Mutations in the tight-junction gene claudin 19 (CLDN19) are associated with renal magnesium wasting, renal failure, and severe ocular involvement

Claudins are major components of tight junctions and contribute to the epithelial-barrier function by restricting free diffusion of solutes through the paracellular pathway. We have mapped a new locus for recessive renal magnesium loss on chromosome 1p34.2 and have identified mutations in CLDN19, a member of the claudin multigene family, in patients affected by hypomagnesemia, renal failure, and severe ocular abnormalities. CLDN19 encodes the tight-junction protein claudin-19, and we demonstrate high expression of CLDN19 in renal tubules and the retina. The identified mutations interfere severely with either cell-membrane trafficking or the assembly of the claudin-19 protein. The identification of CLDN19 mutations in patients with chronic renal failure and severe visual impairment supports the fundamental role of claudin-19 for normal renal tubular function and undisturbed organization and development of the retina.

Autosomal Dominant Pseudohypoaldosteronism Type 1: Mechanisms, Evidence for Neonatal Lethality, and Phenotypic Expression in Adults

Autosomal dominant pseudohypoaldosteronism type 1 (adPHA1) is a rare condition that is characterized by renal resistance to aldosterone, with salt wasting, hyperkalemia, and metabolic acidosis. It is thought of as a mild disorder; affected children's symptoms respond promptly to salt therapy, and treatment is not required after childhood. Mutations in the mineralocorticoid receptor gene (MR) cause adPHA1, but the long-term consequences of MR deficiency in humans are not known. Herein are described six novel adPHA1-causing MR mutations (four de novo) and evidence that haploinsufficiency of MR is sufficient to cause adPHA1. Furthermore, genotype-phenotype correlation is reported in a large adPHA1 kindred. A number of cases of neonatal mortality in infants who were at risk for adPHA1 were identified; coupled with the frequent identification of de novo mutations in affected individuals, this suggests that the seemingly benign adPHA1 may have been a fatal neonatal disorder in previous eras, preventing propagation of disease alleles. In contrast, it is shown that adult patients with adPHA1 are clinically indistinguishable from their wild-type relatives except for presumably lifelong elevation of renin, angiotensin II, and aldosterone levels. These data highlight the critical role of MR in the maintenance of salt homeostasis early in life and illuminate the sodium dependence of pathologic effects of renin and angiotensin II. They furthermore argue that nongenomic effects of aldosterone play no significant role in the long-term development of cardiovascular disease.

Acidosis increases magnesiuria in children with distal renal tubular acidosis

In experimental animals, metabolic acidosis increases renal magnesium (Mg) excretion, whereas metabolic alkalosis reduces it. The objective of this study was to examine renal magnesium handling (U(Mg)) in children with primary distal renal tubular acidosis (DRTA). We measured U(Mg) in 11 children (3 females, 8 males, aged 6.9+/-4.9 years) with primary DRTA. They were studied either during spontaneous acidosis post treatment removal (3 patients) or after ammonium chloride (100 mmol/m2) induced acidosis (8 patients), and then following oral sodium bicarbonate load (4 g/1.73 m2). During acidosis (plasma pH 7.28+/-0.09, bicarbonate 13.2+/-4.3 mEq/l), U(Mg) was elevated (U(Mg/Cr) 0.18+/-0.06 mg/mg, normal values 0.1+/-0.06, P=0.003) although plasma Mg (P(Mg)) was in the normal range (1.93+/-0.31 mg/dl, controls 1.77+/-0.19, P=NS). After acute correction of metabolic acidosis (plasma pH 7.44+/-0.05, bicarbonate 25.6+/-1.6 mEq/l, P<0.001; urine pH 7.52+/-0.28, bicarbonate 86.9+/-39.1 mEq/l), U(Mg) decreased significantly (P=0.003), returning to control values after about 2 h (U(Mg/Cr) 0.09+/-0.06 mg/mg). Bicarbonate load resulted not only in reduction in U(Mg) but also in a decrease in urinary calcium excretion (U(Ca/Cr)) from 0.46+/-0.17 mg/mg to 0.14+/-0.12 mg/mg (P<0.001). We conclude that in children with primary DRTA, urinary Mg excretion is markedly increased and that this defect, like the hypercalciuric defect, is correctable by sodium bicarbonate administration.

