Alberto Bettinelli

Mutations in Kelch-like 3 and Cullin 3 cause hypertension and electrolyte abnormalities

Hypertension affects one billion people and is a principal reversible risk factor for cardiovascular disease. Pseudohypoaldosteronism type II (PHAII), a rare Mendelian syndrome featuring hypertension, hyperkalaemia and metabolic acidosis, has revealed previously unrecognized physiology orchestrating the balance between renal salt reabsorption and K+ and H+ excretion. Here we used exome sequencing to identify mutations in kelch-like 3 (KLHL3) or cullin 3 (CUL3) in PHAII patients from 41 unrelated families. KLHL3 mutations are either recessive or dominant, whereas CUL3 mutations are dominant and predominantly de novo. CUL3 and BTB-domain-containing kelch proteins such as KLHL3 are components of cullin–RING E3 ligase complexes that ubiquitinate substrates bound to kelch propeller domains. Dominant KLHL3 mutations are clustered in short segments within the kelch propeller and BTB domains implicated in substrate and cullin binding, respectively. Diverse CUL3 mutations all result in skipping of exon 9, producing an in-frame deletion. Because dominant KLHL3 and CUL3 mutations both phenocopy recessive loss-of-function KLHL3 mutations, they may abrogate ubiquitination of KLHL3 substrates. Disease features are reversed by thiazide diuretics, which inhibit the Na–Cl cotransporter in the distal nephron of the kidney; KLHL3 and CUL3 are expressed in this location, suggesting a mechanistic link between KLHL3 and CUL3 mutations, increased Na–Cl reabsorption, and disease pathogenesis. These findings demonstrate the utility of exome sequencing in disease gene identification despite the combined complexities of locus heterogeneity, mixed models of transmission and frequent de novo mutation, and establish a fundamental role for KLHL3 and CUL3 in blood pressure, K+ and pH homeostasis.

Use of calcium excretion values to distinguish two forms of primary renal tubular hypokalemic alkalosis: Bartter and Gitelman syndromes.

Clinical or biochemical findings were reevaluated in 34 pediatric patients with primary renal tubular hypokalemic metabolic alkalosis. The patients were subdivided into two groups. Bartter syndrome (primary renal tubular hypokalemic metabolic alkalosis with normocalciuria or hypercalciuria) was diagnosed in 18 patients with molar urinary calcium/creatinine ratios greater than 0.20, and Gitelman syndrome (primary renal tubular hypokalemic metabolic alkalosis with magnesium deficiency and hypocalciuria) was diagnosed in 16 patients with molar urinary calcium/creatinine ratios less than or equal to 0.20 and plasma magnesium levels less than 0.75 mmol/L. Some clinically important differences between the groups were observed. Patients with Bartter syndrome were often born after pregnancies complicated by polyhydramnios (8/18) or premature delivery (7/18) and had short stature (11/18) or polyuria, polydipsia, and a tendency to dehydration (16/18) during infancy (12/18) or before school age (18/18). Patients with Gitelman syndrome had tetanic episodes (12/16) or short stature (3/16) at school age (14/16). We conclude that the Bartter and Gitelman syndromes represent two distinct variants of primary renal tubular hypokalemic metabolic alkalosis and are easily distinguished on the basis of urinary calcium levels.

