Mutations in ATP6N1B, encoding a new kidney vacuolar proton pump 116-kD subunit, cause recessive distal renal tubular acidosis with preserved hearing.

The multi-subunit H+-ATPase pump is present at particularly high density on the apical (luminal) surface of -intercalated cells of the cortical collecting duct of the distal nephron, where vectorial proton transport is required for urinary acidification. The complete subunit composition of the apical ATPase, however, has not been fully agreed upon. Functional failure of -intercalated cells results in a group of disorders, the distal renal tubular acidoses (dRTA), whose features include metabolic acidosis accompanied by disturbances of potassium balance, urinary calcium solubility, bone physiology and growth. Mutations in the gene encoding the B-subunit of the apical pump (ATP6B1) cause dRTA accompanied by deafness. We previously localized a gene for dRTA with preserved hearing to 7q33-34 (ref. 4). We report here the identification of this gene, ATP6N1B, which encodes an 840 amino acid novel kidney-specific isoform of ATP6N1A, the 116-kD non-catalytic accessory subunit of the proton pump. Northern-blot analysis demonstrated ATP6N1B expression in kidney but not other main organs. Immunofluorescence studies in human kidney cortex revealed that ATP6N1B localizes almost exclusively to the apical surface of -intercalated cells. We screened nine dRTA kindreds with normal audiometry that linked to the ATP6N1B locus, and identified different homozygous mutations in ATP6N1B in eight. These include nonsense, deletion and splice-site changes, all of which will truncate the protein. Our findings identify a new kidney-specific proton pump 116-kD accessory subunit that is highly expressed in proton-secreting cells in the distal nephron, and illustrate its essential role in normal vectorial acid transport into the urine by the kidney.

Mutations in the chloride channel gene, CLCNKB, cause Bartter's syndrome type III.

Analysis of patients with inherited hypokalaemic alkalosis resulting from salt-wasting has proved fertile ground for identification of essential elements of renal salt homeostasis and blood-pressure regulation. We now demonstrate linkage of this phenotype to a segment of chromosome 1 containing the gene encoding a renal chloride channel, CLCNKB. Examination of this gene reveals loss-of-function mutations that impair renal chloride reabsorption in the thick ascending limb of Henle's loop. Mutations in seventeen kindreds have been identified, and they include large deletions and nonsense and missense mutations. Some of the deletions are shown to have arisen by unequal crossing over between CLCNKB and the nearby related gene, CLCNKA. Patients who harbour CLCNKB mutations are characterized by hypokalaemic alkalosis with salt-wasting, low blood pressure, normal magnesium and hyper- or normocalciuria; they define a distinct subset of patients with Bartter's syndrome in whom nephrocalcinosis is absent. These findings demonstrate the critical role of CLCNKB in renal salt reabsorption and blood-pressure homeostasis, and demonstrate the potential role of specific CLCNKB antagonists as diuretic antihypertensive agents.

Mutations in the gene encoding B1 subunit of H+-ATPase cause renal tubular acidosis with sensorineural deafness.

H+-ATPases are ubiquitous in nature; V-ATPases pump protons against an electrochemical gradient, whereas F-ATPases reverse the process, synthesizing ATP. We demonstrate here that mutations in ATP6B1, encoding the B-subunit of the apical proton pump mediating distal nephron acid secretion, cause distal renal tubular acidosis, a condition characterized by impaired renal acid secretion resulting in metabolic acidosis. Patients with ATP6B1 mutations also have sensorineural hearing loss; consistent with this finding, we demonstrate expression of ATP6B1 in cochlea and endolymphatic sac. Our data, together with the known requirement for active proton secretion to maintain proper endolymph pH, implicate ATP6B1 in endolymph pH homeostasis and in normal auditory function. ATP6B1 is the first member of the H+-ATPase gene family in which mutations are shown to cause human disease.

Disease severity in children and adolescents with familial Mediterranean fever: a comparative study to explore environmental effects on a monogenic disease.