Paracellin-1, a renal tight junction protein required for paracellular Mg2+ resorption

Epithelia permit selective and regulated flux from apical to basolateral surfaces by transcellular passage through cells or paracellular flux between cells. Tight junctions constitute the barrier to paracellular conductance; however, little is known about the specific molecules that mediate paracellular permeabilities. Renal magnesium ion (Mg2+) resorption occurs predominantly through a paracellular conductance in the thick ascending limb of Henle (TAL). Here, positional cloning has identified a human gene, paracellin-1 (PCLN-1), mutations in which cause renal Mg2+ wasting. PCLN-1 is located in tight junctions of the TAL and is related to the claudin family of tight junction proteins. These findings provide insight into Mg2+ homeostasis, demonstrate the role of a tight junction protein in human disease, and identify an essential component of a selective paracellular conductance.

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.

Mutations in the mineralocorticoid receptor gene cause autosomal dominant pseudohypoaldosteronism type I

Pseudohypoaldosteronism type I (PHA1) is characterized by neonatal renal salt wasting with dehydration, hypotension, hyperkalaemia and metabolic acidosis, despite elevated aldosterone levels. Two forms of PHA1 exist. An autosomal recessive form features severe disease with manifestations persisting into adulthood. This form is caused by loss-of-function mutations in genes encoding subunits of the amiloride-sensitive epithelial sodium channel (ENaC; refs 2,3). Autosomal dominant or sporadic PHA1 is a milder disease that remits with age. Among six dominant and seven sporadic PHA1 kindreds, we have found no ENaC gene mutations, implicating mutations in other genes. As ENaC activity in the kidney is regulated by the steroid hormone aldosterone acting through the mineralocorticoid receptor, we have screened the mineralocorticoid receptor gene (MLR) for variants and have identified heterozygous mutations in one sporadic and four dominant kindreds. These include two frameshift mutations (one a de novo mutation), two premature termination codons and one splice donor mutation. These mutations segregate with PHA1 and are not found in unaffected subjects. These findings demonstrate that heterozygous MLR mutations cause PHA1, underscore the important role of mineralocorticoid receptor function in regulation of salt and blood pressure homeostasis in humans and motivate further study of this gene for a potential role in blood pressure variation.

A randomized comparison of surfactant dosing via a dual-lumen endotracheal tube in respiratory distress syndrome. The Spanish Surfactant Collaborative Group

AIM

To determine if 1-minute instillation of Curosurf via a dual-lumen endotracheal tube without interruption of mechanical ventilation could decrease the incidence of hypoxia (drop in oxygen saturation [SaO2] to <80%, or of transcutaneous partial pressure of oxygen [PtcO2] to <50 mm Hg [6.6 kPa]) and bradycardia (heart rate below 80 beats/minute) at dosing, without affecting the efficacy of the standard bolus delivery.

DESIGN

Prospective, multicenter, randomized, nonblinded clinical trial.

SETTING

Neonatal intensive care units of the Spanish Surfactant Collaborative Group.

PATIENTS AND METHODS

One hundred ninety-eight infants (birth weight 600-2000 g) with respiratory distress syndrome needing mechanical ventilation with a fraction of inspired oxygen [FIO2] 0.40 were randomized before 24 hours to receive 200 mg/kg of Curosurf, either by bolus instillation (n = 99) or by a simplified dosing technique (n = 99), giving the full dose in 1 minute via a dual-lumen endotracheal tube without positioning, interruption of mechanical ventilation, or bagging. Two additional doses (100 mg/kg) were given within 12 and 24 hours of first dose, by the same method, if the infant still needed mechanical ventilation and had a FIO2 0.30. The effects of both procedures on the incidence of acute adverse events at dosing, gas exchange, ventilator requirements, and outcome at 28 days were compared.

