ORAI1 channel gating and selectivity is differentially altered by natural mutations in the first or third transmembrane domain

KEY POINTS

Gain-of-function mutations in the highly selective Ca²⁺ channel ORAI1 cause tubular aggregate myopathy (TAM) characterized by muscular pain, weakness and cramping. TAM-associated mutations in ORAI1 first and third transmembrane domain facilitate channel opening by STIM1, causing constitutive Ca²⁺ influx and increasing the currents evoked by Ca²⁺ store depletion. Mutation V107M additionally decreases the channel selectivity for Ca²⁺ ions and its inhibition by acidic pH, while mutation T184M does not alter the channel sensitivity to pH or to reactive oxygen species. The ORAI blocker GSK-7975A prevents the constitutive activity of TAM-associated channels and might be used in therapy for patients suffering from TAM.

ABSTRACT

Skeletal muscle differentiation relies on store-operated Ca²⁺ entry (SOCE) mediated by STIM proteins linking the depletion of endoplasmic/sarcoplasmic reticulum Ca²⁺ stores to the activation of membrane Ca²⁺ -permeable ORAI channels. Gain-of-function mutations in STIM1 or ORAI1 isoforms cause tubular aggregate myopathy (TAM), a skeletal muscle disorder with muscular pain, weakness and cramping. Here, we characterize two overactive ORAI1 mutants from patients with TAM: V107M and T184M, located in the first and third transmembrane domain of the channel. When ectopically expressed in HEK-293T cells or human primary myoblasts, the mutated channels increased basal and store-operated Ca²⁺ entry. The constitutive activity of V107M, L138F, T184M and P245L mutants was prevented by low concentrations of GSK-7975A while the G98S mutant was resistant to inhibition. Electrophysiological recordings confirmed ORAI1-V107M constitutive activity and revealed larger STIM1-gated V107M- and T184M-mediated currents with conserved fast and slow Ca²⁺ -dependent inactivation. Mutation V107M altered the channel selectivity for Ca²⁺ ions and conferred resistance to acidic inhibition. Ca²⁺ imaging and molecular dynamics simulations showed a preserved sensitivity of T184M to the negative regulation by reactive oxygen species. Both mutants were able to mediate SOCE in Stim1^-/- /Stim2^-/- mouse embryonic fibroblasts expressing the binding-deficient STIM1-F394H mutant, indicating a higher sensitivity for STIM1-mediated gating, with ORAI1-T184M gain-of-function being strictly dependent on STIM1. These findings provide new insights into the permeation and regulatory properties of ORAI1 mutants that might translate into therapies against diseases with gain-of-function mutations in ORAI1.

The action of 1,25 (OH)2D3 on turnover kinetic, remodelling surfaces and structure of trabecular bone in chronic renal failure

Fibroosteoclasia as well as osteoidosis are reduced by 1,25(OH)2D3 treatment if secondary hyperparathyroidism preexists. Fibrosteoclasia completely disappeared after 6 months therapy in some cases. 1,25(OH)2D3 has no or only a very slight effect on the disturbed mineralization in type II of renal bone disorder (osteoidosis only, no signs of secondary hyperparathyroidism). The appositional rate of the osteoblasts increases under 1,25(OH)2D3 treatment if serum PTH values are raised. 1,25(OH)2D3 seemed to have, in the chosen dosage of this study, a self-limiting effect by reducing the bone-forming cells, i.e. the osteoblasts. This state already represents an overtreatment of the underlying bone disease.

Fetale Nephro-/Uropathien: Retrospektive Analyse von 124 Fällen, erfasst im Zeitraum von 1996 bis 2002

BACKGROUND

The embryological development of the kidneys and the urinary tract follows a complex choreography. Disorders are quite common. The incidence of disorders amounts to 0.3 - 0.8 % of live-born infants. In addition, several chromosomal anomalies are combined with renal malformations. The poor prognosis of some of these diseases is reflected in a perinatal mortality of 6.3 %.

PATIENTS AND METHODS

Retrospectively 124 cases with fetal nephro-/uropathy detected by prenatal ultrasonography between 1996 and 2002 were analyzed. Features of hypo-dysplastic kidneys (uni- or bilateral) were seen in 21 cases. Multicystic kidney disease (uni- or bilateral) existed in 40 fetuses. In some cases of multicystic or dysplastic kidney diseases, extrarenal malformations were combined. 21 fetuses suffered from autosomal recessive polycystic kidney disease. 18 male unborns showed the typical picture of intravesical obstruction due to posterior uretheral valves. The prune belly syndrome was seen 4 times. Hydronephrotic kidneys with more than 5 mm pelvic dilatation were detected in 13 cases. Renal agenesis led to a lethal outcome perinatally in 5 cases. One child died of bilateral thrombosis of renal artery and venous system.