BACKGROUND: Worldwide, familial Mediterranean fever (FMF) is the most common autoinflammatory disease. It has been suggested that environmental factors affect the phenotype as some patients do not develop the complication of secondary amyloidosis. OBJECTIVE: To analyse whether disease severity in Turkish children with FMF, living in Turkey and Germany is different. PATIENTS AND METHODS: A total of 55 Turkish children living in Turkey were compared with 45 Turkish children born and raised in Germany. Mean age among the group from Turkey and Germany was 42.2 and 44.29 months, respectively. M694V was the leading mutation in both groups. The severity scores were compared with two scoring systems, modified according to published paediatric data for dosage. RESULTS: There was no significant difference between the mean C-reactive protein and erythrocyte sedimentation rate levels of the two groups. According to the modified Sheba Center score, 78.2% of patients from the group living in Turkey had a severe course compared with 34.1% from the group living in Germany. The modified score of Pras et al also showed more severe disease in the patients from Turkey. The difference between the two groups for both scoring systems were significant (both p<0.05). CONCLUSIONS: We believe the modified scores that we introduce can be widely used for children. Our results suggest that the environment affects the phenotype of a monogenic disease of the innate inflammatory pathway.

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.

Henoch-Schönlein nephritis: a nationwide study.

BACKGROUND/AIM: The aim of this retrospective study was to evaluate the presentation, clinical and pathological manifestations and outcome of the Henoch-Schönlein purpura (HSP) nephritis in children. METHODS: Clinical and laboratory data of 443 children with HSP nephritis aged between 3 and 16 years from 16 pediatric nephrology reference centers were analyzed retrospectively. The biopsy findings were graded according to the classification developed by the International Study of Kidney Disease in Children (ISKDC). RESULTS: Renal biopsy was performed in 179 of the patients with HSP nephritis. The most common presenting clinical finding in patients who were biopsied was nephrotic range proteinuria (25%) which was followed by nephritic-nephrotic syndrome (23.5%). The biopsy findings according to the ISKDC were as follows: class I: 8.3%; II: 44.1%; III: 36.3%; IV: 6.7%; V: 3.3%; VI: 1.1%. All of the patients who developed end-stage renal disease had nephritic-nephrotic syndrome at presentation. Of 443 patients, 87.2% had a favorable outcome and 12.8% had an unfavorable outcome. The overall percentage of children who developed end-stage renal disease at follow-up was 1.1%. Logistic regression analysis did not show any association of initial symptoms and histology with outcome. CONCLUSION: In the presented cohort, the presence of crescents in the first biopsy or presenting clinical findings did not seem to predict the outcome of HSP nephritis in children. We conclude that children with HSP nephritis even with isolated microscopic hematuria and/or mild proteinuria should be followed closely.

The analysis of interleukin-1 receptor antagonist and interleukin-1beta gene polymorphisms in Turkish FMF patients: do they predispose to secondary amyloidosis?

OBJECTIVE: Amyloid development in familial Mediterranean fever (FMF) patients is associated with acute phase response and the acute phase reactant serum amyloid A which is induced by IL-1Beta. Its concentration can increase to more than 1000 fold during inflammation. In view of the inflammatory nature of FMF disease we have investigated whether IL-1Beta and IL-1 receptor antagonist gene polymorphisms may be involved in amyloid development in FMF patients. METHODS: Ninety-nine FMF patients without amyloidosis; 54 FMF patients with amyloidosis and 60 healthy controls samples were genotyped for IL-1Beta-511 (C/T) and IL-1Beta+3953 (C/T) polymorphisms using PCR-RFLP and for IL-1Ra VNTR polymorphism using PCR. RESULTS: The allele and genotype frequencies of IL-1Beta-511 (C/T), IL-1Beta+3953 (C/T) and IL-1Ra VNTR polymorphisms in FMF patients with and without amyloidosis were all compared with those in controls. There were no significant differences between FMF patients with and without amyloidosis and healthy control samples for these polymorphisms (all P-values are >0.05). These polymorphisms were not associated with M694V mutation in FMF patients with and without amyloidosis. CONCLUSION: IL-1Beta-511 (C/T), IL-1Beta+3953 (C/T) and IL-1Ra VNTR polymorphisms are not associated with the development of amyloid in FMF patients.

Preoperative evaluation of hilar vessel anatomy with 3-D computerized tomography in living kidney donors.

