David V. Milford

Mutation of BSND causes Bartter syndrome with sensorineural deafness and kidney failure

Antenatal Bartter syndrome (aBS) comprises a heterogeneous group of autosomal recessive salt-losing nephropathies. Identification of three genes that code for renal transporters and channels as responsible for aBS has resulted in new insights into renal salt handling, diuretic action and blood-pressure regulation. A gene locus of a fourth variant of aBS called BSND, which in contrast to the other forms is associated with sensorineural deafness (SND) and renal failure, has been mapped to chromosome 1p. We report here the identification by positional cloning, in a region not covered by the human genome sequencing projects, of a new gene, BSND, as the cause of BSND. We examined ten families with BSND and detected seven different mutations in BSND that probably result in loss of function. In accordance with the phenotype, BSND is expressed in the thin limb and the thick ascending limb of the loop of Henle in the kidney and in the dark cells of the inner ear. The gene encodes a hitherto unknown protein with two putative transmembrane α-helices and thus might function as a regulator for ion-transport proteins involved in aBS, or else as a new transporter or channel itself.

Haemolytic uraemic syndromes in the British Isles, 1985-8: association with verocytotoxin producing Escherichia coli. Part 2: Microbiological aspects.

In a three year study of children under 16 years with haemolytic uraemic syndrome faecal samples were examined for the presence of Verocytotoxin producing Escherichia coli (VTEC) using DNA probes and for free neutralisable Verocytotoxin in a Vero cell assay with specific antisera. There was evidence of VTEC infection in 58 of 185 (31%) samples. A total of 53 VTEC was identified from patients with haemolytic uraemic syndrome. Thirty eight VTEC belonged to serotype O157:H7 or O157:H-, 34 produced VT2 only, and four strains produced both VT1 and VT2. The remaining 15 VTEC belonged to nine different O serogroups; three strains produced VT1, 10 produced VT2, and two were positive for VT1 and VT2. Three control groups of patients without haemolytic uraemic syndrome were also examined. There was evidence of VTEC infection in 8%, 6%, and 4% of specimens from individuals with bloody diarrhoea, those with diarrhoea only, and healthy controls respectively. VTEC from the bloody diarrhoeal and diarrhoeal controls were O157:H7 but those from the healty controls could not be O serogrouped. This study confirms the association of VTEC, and particularly strains of O157:H7, with haemolytic uraemic syndrome. Strains producing VT1, VT2, or both toxins were isolated, although over 94% of VTEC produced VT2 alone or together with VT1.

Hypertension in the syndrome of apparent mineralocorticoid excess due to mutation of the 11β-hydroxysteroid dehydrogenase type 2 gene

BACKGROUND 11 beta-hydroxysteroid dehydrogenase (11 beta-HSD) catalyses the interconversion of hormonally active cortisol to inactive cortisone and is vital for dictating specificity for the mineralocorticoid receptor. Thus, in patients with congenital deficiency of 11 beta-HSD (the syndrome of apparent mineralocorticoid excess, AME), cortisol and not aldosterone acts as a mineralocorticoid, resulting in hypertension and hypokalaemia with suppression of the renin-angiotensin-aldosterone axis. Two isoforms of human 11 beta-HSD have been described, but it is the NAD-dependent type 2 isoform (11 beta-HSD2), first characterised in placental tissue, that is expressed in the mineralocorticoid target tissues, kidney and colon. We have analysed the 11 beta-HSD2 gene as a candidate gene in explaining the molecular basis of AME. METHODS By exon-specific PCR-amplification of the 11 beta-HSD2 gene in a consanguineous kindred with AME, we found a point mutation (C1228T) in two affected siblings, and also in placental DNA obtained from a stillbirth pregnancy. FINDINGS The mutation in exon 5 of the 11 beta-HSD2 gene resulted in a premature stop site at codon 374 instead of a normal arginine (R374X), with the deletion of 32 aminoacids from the C-terminus of the 11 beta-HSD2 enzyme protein. Both parents, who are phenotypically normal, are heterozygote for the C1228T mutation in keeping with an autosomal recessive form of inheritance. NAD-dependent 11 beta-HSD activity was severely attenuated in the stillbirth placenta compared with control placental tissue, and no 11 beta-HSD immunostaining was observed in this placenta with antisera derived against a C-terminal 11 beta-HSD2 peptide sequence. INTERPRETATION AME is due to a mutation in the 11 beta-HSD2 gene, and is an example of human hypertension arising from a single gene defect.