RESULTS

The high incidence of diseases with a poor prognosis accounts for the high mortality of 50.8 % (intrauterine or postnatal death, induced abortion). Such a fatal outcome was observed in autosomal recessive polycystic kidney disease, bilateral multicystic dysplastic kidney disease, bilateral renal dysplasia combined with severe extrarenal malformations, intravesical obstruction, renal agenesis and bilateral thrombosis of the renal vessels. Only 60 children survived. Of these 26 needed urological surgery. 15 suffered from progressive renal insufficiency. During a follow-up of 8 - 58 months only 44 exhibited a normal renal function.

CONCLUSIONS

Such complex renal and urological diseases in the fetus require an interdisciplinary management of the pregnancy.

Unilateral multicystic dysplastic kidney: experience in children

OBJECTIVES

To report a retrospective study of unilateral multicystic dysplastic kidneys (MCDK) in children, assessing the contralateral kidneys and urinary tract, the functional consequences, and the urological and nephrological management and outcome, as unilateral MCDK is the most common cause of renal cystic disease in children, and malformations of the contralateral urinary tract and kidney (pelvi-ureteric obstruction, megaureter, reflux, renal dysplasia) have been reported.

PATIENTS AND METHODS

The study included 97 patients (60 boys, 37 girls) with MCDK seen between 1985 and 1998; 82 were diagnosed in utero by ultrasonography (US). After birth, the diagnosis was verified by US, renal scanning (in 93) or intravenous urography (in four), and 89 (92%) had voiding cysto-urethrography (VCUG). Of the 97 children, 87 (90% had a mean (range) follow-up of 44.3 (15-115) months.

RESULTS

The MCDK was removed in 17 children; the follow-up of 75 children (five lost to follow-up) showed total involution of the MCDK in 25%, shrinkage in 60% and a stable size in 15%. None had any sign of malignancy. The contralateral kidney showed anomalies in 19 of 97 children (20%); 12 had a dilated renal pelvis (two with megaureter), six had a high echogenicity of the contralateral kidney (one had reflux, and two also pelvic dilatation). In only four of the 89 children was reflux found by VCUG; 16 of the 19 anomalies were detected by US. Five children needed surgery on the contralateral urinary tract (three a pyeloplasty, and one each a pyeloplasty plus ureteroneocystostomy, and an antireflux procedure). Of the contralateral kidneys 43% showed compensatory hypertrophy. There was mild renal insufficiency in three children; renal function seemed to be slightly impaired in many. Five infants had hypertension (four with spontaneous resolution) caused by renal scarring after pyelonephritis or inborn dysplasia of the contralateral kidney. There were symptomatic urinary tract infections in seven children.

CONCLUSION

US can be used safely to diagnose unilateral MCDKs and malformations of the contralateral urinary tract and kidney. In cases where US of the dysplastic kidney remains uncertain renal scintigraphy is necessary to detect the lack of renal function. The low rate of reflux makes routine VCUG unnecessary if the contralateral upper urinary tract and kidney appear to be normal on US. Nephrectomy of the dysplastic kidney in typical cases is also unnecessary. A long-term nephro-urological follow-up of children with MCDK is recommended.

Familial hypomagnesemia-hypercalciuria in 2 siblings

Familial hypomagnesemia-hypercalciuria with nephrocalcinosis and renal insufficiency in childhood is a rarely described disease. Two siblings of consanguineous Tunesian parents (first cousins), a 2-year-old boy and a 4-year-old girl presented with renal insufficiency and severe bilateral nephrocalcinosis. Both were found to have decreased serum and intracellular magnesium concentrations, increased urinary excretion of magnesium and calcium, mild glomerular and severe tubular proteinuria and low citrate excretion in urine. Pathological biochemical findings and the severity of nephrocalcinosis of the boy compared to findings of the sister were strongly marked, Histology of the boy's kidney showed severe medullary nephrocalcinosis, tubular atrophy, focal lymphoplasmacellulary infiltration, focal cortical fibrosis, immature glomerula, segmental and global glomerulosclerosis. Subsequent mutation analysis revealed a homozygous frameshift mutation in the gene paracellin-1 in both affected individuals. Therapy consisted of sodium bicarbonate, cholecalciferol, calcitriol, hydrochlorothiazide, citrate salts and oral magnesium administration. Hypercalciuria decreased in both children by therapy with thiazide diuretics, but hypomagnesemia was unresponsive to magnesium administration. After a 32-month follow-up the boy commenced hemodialysis at the age of 5 years, whereas his sister showed no decline in renal function.