OBJECTIVES: Digital subtract angiography is the gold standard for anatomic assessment of renal vasculature for living renal donors. However, multidetector-row computerized tomography (MDCT) is less invasive than digital subtract angiography and provides information of kidney stones and other intra-abdominal organs. In this study, preoperative MDCT angiography results were compared with the peroperative findings to evaluate the accuracy of MDCT for the evaluation of renal anatomy. METHODS: From December 2002 to May 2007, all 60 consecutive living kidney donors were evaluated with MDCT angiography preoperatively. We reported the number and origin of renal arteries, presence of early branching arteries, and any intrinsic renal artery disease. Renal venous anatomy was evaluated for the presence of accessory, retroaortic, and circumaortic veins using venous phase axial images. The calyces and ureters were assessed with delayed topograms. The results of the MDCT angiography were compared with the peroperative findings. RESULTS: A total of 67 renal arteries were seen peroperatively in 60 renal units. Preoperative MDCT angiography detected 64 of them. The two arteries not detected by MDCT had diameters less than 3 mm. Anatomic variations were present in nine veins, five of which were detected by CT angiography. Sensitivity of MDCT angiography for arteries and veins was 95% and 93%, respectively. Positive predictive values were 100% for both arteries and veins. CONCLUSION: MDCT angiography offers a less invasive, rapid, and accurate preoperative investigation modality for vascular anatomy in living kidney donors. It also provides sufficient information about extrarenal anatomy important for donor surgery.

Renal transplantation in children with lower urinary tract dysfunction of different origin: a single-center experience.

INTRODUCTION: Renal transplantation in patients with lower urinary tract dysfunction (LUTD) of various origins is a challenging issue in the field of pediatric transplantation. We report our single-center experience to evaluate patient and graft survivals as well as the risks of the surgery and immunosuppressive therapy. PATIENTS AND METHODS: Among 70 pediatric transplant patients, 11 displayed severe LUTD. Videourodynamic tests were performed on all patients preoperatively as well as postoperatively if required. The cause of urologic disorders were neurogenic bladder (n = 5) and urethral valves (n = 6). Clean intermittent catheterization (CIC) was needed in six patients to empty the bladder. To achieve a low-pressure reservoir with adequate capacity pretransplantation augmentation ileocystoplasty was created in four patients and gastrocystoplasty in one patient. Three of the patients received kidneys from cadaveric and eight from living donors. All patients were treated with calcineurin-based immunosuppressive therapy. RESULTS: The mean age at transplantation was 15 +/- 4.7 years. The median follow-up after transplantation was 36 months (6 to 62 months). At their last visit the median creatinine level was 0.95 mg/dL (0.8 to 2.4 mg/dL). Three patients had recurrent symptomatic urinary tract infections who had augmented bladder on CIC. One patient with ileocystoplasty who developed urinary leak and ureteral stricture in the early postoperative period was treated by an antegrade J stent. CONCLUSION: Severe LUTD carried high risks for the grafted kidney. However, our data suggested that renal transplantation is a safe and effective treatment modality, if the underlying urologic diseases properly managed during the transplantation course. Since surgery and follow-up is more complicated, patient compliance and experience of transplantation team have significant impacts on outcomes.

Outcome of primary glomerular disease in pediatric renal transplantation: a single-center experience.

INTRODUCTION: The recurrence of primary disease in transplantation is a well-known problem. We report our single-center experience to assess the frequency of the recurrence of primary glomerulonephritis in children after renal transplantation. PATIENTS AND METHODS: Medical reports of 14 children with primary glomerular disease were evaluated. Among the 14 grafts were 10 from living related and four from cadaveric donors. Ten were diagnosed as focal segmental glomerulosclerosis (FSGS), two membranoproliferative glomerulonephritis (MPGN), and two polyarteritis nodosa (PAN). The original diagnosis was biopsy-proven in every case. All patients were treated with calcineurin-based immunosuppressive therapy. RESULTS: The mean age was 15.5 +/- 5.4 years. The median transplantation duration was 47 months; however, one of the FSGS patient had hyperacute rejection. Five years later she received a second graft with a serum creatinine of 0.7 mg/dL at 7 years after transplantation. Posttransplant recurrence of FSGS was confirmed in two patients (20%), who were treated with plasmapheresis with no improvement of proteinuria, two FSGS patients had thromboses after transplantation. One had a cardiac thrombosis with heterozygote MTHFR mutation and one, a renal artery thrombosis and loss of graft with prothrombin 20210A mutation. They all have functioning grafts except these two. We did not observe recurrence of PAN or MPGN in patients. CONCLUSION: Although the number of patients is quite small, our recurrence rate was compatible with the previous reports. Additionally, we strongly recommend evaluation of all risk factors for thrombosis and give appropriate anticoagulation.

Triple immunosuppression with tacrolimus in pediatric renal transplantation: single-center experience.