The gene mutated in juvenile nephronophthisis type 4 encodes a novel protein that interacts with nephrocystin

Nephronophthisis, the most common genetic cause of chronic renal failure in children, is a progressive tubulo-interstitial kidney disorder that is inherited as an autosomal recessive trait. The disease is characterized by polyuria, growth retardation and deterioration of renal function during childhood or adolescence. The most prominent histological features are modifications of the tubules with thickening of the basement membrane, interstitial fibrosis and, in the advanced stages, medullary cysts. Nephronophthisis can also be associated with conditions affecting extrarenal organs, such as retinitis pigmentosa (Senior–Løken syndrome) and ocular motor apraxia (Cogan syndrome). Three loci are associated with the juvenile, infantile and adolescent forms, on chromosomes 2q13 (NPHP1; refs 5,6), 9q22 (NPHP2; ref. 7) and 3q21 (NPHP3; ref. 8), respectively. NPHP1, the only gene identified so far, encodes nephrocystin, which contains a Src homology 3 (SH3) domain and interacts with intracytoplasmic proteins involved in cell adhesion. Recently, a second locus associated with the juvenile form of the disease, NPHP4, was mapped to chromosome 1p36 (ref. 14). We carried out haplotype analysis of families affected with nephronophthisis that were not linked to the NPHP1, NPHP2 or NPHP3 loci, using markers covering this region. This allowed us to reduce the NPHP4 interval to a one centimorgan interval between D1S2795 and D1S2870, which contains six genes. We identified five different mutations in one of these genes, designated NPHP4, in unrelated individuals with nephronophthisis. The NPHP4 gene encodes a 1,250–amino acid protein of unknown function that we named nephrocystin-4. We demonstrated the interaction of nephrocystin-4 with nephrocystin suggesting that these two proteins participate in a common signaling pathway.

Randomized trial of tacrolimus versus cyclosporin microemulsion in renal transplantation.

Abstract This study was undertaken to compare the efficacy and safety of tacrolimus (Tac) with the microemulsion formulation of cyclosporin (CyA) in children undergoing renal transplantation. A 6-month, randomized, prospective, open, parallel group study with an open extension phase was conducted in 18 centers from nine European countries. In total, 196 pediatric patients (<18 years) were randomly assigned (1:1) to receive either Tac (n=103) or CyA microemulsion (n=93) administered concomitantly with azathioprine and corticosteroids. The primary endpoint was incidence and time to first acute rejection. Baselinecharacteristics were comparable between treatment groups. Tac therapy resulted in a significantly lower incidence of acute re-jection (36.9%) compared with CyA therapy (59.1%) (P=0.003). The incidence of corticosteroid-resistant rejection was also significantly lower in the Tac group compared with the CyA group (7.8% vs. 25.8%, P=0.001). The differences were also significant for biopsy-confirmed acute rejection (16.5% vs. 39.8%, P<0.001). At 1 year, patient survival was similar (96.1% vs. 96.6%), while 10 grafts were lost in the Tac group compared with 17 graft losses in the CyA group (P=0.06). At 1 year, mean glomerular filtration rate (Schwartz estimate) was significantly higher in the Tac group (62±20 ml/min per 1.73 m2, n=84) than in the CyA group (56±21 ml/min per 1.73 m2, n=74, P=0.03). The most frequent adverse events during the first 6 months were hypertension (68.9% vs. 61.3%), hypomagnesemia (34.0% vs. 12.9%, P=0.001), and urinary tract infection (29.1% vs. 33.3%). Statistically significant differences (P<0.05) were observed for diarrhea (13.6% vs. 3.2%), hypertrichosis (0.0% vs. 7.5%), flu syndrome (0.0% vs. 5.4%), and gum hyperplasia (0.0% vs. 5.4%). In previously non-diabetic children, the incidence of long-term (>30 days) insulin use was 3.0% (Tac) and 2.2% (CyA). Post-transplant lymphoproliferative disease was observed in 1 patient in the Tac group and 2 patients in the CyA group. In conclusion, Tac was significantly more effective than CyA microemulsion in preventing acute rejection after renal transplantation in a pediatric population. The overall safety profiles of the two regimens were comparable.

Mineral Metabolism and Vascular Damage in Children on Dialysis

Cardiovascular disease is increasingly recognized as a life-limiting problem in young patients with chronic kidney disease, but there are few studies in children that describe its determinants. We studied the association of intact parathyroid hormone (iPTH) levels and their management on vascular structure and function in 85 children, ages 5-18 years, who had received dialysis for > or =6 months. Compared to controls, dialysis patients had increased carotid intima-media thickness and pulse-wave velocity. All vascular measures positively correlated with serum phosphorus levels, while carotid intima-media thickness and cardiac calcification score also correlated with iPTH levels. Patients with mean time-integrated iPTH levels less than twice the upper limit of normal (n = 41) had vascular measures that were comparable to age-matched controls, but those with iPTH levels greater than twice the upper limit of normal (n = 44) had greater carotid intima-media thickness, stiffer vessels, and increased cardiac calcification than controls. Patients with increased carotid intima-media thickness had stiffer vessels and a greater prevalence of cardiac calcification. There was a strong dose-dependent correlation between vitamin D and all vascular measures, and calcium intake from phosphate binders weakly correlated with carotid intima-media thickness. In conclusion, both iPTH level and dosage of vitamin D are associated with vascular damage and calcification in children on dialysis.