Extracorporeal shock wave lithotripsy in children. Efficacy, complications and long-term follow-up

OBJECTIVES

Extracorporeal shock wave lithotripsy (ESWL) is effective and safe for the treatment of upper urinary tract calculi in adults. Some speculations concerning possible damages from ESWL on the growing kidney have been raised.

METHODS

From January 1990 to December 1998, 64 children (30 girls and 34 boys; 8 months to 15 years old, mean 5.6 years) with a total of 83 stones of the upper urinary tract were treated by ESWL (Lithostar). Preoperative evaluation included history, physical examination, routine blood tests, urinalysis, urine culture, intravenous urography and optional renal scintigraphy. The impulse rate per treatment varied from 750 to 4,000 (mean 2,996). After acute treatment, routine follow-up included renal ultrasound, blood pressure controls, laboratory tests and eventually plain film X-ray.

RESULTS

Successful fragmentation of the stones was achieved in all patients. In 54% the patients were free of stones treated at the time of discharge. At 3 months after treatment radiographic studies showed no residual fragments in 80% of the treated children. 83% of the treated stones were cleared entirely. The remaining fragments were clinically insignificant. An average of 2.5 ESWL treatments per child in general anesthesia were required. Stone analysis showed 20 calcium oxalate, 38 calcium phosphate, 12 struvite, 2 uric acid and 9 cystine calculi. Ureteral stents were placed in 43%. No significant urinary infection was seen under antibiotic prophylaxis. Only 3 children showed a recurrence (1 x cystinuria with low compliance and 2 x struvite). There was no case of renal scarring. No change in renal function or blood pressure was found compared to the preoperative values. Hematuria and proteinuria disappeared in all children who were free of stones. Renal ultrasound revealed no growth difference between treated and untreated renal units.

CONCLUSIONS

In childhood, ESWL is an efficacious and safe treatment of stones of the upper urinary tract. The long-term follow-up after ESWL with a second-generation lithotriptor did not show any signs of damage to the growing kidney. Sometimes repeated ESWL treatments are justified by the low rate of complications.

Renal Fanconi syndrome: first sign of partial respiratory chain complex IV deficiency

A 2-year-old boy who developed hypophosphatemic rickets without signs of muscular weakness or neurological disturbances is presented. Biochemical findings included hypophosphatemia, metabolic acidosis, hypouricemia, hyperphosphaturia, severe glucosuria, generalized hyperaminoaciduria, hypercalciuria, proteinuria with elevated excretion of IgG, transferrin, albumin and high levels of alpha-1-microglobulin. Urine concentration capacity and creatinine clearance were normal. Lactaturia without elevated levels of plasma lactate and a high urinary excretion of beta-hydroxybutyrate were suggestive for mitochondriopathy. Partial deficiency of cytochrome c oxidase (complex IV of the respiratory chain) was found in skeletal muscle. A renal biopsy specimen demonstrated enlarged mitochondria with abnormal arborization and disorientation of the cristae in the proximal tubular cells. Reduced activity of mitochondrial cytochrome c oxidase in tubular cells could be demonstrated by ultracytochemistry. In conclusion, rickets due to the renal Fanconi syndrome can be the first clinical sign of mitochondrial cytopathies without extra-renal symptoms. Elevated excretion of lactate and ketone bodies in urine may serve as a diagnostic marker.

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

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.

[Retinitis pigmentosa, terminal renal insufficiency and Caroli syndrome: new associations with Opitz trigonocephaly syndrome]

We report on a new patient with Opitz trigonocephaly syndrome. In addition to the findings typical of this mental retardation syndrome, the present patient has retinitis pigmentosa, Caroli's syndrome and renal failure, which is undergoing hemodialysis. This association is never observed before in patients with Opitz trigonocephaly syndrome. This case demonstrate, that with increased survival of patients with mental retardation syndromes, the phenotypes possible are modified.

Spectrum of early onset nephrotic syndrome associated with WT1 missense mutations

We investigated 17 children with nephrotic syndrome (NS) of early onset (14 aged < 1 year) and rapid progression to end-stage renal disease for the presence of mutations in the Wilms' tumor suppressor gene WT1 on chromosome 11. In eight children (7 genotypic males) an association with Wilms' tumor and/or ambiguous genitalia (Denys-Drash syndrome) was observed. In these eight and two additional female patients with NS only constitutional missense mutations in the WT1 gene were detected; four children presented the so-called hot spot mutation in exon 9 (R394N) and six had different mutations in exons 8 and 9 (4 not previously described). Renal biopsy showed diffuse mesangial sclerosis in eight and focal segmental sclerosis in two cases. End-stage renal disease was reached either concomitantly or within four months after onset of NS in seven of ten patients. A unilateral Wilms' tumor was found before or concomitant with NS in four children (3 males, 1 female). From the seven genotypic males with WT1 mutations, five presented ambiguous genitalia and two a female phenotype. No mutation of the WT1 gene was found in seven other children with isolated congenital or infantile NS with or without DMS who appeared to have a slower progression than the first group. It is proposed that patients with early onset, rapidly progressive NS and diffuse mesangial or focal segmental sclerosis should be tested for WT1 mutations to identify those at risk for developing Wilms' tumor.