AIM: In this single-center cohort, we retrospectively analyzed the efficacy and safety of tacrolimus in pediatric renal transplantation. METHODS: We examined the medical records of 22 consecutive renal transplantation recipients (12 boys, 10 girls) receiving tacrolimus, to evaluate occurrence of acute rejection (AR) episodes, glomerular filtration rates (GFR), and side effects. RESULTS: The mean recipient age was 15.07 +/- 3.96 years. Seven grafts came from cadaveric, and 15 from living related donors. The patients were placed on immunosuppression with prednisolone and tacrolimus plus azathioprine (n = 8) or mycophenolate mofetil (MMF) (n = 12) or enteric-coated mycophenolate sodium (n = 2). Eighteen patients received basiliximab on days 0 and 4. There were three AR episodes at 5, 9, and 12 months. Mean GFR at the end of 1 and 2 years were 97.1 +/- 24.0 mL/min/1.73 m(2) and 116.9 +/- 42.2 mL/min/1.73 m(2), respectively. There was no graft loss. Hypertension, hyperlipidemia, and hyperglycemia were present in 14 (63.6%), 3 (13.6%), and 3 (13.6%) patients, respectively, without gingival hyperplasia, tremor, or hypertrichosis. Supraventricular tachycardia was noticed in five patients (22.7%), three of whom needed antiarrhythmic drugs (13.6%). CONCLUSION: Our single-center experience with tacrolimus, steroid plus azathioprine or MMF or enteric-coated mycophenolate sodium regimen in pediatric kidney recipients showed a low rate of AR with excellent graft survival and function at 1 and 2 year posttransplantation. The increased rate of supraventricular tachycardia in this regimen had not been previously reported; this association merits further studies.

Interferon-gamma assays for the diagnosis of tuberculosis infection before using tumour necrosis factor-alpha blockers.

OBJECTIVES: Patients who receive tumour necrosis factor-alpha (TNF-alpha) blockers are mostly immunosuppressed. A study was performed to investigate whether an interferon-gamma (IFN-gamma) assay could represent an alternative approach to the tuberculin skin test (TST) for the diagnosis of latent tuberculosis infection (LTBI) in these patients. DESIGN: We prospectively enrolled 106 individuals into the study in two groups. Group 1 consisted of 38 healthy individuals and Group 2 included 68 patients with chronic inflammatory diseases evaluated for LTBI before the use of TNF-alpha blockers. RESULTS: Of all participants, nine had indeterminate IFN-gamma test results. Agreement between the two tests was poor in both groups (kappa values respectively -0.54 and 0.18). In a total of 97 subjects, 10 (10.3%) were positive by the IFN-gamma test and 49 (50.5%) by TST. CONCLUSION: We found poor agreement between TST and the IFN-gamma test in our study. Our limited preliminary data should be accepted as a basis for designing future studies that will be helpful for physicians to decide whether the IFN-gamma test is more sensitive than the TST test in detecting LTBI before the use of TNF-alpha blockers.

Are carriers for MEFV mutations "healthy"?

OBJECTIVE: We aimed to compare whether carriers for the MEFV mutations display an increase or decrease in certain features. We compared the frequency of a number of inflammatory symptoms and diseases in carriers and a control population. METHODS: A questionnaire was designed to be applied to parents of children with FMF and a control group of parents. Clinical features and some diseases including the frequency of febrile episodes, abdominal pain, arthralgia, prophylaxis with penicillin, acute rheumatic fever, rheumatoid arthritis, vasculitis, spondyloarthropathy, urinary tract infection, asthma, allergy, irritable bowel disease, appendectomy and tonsillectomy were inquired. 676 parents of 440 children with FMF were surveyed in this study. Controls (n: 774) were selected as parents of healthy children. RESULTS: The presence of febrile episodes more than four per year, arthralgia, past diagnosis for acute rheumatic fever, rheumatoid arthritis and prophylaxis of penicillin, acute rheumatic fever, and rheumatoid arthritis were significantly higher in asymptomatic parents for the MEFV mutations compared to controls. The frequency of allergy was found to be significantly lower in the asymptomatic parents as compared to controls. There was no significant difference at the frequency of urinary tract infection and tonsillectomy between the parents of the patents and controls. CONCLUSIONS: We suggest that one MEFV mutation may indeed be conferring a heightened inflammation as suggested by the increased frequency in inflammatory symptoms. The carrier status for MEFV mutations seem to be unique, in that they cause an alteration in the state of "health".

Semen variables and hormone profiles after kidney transplantation during adolescence.

