in <50% of patients. We performed genome-wide analysis followed by targeted resequencing in a Turkish consanguineous multiplex family and identified a canonic splice site mutation in ANKS6 associated with an NPHP-like phenotype. Furthermore, we identified four additional ANKS6 variants in a cohort of 56 unrelated patients diagnosed with CKD due to nephronophthisis, chronic GN, interstitial nephritis, or unknown etiology. Immunohistochemistry in human embryonic kidney tissue demonstrated that the expression patterns of ANKS6 change substantially during development. Furthermore, we detected increased levels of both total and active β-catenin in precystic tubuli in Han:SPRD Cy/+ rats. Overall, these data indicate the importance of ANKS6 in human kidney development and suggest a mechanism by which mutations in ANKS6 may contribute to an NPHP-like phenotype in humans.

Follow-up results of patients with ADCK4 mutations and the efficacy of CoQ10 treatment

BackgroundADCK4-related glomerulopathy is an important differential diagnosis in adolescents with steroid-resistant nephrotic syndrome (SRNS) and/or chronic kidney disease (CKD) of unknown origin. We screened adolescent patients to determine the frequency of ADCK4 mutation and the efficacy of early CoQ10 administration.MethodsA total of 146 index patients aged 10–18 years, with newly diagnosed non-nephrotic proteinuria, nephrotic syndrome, or chronic renal failure and end-stage kidney disease (ESKD) of unknown etiology were screened for ADCK4 mutation.ResultsTwenty-eight individuals with bi-allelic mutation from 11 families were identified. Median age at diagnosis was 12.4 (interquartile range [IQR] 8.04–19.7) years. Upon first admission, all patients had albuminuria and 18 had CKD (6 ESKD). Eight were diagnosed either through the screening of family members following index case identification or during genetic investigation of proteinuria in an individual with a history of a transplanted sibling. Median age of these 8 patients was 21.5 (range 4.4–39) years. CoQ10 supplementation was administered following genetic diagnosis. Median estimated glomerular filtration rate (eGFR) just before CoQ10 administration was 140 (IQR 117–155) ml/min/1.73m2, proteinuria was 1,008 (IQR 281–1,567) mg/m2/day. After a median follow-up of 11.5 (range 4–21) months following CoQ10 administration, proteinuria was significantly decreased (median 363 [IQR 175–561] mg/m2/day, P=0.025), whereas eGFR was preserved (median 137 [IQR 113–158] ml/min/1.73m2, P=0.61).ConclusionsADCK4 mutations are one of the most common causes of adolescent-onset albuminuria and/or CKD of unknown etiology in Turkey. CoQ10 supplementation appears efficacious at reducing proteinuria, and may thereby be renoprotective.

PW01-004 – The sequence analysis in E148Q homozygous patients

Familial Mediterranean fever (FMF) is an autosomal recessive disease associated with a number of mutations of the MEFV gene. To date 246 variants responsible for the disease were identified, one such a variant is E148Q in exon 2. The role of E148Q variant in the development of FMF remains inconclusive. Some authors believe it causes the disease, whereas others favor the concept of a non causative role.

Familial Mediterranean fever patients homozygous for E148Q variant.

Familial Mediterranean fever (FMF) results from MEFV gene mutations. E148Q is a variant of unknown significance in MEFV. We aimed to define characteristics of FMF patients homozygous for E148Q, check for other MEFV variants in a subgroup, and compare the characteristics with FMF patients carrying other mutations.

Epidermolysis Bullosa with Pyloric Atresia and Aplasia Cutis in a Newborn Due to Homozygous Mutation in ITGB4

ABSTRACT Background: Epidermolysis bullosa with pyloric atresia (EB-PA) is an autosomal recessive disorder due to mutations in ITGA6 and/or ITGB4, resulting in altered expression of α6β4 integrin. EB-PA can also occur with aplasia cutis. Case report: We present a newborn with EB-PA and aplasia cutis, born of consanguineous parents, with a homozygous c.3793+1G>A mutation affecting ITGB4, previously described only in the heterozygous state with other mutations. Conclusion: The previously unreported homozygous c.3793+1G>A mutation affecting ITGB4 causes a severe form of junctional epidermolysis bullosa with pyloric atresia and aplasia cutis.

Hemolytic uremic syndrome and iga nephropathy in a child: coincidence or not?

Sürmeli-Döven S, Delibaş A, Gürses İ, Kayacan UR, Coşkun-Yılmaz B, Esen K, Korkmaz E, Özaltın F. Hemolytic uremic syndrome and IgA nephropathy in a child: Coincidence or not? Turk J Pediatr 2018; 60: 81-85. A previously healthy 18-month old boy, presenting with diarrhea, anemia, thrombocytopenia and acute renal failure was admitted to our hospital. Hemolytic uremic syndrome (HUS) was diagnosed with his clinical and laboratory findings. His stool was negative for Shiga toxin producing E. coli (STEC). During follow-up he developed respiratory distress, hypertrophic cardiomyopathy and seizure. His genetic tests for atypical HUS (aHUS) were negative. His clinical and histological findings indicated hemolytic uremic syndrome and immunglobulin A nephropathy (IgAN). The patient responded to steroid treatment and plasma exchange therapy with peritoneal dialysis. We discuss the probable connection between HUS and IgAN.

Atypical Hemolytic Uremic Syndrome in Children Aged <2 Years

Background: There are limited data on infants with atypical hemolytic uremic syndrome (aHUS). The aim of this study was to determine the clinical and laboratory features, and to evaluate treatment modalities and outcomes in infants with aHUS. Materials and Methods: Relevant data on patients with onset of aHUS at age <2 years were obtained from the Turkish Pediatric aHUS Registry. Results: Among the 146 patients included in the Registry, 53 (36%) (23 male and 30 female) were enrolled for the study. Age at disease onset was ≤1 year in 29 of the patients. In all, 21 (40%) of the patients developed neurological symptoms. Disease-causing mutations were noted in 14 (36%) of the 39 patients in which genetic analysis was performed. Plasma therapy was performed in 42 (79%) patients; eculizumab therapy was administered to treat the first episode of aHUS in 33 (62%) patients and in 5 patients as the first- line therapy. In total, 38 (72%) patients received renal replacement therapy (RRT), 3 (6%) died due to acute illness, and 4 (8%) were discharged from hospital with RRT. Follow-up visit data were available for 46 patients and the median duration was 23 months (range 3–129 months). End-stage renal disease developed only in 1 patient. Proteinuria and hypertension persisted in 17 (37%) and 20 patients (44%) respectively. Eculizumab treatment was continued in 25 of the 39 patients during the follow-up period. Conclusion: One-third of the aHUS patients had disease onset during infancy. The prognosis of this life-threatening disease seems to get better with improved treatment modalities.