Rezan Topaloglu

Mutation frequency of Familial Mediterranean Fever and evidence for a high carrier rate in the Turkish population

Familial Mediterranean Fever (FMF) is a recessive disorder characterised by episodes of fever and neutrophil-mediated serozal inflammation. The FMF gene (MEFV) was recently identified and four common mutations characterised. The aim of this study was to determine the carrier rate in the Turkish population and the mutation frequency in the clinically diagnosed FMF patients. We found a high frequency of carriers in the healthy Turkish population (20%). The distribution of the five most common MEFV mutations among healthy individuals (M694V 3%, M680I 5%, V726A 2%, M694I 0% and E148Q 12%) was significantly different (P<0.005) from that found in patients (M694V 51.55%, M680I 9.22%, V726A 2.88%, M694I 0.44% and E148Q 3.55%).

COQ6 mutations in human patients produce nephrotic syndrome with sensorineural deafness

Steroid-resistant nephrotic syndrome (SRNS) is a frequent cause of end-stage renal failure. Identification of single-gene causes of SRNS has generated some insights into its pathogenesis; however, additional genes and disease mechanisms remain obscure, and SRNS continues to be treatment refractory. Here we have identified 6 different mutations in coenzyme Q10 biosynthesis monooxygenase 6 (COQ6) in 13 individuals from 7 families by homozygosity mapping. Each mutation was linked to early-onset SRNS with sensorineural deafness. The deleterious effects of these human COQ6 mutations were validated by their lack of complementation in coq6-deficient yeast. Furthermore, knockdown of Coq6 in podocyte cell lines and coq6 in zebrafish embryos caused apoptosis that was partially reversed by coenzyme Q10 treatment. In rats, COQ6 was located within cell processes and the Golgi apparatus of renal glomerular podocytes and in stria vascularis cells of the inner ear, consistent with an oto-renal disease phenotype. These data suggest that coenzyme Q10-related forms of SRNS and hearing loss can be molecularly identified and potentially treated.

E148Q is a disease-causing MEFV mutation: a phenotypic evaluation in patients with familial Mediterranean fever

Background: Familial Mediterranean fever (FMF) is one of the periodic fever syndromes. It is common among Turks, Jews, Arabs, and Armenians. Several mutations in the MEFV gene, including E148Q, have been identified as causing this disease. It has been suggested that the E148Q mutation is the mildest mutation and some reports have questioned its disease association. Objective: To evaluate the phenotypic features of the patients with E148Q mutation. Subjects: 26 patients homozygous for E148Q, 10 compound heterozygous for E148Q, and eight complex cases were assessed. Results: Although four of the 26 patients with E148Q/E148Q were asymptomatic at the time of evaluation, abdominal pain was seen in 77% of the patients, fever in 66%, arthralgia in 50%, arthritis in 15.4%, and vomiting in 23.8%. Compound heterozygotes and complex cases had a higher frequency of abdominal pain, fever, arthralgia, arthritis, myalgia, and chest pain than subjects who were homozygous for E148Q, but none of these symptoms reached statistical significance. None of our patients had amyloidosis but two with E148Q/E148Q had a family history of amyloidosis and one had rapidly progressive glomerulonephritis secondary to vasculitis, which progressed to chronic renal failure. Conclusions: Patients homozygous for E148Q have a heterogeneous clinical presentation. Most are symptomatic and colchicine treatment is required in these patients.

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.

MEFV mutations in systemic onset juvenile idiopathic arthritis

OBJECTIVES Autoinflammatory diseases constitute a large spectrum of monogenic diseases like FMF or cryopyrin-associated periodic syndromes (CAPS) and complex genetic trait diseases such as systemic onset juvenile idiopathic arthritis (SoJIA). An increased rate of MEFV mutations has been shown among patients with PAN and HSP, in populations where FMF is frequent. The aim of the study is to search for MEFV mutations in our patients with SoJIA and see whether these mutations had an effect on disease course or complications. METHODS Thirty-five children with the diagnosis of SoJIA were screened for 12 MEFV mutations. The control data were obtained from a previous study of our centre determining the carrier frequency in Turkish population. RESULTS Two patients were homozygous and three patients were heterozygous for the M694V mutation. One patient was a compound heterozygote for the M680I/V726A mutations. Heterozygous V726A mutation was found in one patient. The overall mutation frequency of patients was 14.28%. This figure had been compared with the previously published rate of disease-causing mutations in this country, which is 5%. Disease-causing mutations were found to be significantly more frequent in the SoJIA patients than the population (P < 0.01). Among these, M694V was the leading mutation with a frequency of 10% in SoJIA. Six patients carrying MEFV mutations were among the most resistant cases requiring biological therapy. CONCLUSION SoJIA patients had a significantly higher frequency of MEFV mutations but clinical studies with large number of patients are needed to confirm the association of MEFV mutations with SoJIA and its course.

Hyperimmunoglobulinemia D and periodic fever syndrome; treatment with etanercept and follow-up

The hyperimmunoglobulinemia D and periodic fever syndrome (HIDS) is an autoinflammatory syndrome. It is caused by the mutations of the mevalonate kinase gene. There is no consensus for specific therapy of HIDS, but there are some case reports and studies in regards to its treatment with drugs like colchicine, steroids, nonsteroid anti-inflammatory drugs, simvastatin, anakinra, thalidomide, and etanercept. We are reporting a case evaluated for the complaints of abdominal pain and febrile episodes with massive hepatomegaly, not common finding on physical examination, its treatment with etanercept, and long-term follow-up.