RESULTS

Fewer episodes of hypoxia (18 vs 40% of doses), and a smaller decrease in heart rate and SaO2 were observed in the dual-lumen group. Efficacy of surfactant, based on improvement of oxygenation, ventilator requirements, and number of doses required, was similar in both groups. Infants in the dual-lumen group had a lower total time exposure to supplemental oxygen (195+/-199 vs 266+/-221 hours). No differences in the incidence of air leaks, intraventricular hemorrhage, patent ductus arteriosus, bronchopulmonary dysplasia, or survival were observed.

CONCLUSION

A simplified 1-minute Curosurf dosing procedure via a dual-lumen endotracheal tube without fractional doses, ventilator disconnection, changes in the infant's position, or manual bagging was found to reduce the number of dosing-related adverse transient episodes of hypoxia. Although the simplified method appeared to be as effective as bolus delivery, this should be confirmed in a larger trial.

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.

Acute and chronic effects of cisplatin therapy on renal magnesium homeostasis

Although the acute renal toxicity of cisplatin has been well documented, long-term follow-up studies in cisplatin-treated children are scanty. We have evaluated the incidence and characteristics of both acute and chronic nephrotoxicity in 22 children (median age 8 years) treated with cisplatin as part of different chemotherapeutic protocols. All patients exhibited a significant and progressive decrease in plasma magnesium (Mg) values soon after cisplatin administration. Magnesiuria also increased immediately after therapy. Hypomagnesemia (plasma Mg < 1.4 mg/dl) occurred in 10 patients and it was dose-dependent. Minimal and mean cumulated doses inducing hypomagnesemia were 300 and 500 mg/m2, respectively. In 18 children we followed renal function prospectively for a mean time of 2.3 years after arrest of cisplatin therapy. Chronic hypomagnesemia and moderate elevation of plasma creatinine were observed in 6 children, hypocalciuria in 5 children, and hypokalemia in 1 child. Presence of hypomagnesemia was unrelated to the total dose received or the time elapsed since cisplatin therapy. Renal function studies, performed in the 6 children with chronic hypomagnesemia, revealed different degrees of impairment in Mg reabsorption. The functional characteristics of chronic cisplatin nephrotoxicity found in the present series-contrary to prior reports-are not comparable to those present in the inherited Gitelman's syndrome.

Genetic heterogeneity of Bartter's syndrome revealed by mutations in the K+ channel, ROMK

Mutations in the Na-K-2Cl cotransporter (NKCC2), a mediator of renal salt reabsorption, cause Bartter's syndrome, featuring salt wasting, hypokalaemic alkalosis, hypercalciuria and low blood pressure. NKCC2 mutations can be excluded in some Bartter's kindreds, prompting examination of regulators of cotransporter activity. One regulator is believed to be ROMK, an ATP-sensitive K+ channel that 'recycles' reabsorbed K+ back to the tubule lumen. Examination of the ROMK gene reveals mutations that co-segregate with the disease and disrupt ROMK function in four Bartter's kindreds. Our findings establish the genetic heterogeneity of Bartter's syndrome, and demonstrate the physiologic role of ROMK in vivo.

Hypogonadotrophic hypogonadism with hyposmia, X-linked ichthyosis, and renal malformation syndrome

OBJECTIVE

The aim of this study was the endocrinological, enzymatic, and genetic evaluation of a family with a complex syndrome associating hypogonadotrophic hypogonadism with hyposmia, X-linked ichthyosis and renal malformation.

DESIGN

Hypothalamic-pituitary-testicular function, olfaction, steroid sulphatase activity, and morphological renal studies were assessed. DNA molecular analyses were carried out in all the patients.

PATIENTS

Two brothers and their maternal uncle showed the clinical picture of congenital ichthyosis, hypogonadism, hyposmia and unilateral renal maldevelopment.