Our aim was to investigate the semen variables and hormone profiles among transplant patients who received kidneys during adolescence. Seven postpubertal transplant patients who underwent successful renal transplantation during adolescence (13-19 years; 3 were preemptive) were enrolled in our clinical follow-up. Serum levels of prolactin, luteinizing hormone (LH), follicle-stimulating hormone (FSH), and testosterone were checked together with the semen analysis. The ages of the patients ranged from 18 to 25 years (median, 22 years). The median age was 15 years (range, 12-18 years) at initial presentation. The median time between initial diagnosis and transplantation was 12 months (range, 2-60 months). The median follow-up after transplantation was 51 months (range, 23-134 months). Three of the seven patients had unilateral low testicular volume. The renal function tests were within normal limits, as well as serum levels of prolactin, FSH, LH, and testosterone. Sperm counts ranged from 0.2 to 55 million/mL (median, 1.7 million/mL). Only 1 patient (14.2%) had normal sperm parameters. Oligoteratozoospermia (low sperm count and defects in morphology) was observed in 1/7 (14.2%), asthenoteratozoospermia (low levels of motility and defects in morphology) in 1/7 (14.2%), and all parameters were abnormal in 4/7 (57.1%) cases. Our data suggest that in contrast to adult patients, semen variables are severely affected and spermatogenesis does not improve after renal transplantation when the patient was subjected to uremia before or during adolescence, the crucial period for spermatogenesis.

How does the presence of urologic problems change the outcome of kidney transplantation in the pediatric age group.

PURPOSE: We retrospectively reviewed the impact of functional and anatomic urologic disorders on kidney transplantation outcomes in terms of the surgical and long-term results of pediatric renal transplantation. MATERIALS AND METHODS: Of the 55 kidney transplantations in the pediatric age group, end-stage renal disease (ESRD) was secondary to genitourinary disorders in 23 patients (42%). The urologic abnormalities were vesicoureteral reflux in 13 patients (59%), neurogenic bladder in 4 patients (18%), posterior urethral valves in 3 patients (14%), renal stone disease in 4 patients (18%), bilateral ureterovesical junction obstruction in 3 patients (14%), and unilateral renal agenesis with concomitant contralateral ureteropelvic junction obstruction in 1 patient (4%). RESULTS: Of the 23 patients with urologic problems, 19 (83%) had functioning grafts with a mean follow-up of 49 months (range, 7-120 months). In the other 32 patients, 26 (81%) had functioning grafts with a mean follow-up of 43 months (range, 1-144 months). The graft survival, mean serum creatinine, and urinary tract infection rates of the patients did not differ between the two groups. CONCLUSIONS: The presence of functional urologic disorders as the cause of ESRD did not seem to change the outcome of renal transplantation in terms of graft survival when compared with patients without any urologic disorders. Urinary tract infections seem to be a little more common and yet clinically not significant in those patients. Reflux does not always need to be corrected before transplantation, unless it is causing symptoms or infection.

Renal transplantation in children with augmentation enterocystoplasty.

INTRODUCTION: We report our experience with renal transplantation in patients with severe bladder dysfunction who underwent prior augmentation cystoplasty. PATIENTS AND METHODS: Among 58 pediatric patients, three underwent bladder augmentation prior to renal transplantation. The patients' ages at transplantation were 10, 13, and 17. The etiologies of bladder dysfunction were posterior urethral valves in two patients and contracted bladder in one patient. Vesicoureteral reflux was concomitantly present in three patients. Pretransplant ileocystoplasty was created in two patients and gastrocystoplasty in one patient. All patients received kidneys from cadaveric donors and were treated with calcineurin-based immunosuppressive therapy. RESULTS: The patients had normal renal function without hydronephrosis of the transplanted kidney at 13, 22, 49 months follow-up. No patients had morbidity due to technical complications. All the patients were continent. Two of three patients required clean intermittent catheterization from a Mitrofanoff conduit, while one patient spontaneously voids without significant residual urine. Urinary tract infections observed in two patients were successfully treated without any permanent deterioration in graft kidney function. CONCLUSIONS: Our data suggest that augmentation cystoplasty is a safe and effective option to treat patients with end-stage renal disease undergoing kidney transplantation. Experience of the transplantation team with a qualified pediatric urologist is essential due to the potentially high risk of surgical complications during the long term management of these patients.

A phenocopy of CAII deficiency: a novel genetic explanation for inherited infantile osteopetrosis with distal renal tubular acidosis.