Biallelic hypomorphic mutations in a linear deubiquitinase define otulipenia, an early-onset autoinflammatory disease

Significance We describe a human disease linked to mutations in the linear deubiquitinase (DUB) OTULIN, which functions as a Met1-specific DUB to remove linear polyubiquitin chains that are assembled by the linear ubiquitin assembly complex (LUBAC). OTULIN has a role in regulating Wnt and innate immune signaling complexes. Hydrolysis of Met1-linked ubiquitin chains attenuates inflammatory signals in the NF-κB and ASC-mediated pathways. OTULIN-deficient patients have excessive linear ubiquitination of target proteins, such as NEMO, RIPK1, TNFR1, and ASC, leading to severe inflammation. Cytokine inhibitors have been efficient in suppressing constitutive inflammation in these patients. This study, together with the identification of haploinsufficiency of A20 (HA20), suggests a category of human inflammatory diseases, diseases of dysregulated ubiquitination. Systemic autoinflammatory diseases are caused by mutations in genes that function in innate immunity. Here, we report an autoinflammatory disease caused by loss-of-function mutations in OTULIN (FAM105B), encoding a deubiquitinase with linear linkage specificity. We identified two missense and one frameshift mutations in one Pakistani and two Turkish families with four affected patients. Patients presented with neonatal-onset fever, neutrophilic dermatitis/panniculitis, and failure to thrive, but without obvious primary immunodeficiency. HEK293 cells transfected with mutated OTULIN had decreased enzyme activity relative to cells transfected with WT OTULIN, and showed a substantial defect in the linear deubiquitination of target molecules. Stimulated patients’ fibroblasts and peripheral blood mononuclear cells showed evidence for increased signaling in the canonical NF-κB pathway and accumulated linear ubiquitin aggregates. Levels of proinflammatory cytokines were significantly increased in the supernatants of stimulated primary cells and serum samples. This discovery adds to the emerging spectrum of human diseases caused by defects in the ubiquitin pathway and suggests a role for targeted cytokine therapies.

A patient with hyper-IgD syndrome responding to anti-TNF treatment

The hyperimmunoglobulinemia D periodic fever syndrome (HIDS) is caused by recessive mutations in the mevalonate kinase gene, which encodes an enzyme involved in cholesterol and nonsterol isoprenoid biosynthesis. The pathogenesis and treatment remains unclear. We describe a 6-year-old Turkish girl with severe disease. Her clinical features were accompanied with very high acute-phase reactants including a very high serum amyloid A level. The patient responded well to anti-tumor necrosis factor treatment. Our findings support the use of this anti-cytokine treatment in HIDS.

Confirmation of the ATP6B1 gene as responsible for distal renal tubular acidosis

Abstract.Primary distal renal tubular acidosis (dRTA) type I is a hereditary renal tubular disorder, which is characterized by impaired renal acid secretion resulting in metabolic acidosis. Clinical symptoms are nephrocalcinosis, nephrolithiasis, osteomalacia, and growth retardation. Biochemical alterations consist of hyperchloremic metabolic acidosis, hypokalemia with muscle weakness, hypercalciuria, and inappropriately raised urinary pH. Autosomal dominant and rare forms of recessive dRTA are known to be caused by mutations in the gene for the anion exchanger AE1. In order to identify a gene responsible for recessive dRTA, we performed a total genome scan with 303 polymorphic microsatellite markers in six consanguineous families with recessive dRTA from Turkey. In four of these there was an association with sensorineural deafness. The total genome scan yielded regions of homozygosity by descent in all six families on chromosomes 1, 2, and 10 as positional candidate region. In one of these regions the gene ATP6B1 for the ß1 subunit of the vacuolar H+-ATPase is localized, which has recently been identified as causative for recessive dRTA with sensorineural deafness. Therefore, we conducted mutational analysis in 15 families and identified potential loss-of-function mutations in ATP6B1 in 8. We thus confirmed that defects in this gene are responsible for recessive dRTA with sensorineural deafness.

The significance of IgA class of antineutrophil cytoplasmic antibodies (ANCA) in childhood Henoch–Schönlein purpura

Antineutrophil cytoplasmic antibodies (ANCA) have been identified in a wide variety of vasculitic disorders, but it is controversial whether ANCA are present in the sera of patients with HSP. This prospective study was designed to assess the place of ANCA, particularly their IgA subclass, in HSP. Thirty-five patients (18 boys, 17 girls) aged 9.4±4 (3–16) years with a clinical diagnosis of HSP based on American College of Rheumatology (ACR) criteria were enrolled. Thirteen patients (6 boys, 7 girls) aged 8.3±5.5 (2–21) years with other vasculitides, consisting of classic polyarteritis nodosa (PAN) (n=2); cutaneous polyarteritis nodosa (n=1); acute infantile hemorrhagic edema (n=2); acute urticarial vasculitis (n=2); hypocomplementemic vasculitis (n=1); and unclassified vasculitis (n=5) served as disease controls and 10 healthy children served as normal controls. Twenty-five HSP patients and 7 disease controls were re-evaluated in the resolution phase that was described as 4–6 weeks after all symptoms subsided and all medications were stopped. Blood samples for ANCA and IgA rheumatoid factor (RF) were studied by indirect immunofluorescence (IIF) and ELISA, respectively. IgG ANCA was significantly lower in percentage in HSP patients (2.8%) than in disease controls (40%) (p=0.002). In contrast, IgA ANCA in cytoplasmic pattern was detected in a significantly higher percentage of HSP patients (82.3%) in the acute phase compared to those in the disease controls (38%) (p=0.004). In the resolution phase, IgA ANCA was negative in 88% of the patients (p= 0.001 for acute vs resolution phases). Neither IgG nor IgA ANCA were seen in normal controls. No relationship was found between disease severity of HSP and IgA ANCA. Positive IgA rheumatoid factor was present in only two patients with HSP. In conclusion, our results suggest that IgA ANCA may be useful to confirm the diagnosis of HSP in children.