The addition of aminoacids and phosphate to hemodiafiltration solutions in newborns with hyperammonemic coma

A child with carbamyl-phosphate-synthetase defect who died after prolonged continuous hemodiafiltration in deep coma proved to have high aminoacid losses despite aminoacid infusion. We think that this results from high small-solute clearance during hemodialysis. In order to prevent these inevitable catabolic side-effects we decided to add aminoacids to the dialysate and substitution fluid in these children with metabolic diseases. Additionally we propose to add phosphate in order to avoid depletion. The aim is to achieve anabolic or at least non-catabolic hemodiafiltration.

Renal insufficiency in the neonatal period

Prevalence of renal insufficiency and renal failure of newborns in an intensive care unit is considerably high. Most patients have prerenal failure which is associated with the underlying disease, some have had heart surgery and only few patients have congenital renal malformation. In a retrospective analysis in our institution main risk factors were: prematurity, age < 10 days, obstetric complications, male gender, Cesarean delivery and pulmonary disease. We could not confirm, however, that asphyxia is significant for renal failure. Much more common than manifest renal failure is renal insufficiency in diseased newborns during intensive care. The cause is sometimes primary renal insufficiency as a harbinger of renal failure, but it is often iatrogenic, because fluid intake is inadequate, either unintentional or for a purpose. This strategy, however, conflicts with a conservative approach to renal insufficiency, which requires adequate fluid and caloric intake. A skilled approach to this situation demands a daily re-evaluation of the fluid regimen with regard to possible liberalization. If renal failure progresses dialysis may be indicated, but this remains controversial in neonates. However, with growing expertise, skill and adequate equipment, different techniques of dialysis nowadays can be applied even to small infants. Mortality in infants with acute renal failure ranges from 25 to 78%, but death is seldom caused primarily by renal disease. In our survey 0.9% in a total of 34% mortality was attributed to renal disease. Attention has to be paid to the bulk of diseased newborns, who experience only slight increase in serum creatinine in their early life with only mild (or even without) oliguria, who may be prone to residual renal morbidity as well as those, who have manifest renal failure.

[25 years kidney replacement therapy in childhood and adolescence--success of somatic and psychosocial rehabilitation]

In the late sixties, renal replacement therapy (RRT) was started in terminal renal insufficient children and adolescents. The high mortality rate and extreme therapeutic difficulties gave doubts to the possibility of longterm survival as well as somatic and psychosocial rehabilitation in these patients. But nowadays due to improvements in medical and technical possibilities of dialysis and kidney transplantation as well as to individually adapted treatment of the metabolic problems 5-years survival rate is more than 90%, body growth and development is in the lower normal range. Successful psychosocial rehabilitation despite RRT has also improved over time. In the beginning only 29% dialysed patients and 51% transplanted children attended school and 65% completed school. A recent analysis of educational status employment rate and social situation in 617 patients between 20 and 35 year of age who started RRT as children in Europe and 276 terminal renal insufficient adolescents in Germany, gave following results: one third went to vocational training, 11-17% attended university. Thereafter 40-65% of all patients were employed. Unemployment was a big problem in dialysed adolescents and young adults. With increasing age the patients gained independence in their life style. About 20% lived in their own houses, 28% were either married, divorced or widowed, 8% had children of their own.

[Interdisciplinary management of fetal obstructive uropathy]

The joint care of children with obstructive uropathy by perinatologists, pediatric intensivists, pediatric nephrologists and urologists can preserve as much renal function as possible. Complications such as urinary tract infections and problems with renal insufficiency can be prevented. Preterm delivery for early surgical decompression of the urinary tract postpartal should be performed only in exceptional cases. We want to underline that supporting and counselling parents in coping with severe findings and prognosis of the disease is among our main aims. We will present two selected cases to demonstrate the spectrum of methods for handling fetal obstructive uropathy.