The definition of acute kidney injury and its use in practice.

Acute kidney injury (AKI) is a common syndrome that is independently associated with increased mortality. A standardized definition is important to facilitate clinical care and research. The definition of AKI has evolved rapidly since 2004, with the introduction of the Risk, Injury, Failure, Loss, and End-stage renal disease (RIFLE), AKI Network (AKIN), and Kidney Disease Improving Global Outcomes (KDIGO) classifications. RIFLE was modified for pediatric use (pRIFLE). They were developed using both evidence and consensus. Small rises in serum creatinine are independently associated with increased mortality, and hence are incorporated into the current definition of AKI. The recent definition from the international KDIGO guideline merged RIFLE and AKIN. Systematic review has found that these definitions do not differ significantly in their performance. Health-care staff caring for children or adults should use standard criteria for AKI, such as the pRIFLE or KDIGO definitions, respectively. These efforts to standardize AKI definition are a substantial advance, although areas of uncertainty remain. The new definitions have enabled the use of electronic alerts to warn clinicians of possible AKI. Novel biomarkers may further refine the definition of AKI, but their use will need to produce tangible improvements in outcomes and cost effectiveness. Further developments in AKI definitions should be informed by research into their practical application across health-care providers. This review will discuss the definition of AKI and its use in practice for clinicians and laboratory scientists.

Haemolytic uraemic syndromes in the British Isles 1985-8: association with verocytotoxin producing Escherichia coli. Part 1: Clinical and epidemiological aspects.

A prospective study of the clinical and epidemiological features of the haemolytic uraemic syndromes was conducted over a three year period in the British Isles. Two hundred and ninety eight children were reported. In two thirds of cases stool samples were analysed for the presence of Verocytotoxin producing Escherichia coli (VTEC) and neutralisable Verocytotoxin. A total of 273 (95%) patients had a prodrome of diarrhoea. In these a seasonal variation in the incidence of haemolytic uraemic syndrome was demonstrated, the 1-2 year age range was most often affected, and the peripheral blood neutrophil count correlated positively with an adverse outcome. Patients presenting without diarrhoea showed none of these associations and had a significantly greater morbidity and mortality. Evidence for VTEC infection was found in 58 (33%) of 178 diarrhoea associated cases whose stools were analysed, although VTEC were identified in five of eight (62%) patients whose stools were collected within three days of the onset of diarrhoea. Most isolates produced VT2 either alone, or together with VT1. There was no evidence of VTEC infection in patients without prodromal diarrhoea.

Manifestations and treatment of Schimke immuno-osseous dysplasia: 14 new cases and a review of the literature.

Abstract Schimke immuno-osseous dysplasia (SIOD) is a rare autosomal recessive spondylo-epiphyseal dysplasia. The characteristic features of SIOD include 1) short stature with hyperpigmented macules and an unusual facies, 2) proteinuria with progressive renal failure, 3) lymphopenia with recurrent infections, and 4) cerebral ischaemia. Although 25 patients have been reported with this disorder, the clinical course and phenotype of SIOD are not well characterized. This report summarizes the clinical findings, course and treatment of reported patients and includes 14 additional patients with SIOD. We emphasize the high incidence of cerebral ischaemia and ocular abnormalities, define the high incidence of thyroid dysfunction and blood cytopenia, and confirm the absence of effective and durable medical therapies. Conclusion Schimke immuno-osseous dysplasia is a multi-system autosomal recessive disorder with variable expression that affects the skeletal, renal, immune, vascular, and haematopoietic systems. Medical therapy is limited especially for more severely affected individuals.

Renal histopathology in fatal cases of diarrhoea-associated haemolytic uraemic syndrome

Abstract. Autopsy material was examined from British children dying early in the course of haemolytic uraemic syndrome (HUS). These presented after 1983, the period in which verocytotoxin-producing Escherichia coli (VTEC) infection was confirmed as the leading cause of diarrhoea-associated (D+HUS) in the United Kingdom. Of 18 cases referred for this study, 3 were found on review to have no history of a diarrhoeal prodrome (D-HUS). In the D+ patients, the median duration from onset of diarrhoea to death was 8 days (range 4–42 days). VTEC infection was confirmed in 6 cases. All had neutrophilia at presentation (median 21, range 15–49.8 × 109/l). The 15 cases had uniform pathological features, consisting of glomerular thromboses and congested rather than ischaemic glomeruli. Arteriolar thromboses were common at the hilum of glomeruli and were sometimes also seen proximally, including in interlobular arteries. There were cortical infarcts in 5 cases with extensive thrombosis. Cases were demonstrated to have significantly greater numbers of neutrophils expressed per 100 glomeruli than controls, when counted using immunohistological stains to neutrophil elastase and CD15. This study showed uniformity of the renal changes in D+ HUS and gave further evidence of the importance of neutrophils in the pathogenesis of the disease.