Phenotypic variability in Bartter syndrome type I

Abstract Limited phenotypic variability has been reported in patients with Bartter syndrome type I, with mutations in the Na-K-2Cl cotransporter gene (BSC). The diagnosis of this hereditary renal tubular disorder is usually made in the antenatal-neonatal period, due to the presence of polyhydramnios, premature delivery, hypokalemia, metabolic alkalosis, hypercalciuria, and nephrocalcinosis. Among nine children with hypercalciuria and nephrocalcinosis, we identified new mutations consistent with a loss of function of the mutant allele of the BSC gene in five. Three of the five cases with BSC gene mutations were unusual due to the absence of hypokalemia and metabolic alkalosis in the first years of life. The diagnosis of incomplete distal renal tubular acidosis was considered before molecular evaluation. Three additional patients with hypokalemia and hypercalciuria, but without nephrocalcinosis in the first two and with metabolic acidosis instead of alkalosis in the third, were studied. Two demonstrated the same missense mutation A555T in the BSC gene as one patient of the previous group, suggesting a single common ancestor. The third patient presented with severe hypernatremia and hyperchloremia for about 2 months, and a diagnosis of nephrogenic diabetes insipidus was hypothesized until the diagnosis of Bartter syndrome type I was established by molecular evaluation. We conclude that in some patients with Bartter syndrome type I, hypokalemia and/or metabolic alkalosis may be absent in the first years of life and persistent metabolic acidosis or hypernatremia and hyperchloremia may also be present. Molecular evaluation can definitely establish the diagnosis of atypical cases of this complex hereditary tubular disorder, which, in our experience, may exhibit phenotypic variability.

Risk factors for poor renal prognosis in children with hemolytic uremic syndrome

Many factors have been proposed as predictors of poor renal prognosis in children with hemolytic uremic syndrome (HUS), but their role is still controversial. Our aim was to detect the most reliable early predictors of poor renal prognosis to promptly identify children at major risk of bad outcome who could eventually benefit from early specific treatments, such as plasmapheresis. Prognostic factors identifiable at onset of HUS were evaluated by survival analysis and a proportional hazard model. These included age at onset, prodromal diarrhea (D), leukocyte count, central nervous system (CNS) involvement, and evidence of Shiga toxin-producing Escherichia coli (STEC) infection. Three hundred and eighty-seven HUS cases were reported; 276 were investigated for STEC infection and 189 (68%) proved positive. Age at onset, leukocyte count, and CNS involvement were not associated with the time to recovery. Absence of prodromal D and lack of evidence of STEC infection were independently associated with a poor renal prognosis; only 34% of patients D−STEC− recovered normal renal function compared with 65%–76% of D+STEC+, D+STEC− and D−STEC+ patients. In conclusion, absence of both D and evidence of STEC infection are needed to identify patients with HUS and worst prognosis, while D– but STEC+ patients have a significantly better prognosis.

Normal prostaglandinuria E2 in Gitelman's syndrome, the hypocalciuric variant of Bartter's syndrome

In familial Bartters syndrome, hyperprostaglandinuria is considered a constant feature and prostanoid synthetase inhibition often positively influences the disease course. The urinary calcium excretion distinguishes two clinically and biochemically different variants, namely, classic Bartters syndrome (normocalciuric or hypercalciuric variant; urinary calcium to creatinine > or = 35.3 mg/mg 10(-3)) and Gitelmans syndrome (hypocalciuric variant; urinary calcium to creatinine < 35.3 mg/mg 10(-3)). In the hypocalciuric variant of Bartters syndrome prostanoid synthetase inhibition is of little benefit. Since the production of prostanoids has not been extensively studied in Gitelmans syndrome, the urinary excretion of prostaglandin E2 was assessed by radioimmunoassay in 11 untreated patients with Gitelmans syndrome (aged 10 to 21 years; five females and six males) and in 11 healthy controls (aged 11 to 20 years; five females and six males). The urinary excretion of prostaglandin E2 was similar in both study groups. The study provides the rationale for the poor effect of prostanoid synthetase inhibition in the hypocalciuric variant of Bartters syndrome. The assessment of urinary excretion of prostaglandin E2 does not represent a diagnostic sine qua non in the context of familial Bartters syndrome.

Body fluids and salt metabolism - Part I.

There is a high frequency of diarrhea and vomiting in childhood. As a consequence the focus of the present review is to recognize the different body fluid compartments, to clinically assess the degree of dehydration, to know how the equilibrium between extracellular fluid and intracellular fluid is maintained, to calculate the effective blood osmolality and discuss both parenteral fluid requirments and repair.