The rare bone thickening disease osteopetrosis occurs in various forms, one of which is accompanied by renal tubular acidosis (RTA), and is known as Guibaud-Vainsel syndrome or marble brain disease. Clinical manifestations of this autosomal recessive syndrome comprise increased bone density, growth failure, intracerebral calcification, facial dysmorphism, mental retardation, and conductive hearing impairment. The most common cause is carbonic anhydrase II (CAII) deficiency. Several different loss of function mutations in CA2, the gene encoding CAII, have been described. To date, there have been no exceptions to the finding of CAII deficiency in patients with coexistent osteopetrosis and RTA. Most often, the RTA is of mixed proximal and distal type, but kindreds are reported in which either distal or proximal RTA predominates. We report the molecular genetic investigation of two consanguineous kindreds where osteopetrosis and distal RTA (dRTA) were both manifest. One kindred harbours a novel homozygous frameshift alteration in CA2. In the other, CAII levels were normal despite a similar clinical picture, and we excluded defects in CA2. In this kindred, two separate recessive disorders are penetrant, each affecting a different, tissue specific subunit of the vacuolar proton pump (H(+)-ATPase), providing a highly unusual, novel genetic explanation for the coexistence of osteopetrosis and dRTA. The osteopetrosis is the result of a homozygous deletion in TCIRG1, which encodes an osteoclast specific isoform of subunit a of the H(+)-ATPase, while the dRTA is associated with a homozygous mutation in ATP6V1B1, encoding the kidney specific B1 subunit of H(+)-ATPase. This kindred is exceptional firstly because the coinheritance of two rare recessive disorders has created a phenocopy of CAII deficiency, and secondly because these disorders affect two different subunits of the H(+)-ATPase that have opposite effects on bone density, but which have only recently been determined to possess tissue specific isoforms.

Novel ATP6V1B1 and ATP6V0A4 mutations in autosomal recessive distal renal tubular acidosis with new evidence for hearing loss.

Autosomal recessive distal renal tubular acidosis (rdRTA) is characterised by severe hyperchloraemic metabolic acidosis in childhood, hypokalaemia, decreased urinary calcium solubility, and impaired bone physiology and growth. Two types of rdRTA have been differentiated by the presence or absence of sensorineural hearing loss, but appear otherwise clinically similar. Recently, we identified mutations in genes encoding two different subunits of the renal alpha-intercalated cell's apical H(+)-ATPase that cause rdRTA. Defects in the B1 subunit gene ATP6V1B1, and the a4 subunit gene ATP6V0A4, cause rdRTA with deafness and with preserved hearing, respectively. We have investigated 26 new rdRTA kindreds, of which 23 are consanguineous. Linkage analysis of seven novel SNPs and five polymorphic markers in, and tightly linked to, ATP6V1B1 and ATP6V0A4 suggested that four families do not link to either locus, providing strong evidence for additional genetic heterogeneity. In ATP6V1B1, one novel and five previously reported mutations were found in 10 kindreds. In 12 ATP6V0A4 kindreds, seven of 10 mutations were novel. A further nine novel ATP6V0A4 mutations were found in "sporadic" cases. The previously reported association between ATP6V1B1 defects and severe hearing loss in childhood was maintained. However, several patients with ATP6V0A4 mutations have developed hearing loss, usually in young adulthood. We show here that ATP6V0A4 is expressed within the human inner ear. These findings provide further evidence for genetic heterogeneity in rdRTA, extend the spectrum of disease causing mutations in ATP6V1B1 and ATP6V0A4, and show ATP6V0A4 expression within the cochlea for the first time.

MEFV mutations in Behçet's disease.

Familial Mediterranean fever (FMF) and Behçet's disease (BD), both inflammatory diseases, are highly prevalent in the Middle Eastern and Mediterranean populations. FMF is a Mendelian autosomic recessive disease linked to MEFV, a gene of unknown function. BD in contrast is a polyfactorial disease associated with the major histocompatibility complex. Because FMF and BD have epidemiological similarities, we asked whether the FMF gene was implicated in BD. We screened for the common MEFV mutations a cohort of 114 chromosomes from definite BD patients [meeting the criteria of the International study group] and probable cases [meeting at least two of these criteria]. We screened in parallel an ethnically matched cohort of FMF and control chromosomes. The M694V, V726A and E148Q mutations tended to be more frequent in definite BD (2.6%, 2.6%, and 5.2%, respectively) than in controls (0%, 0%, and 2.2%). The P706 polymorphism was found in 10.5% of the probable BD chromosomes, but in only 1.6% of the controls (p=0.01). Because some MEFV mutations were more frequent in BD than in controls, we suggest that they may act as additional susceptibility factors in BD.

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%).