[Management of children with prenatally diagnosed urinary tract abnormalities]

Between 1984 and 1991, antenatal ultrasound scanning detected urinary tract malformations in 126 infants, who were investigated and treated postnatally in the childrens' hospital of the Westfälische Wilhelms-University Münster. 10 out of 126 children with urogenital changes, died in the first hours after birth, due to pulmonary hypoplasia (Potter's sequence), 1 further infant died later after cardiac operation, and another died of megacystic-megaureter-hypoperistaltic-syndrome. In the first months after birth 71 (61%) of 116 infants underwent urological surgery; 12/116 infants (10.3%) had severe bilateral kidney changes, some of them with severe deficiency of amniotic fluid before birth. 6/116 infants (5.2%) had chronic renal insufficiency, 2 of them will have to be dialyzed in early childhood and longterm, 14 patients (12%) are threatened by chronic renal failure. 14 patients (12%) developed severe arterial hypertension, all had to be treated with antihypertensive drugs, in 5 of them hypertension subsided after unilateral nephrectomy, another five had transient hypertension, but four require continued medical treatment. We describe the prenatal ultrasound findings, compared them with diagnosis after birth, illustrate diagnostics, plans of therapy, urological surgical interventions and nephrological consequences. Benefits and limitations of antenatal ultrasonography for the detection of urinary tract malformations and the treatment of those malformations before and after birth are discussed. In utero diagnosis of severe urinary tract abnormalities allows treatment of these infants immediately after birth, furthermore the prevention of severe infections, additional damage of renal tissue, and early diagnosis and treatment of arterial hypertension and metabolic imbalances caused by chronic renal insufficiency in early childhood.

Psychosocial adaptation of children and adolescents with chronic renal failure

In a multicentre study comprising five paediatric nephrology centres in Western Germany, psychosocial and educational parameters were assessed (during 1987) in 479 children and adolescents with chronic renal failure (CRF) in order to gain insight into their psychosocial adaptation to the disease. At the time of assessment, 31% of patients were on conservative treatment, 14% on haemodialysis, 9% on continuous ambulatory peritoneal dialysis and 46% had a functioning transplant. The mean age at assessment was 13.6 years. Additional disabilities were noted in 29% of patients. School attendance of the 233 children of school age was in general satisfactory; 22% of patients attended schools for disabled or handicapped children. Vocational training was frequently inadequate, especially for dialysed patients, and only 14 of 53 adolescents over 16 years had graduated. Of 49 adult patients, only 21 were in some form of employment. A lack of age-appropriate independence was observed in a large proportion (86%) of patients over 17 years, who continued to live with their parents or other persons taking care of them, whilst only 14% were living alone or with a partner. We conclude that, despite improved survival, psychosocial adaptation continues to be impaired in paediatric patients with CRF, especially in adolescents and those on dialysis.

[Arterial hypertension. Prevention in infants with congenital urinary tract malformations]

Eighty-nine newborns and infants with congenital urinary tract malformations were treated in the childrens' hospital of the Westfälische Wilhelms-University from 1986 to 1989. Twenty patients of this group (22.5%) developed severe hypertension requiring treatment within the first year of life. Mean age of diagnosis of hypertension was 5 months (range 0.5-12 months). Median values for blood pressure at time of diagnosis were 138 mmHg (range 120-170) for systolic and 92 mmHg (range 80-110) for diastolic values. Six patients showed characteristic symptoms for hypertension such as restlessness, sweating and sleep disorders. Plasma levels of renin were obtained in 12 of 20 patients. Five patients had raised plasma renin levels. All patients with a severe hypertension were treated with one to several antihypertensive drugs. Risk factors for the development of severe renal hypertension in early infancy are cystic renal malformation, vesico-ureteral reflux, obstructive uropathy and to our experience also short term percutaneous nephrostomy in obstructive uropathy in particular in connection with pyelonephritis. Hypertension can still appear after the successful surgical correction of urinary obstruction. We describe the group of patients with severe hypertension in our study group; diagnostic principles and our therapeutic approach are explained. We conclude that early diagnosis of severe hypertension and consecutive treatment are important in infants with congenital urinary malformations.

[Autosomal dominant polycystic kidney disease in infancy]

We report on a 6 months old infant with suddenly developed severe arterial hypertension caused by polycystic kidneys. Examinations of the relatives revealed similar changes of the kidneys in 4 adults and 5 children. They were all diagnosed to have autosomal dominant polycystic kidney disease. Excretory kidney function of all patients is normal; however, blood pressure was raised in the adults. We would like to stress the importance of family screening in this disease, in particular with regard to possible early diagnosis and treatment of arterial hypertension. The long-term prognosis of the early manifestation of the dominantly inherited cystic kidney disease is uncertain.