Magnesium supplementation in Gitelman syndrome

Abstract The metabolism of potassium and magnesium are closely linked (in situations where potassium and magnesium depletion coexist, magnesium restoration alone is sufficient to correct hypokalemia). Moreover, magnesium deficiency blunts the interplay between circulating calcium and the calciotropic hormones. Renal magnesium wasting, hypokalemia, alkalosis, hypocalciuria, and a tendency towards hypocalcemia characterize Gitelman syndrome. Plasma or intracellular potassium, circulating calcium, and calciotropic hormones were therefore investigated in eight patients (4 females, 4 males, aged 9–20 years) with Gitelman syndrome before and during oral supplementation with magnesium pyrrolidone carboxylate 30  mmol daily for 4 weeks. Magnesium supplementation significantly increased plasma and intracellular magnesium and plasma calcium, but failed to completely restore magnesium deficiency. In contrast, blood levels of parathyroid hormone and calcitriol and plasma and intracellular potassium were not modified following magnesium administration.

Gitelman Disease Associated with Growth Hormone Deficiency, Disturbances in Vasopressin Secretion and Empty Sella: A New Hereditary Renal Tubular-Pituitary Syndrome?

Gitelman disease was diagnosed in two unrelated children with hypokalemic metabolic alkalosis and growth failure (a boy and a girl aged 7 mo and 9.5 y, respectively, at clinical presentation) on the basis of mutations detected in the gene encoding the thiazide-sensitive NaCl cotransporter of the distal convoluted tubule. GH deficiency was demonstrated by specific diagnostic tests in both children. Hypertonic saline infusion tests showed a partial vasopressin deficiency in the girl and delayed secretion of this hormone in the boy. Magnetic resonance imaging revealed an empty sella in both cases. Up to now, hypomagnesemia and hypocalciuria have been considered obligatory criteria for the diagnosis of Gitelman disease; however, our two patients had hypomagnesia and hypocalciuria in less than half the determinations. GH replacement treatment was associated with a good clinical response in both children. It appears that these cases represent a new phenotype, not previously described in Gitelman disease, and that the entity may be considered a new complex hereditary renal tubular-pituitary syndrome.

Long-term follow-up of patients with Bartter syndrome type I and II

BACKGROUND Little information is available on a long-term follow-up in Bartter syndrome type I and II. METHODS Clinical presentation, treatment and long-term follow-up (5.0-21, median 11 years) were evaluated in 15 Italian patients with homozygous (n = 7) or compound heterozygous (n = 8) mutations in the SLC12A1 (n = 10) or KCNJ1 (n = 5) genes. RESULTS Thirteen new mutations were identified. The 15 children were born pre-term with a normal for gestational age body weight. Medical treatment at the last follow-up control included supplementation with potassium in 13, non-steroidal anti-inflammatory agents in 12 and gastroprotective drugs in five patients. At last follow-up, body weight and height were within normal ranges in the patients. Glomerular filtration rate was <90 mL/min/1.73 m(2) in four patients (one of them with a pathologically increased urinary protein excretion). In three patients, abdominal ultrasound detected gallstones. The group of patients with antenatal Bartter syndrome had a lower renin ratio (P < 0.05) and a higher standard deviation score (SDS) for height (P < 0.05) than a previously studied group of patients with classical Bartter syndrome. CONCLUSIONS Patients with Bartter syndrome type I and II tend to present a satisfactory prognosis after a median follow-up of more than 10 years. Gallstones might represent a new complication of antenatal Bartter syndrome.

Long-term follow-up of a patient with Gitelman's syndrome

The long-term follow-up (from age 6 to 20 years) of a girl with Gitelmans syndrome, who had four hypomagnesaemic-tetanic episodes associated with normal plasma calcium, hypokalaemia and hypocalciuria, is presented. During and after puberty, hypomagnesaemia was of the order of 0.41–0.49 mmol/l and plasma potassium was at the lower reference limit. The long-term clinical course and growth of this patient appeared good, but, magnesium supplementation reduces the risk of tetanic crises.