MEASUREMENTS

LH and FSH were determined by RIA basally and after GnRH stimulation, and the test repeated after a period of GnRH priming. Testosterone response to hCG was measured. Arylsulphatase C assay was performed as a measure of steroid sulphatase activity. DNA amplification analysis and Southern blot analysis of four Xp22.3 loci were performed.

RESULTS

Low levels of gonadotophins, basally and after acute GnRH, increased clearly after GnRH priming. Low testosterone levels increased promptly after hCG. Subnormal levels of arylsulphatase C were detected. Hyposmia and renal hypoplasia or aplasia were demonstrated. A large Xp 22.3 deletion including the genes responsible for X-linked ichthyosis (steroid sulphatase deficiency) and Kallmann syndrome was demonstrated.

CONCLUSIONS

The absence of the gene encoding steroid sulphatase accounts for the X-linked ichthyosis in these patients, whereas the absence of the Kallmann syndrome gene accounts for hypogonadism, anosmia and for the single kidney found in two of the three patients.

Chloride deficiency as a presentation or complication of cystic fibrosis

Thirteen children with cystic fibrosis (CF), aged 1.5 months-15 years, had 18 episodes of hypochloraemia and metabolic alkalosis over the period 1983-1991. Five patients were not known to have CF prior to developing these electrolyte disturbances. There were two distinct clinical presentations: 5 patients had an acute isolated picture of heat exhaustion while 8 patients (all infants) had a more chronic course associated with failure to thrive. Many episodes were not associated with particularly high environmental temperatures, although most occurred during the summer and early autumn months. Serum electrolytes should be assessed regularly in children with CF, and this diagnosis should be considered in any infant presenting with unexplained hypochloraemic metabolic alkalosis.

Use of serological markers as a screening test in family members of patients with celiac disease

That symptomatic celiac disease (CD) can occur in several members of a family has long been recognized. Given the possible complications of untreated CD, it is also important to diagnose those family members with "silent" disease, to offer them the benefit of a gluten-free diet. We studied 642 first-degree relatives of 210 patients with CD, two of the latter belonging to the same family. IgA and IgG antigliadin antibodies and IgA antiendomysium antibodies were studied in all. Jejunal biopsy was performed in 59 subjects, 47 with positive and 12 with negative serological markers. Celiac disease was diagnosed de novo in 18 cases (2.8%). Diagnosis in a symptomatic mother was made by jejunal biopsy despite the negativity of all immunological markers. We conclude that the risk of having CD is higher in siblings than in parents of patients with CD, that the most useful marker for diagnosis is the study of IgA antiendomysium antibodies, and that the absence of positive serological markers does not completely exclude the diagnosis of CD.

Autologous mixed lymphocyte reaction and T-cell suppressor activity in patients with Henoch-Schönlein purpura and IgA nephropathy

To assess the existence of persistent abnormalities in the cellular mechanisms regulating the immunoglobulin (Ig) synthesis in Henoch-Schönlein purpura (HSP) and IgA nephropathy, we studied through a hemolytic plaque assay (PFC) the response to the autologous mixed lymphocyte reaction (AMLR) and the T-cell suppressor activity in 24 patients with IgA nephropathy, in 20 individuals with inactive HSP (IHSP) and in 18 normal controls. In the group with IgA nephropathy there was a significant increase in the number of IgA-secreting cells after AMLR (p less than 0.01), and 9 of the 15 patients tested had an impaired generation of T-cell suppressor activity. No such abnormalities were found in individuals with IHSP. These findings support the existence of persistent defect in the mechanisms regulating the Ig synthesis, limited only to the patients with IgA nephropathy.

Plasma fatty acid composition during the first week of life following feeding with human milk or formula

Plasma fatty acids were studied in 20 full-term newborn infants fed human milk and in 17 newborn infants of identical characteristics fed an adapted cow's milk formula. Plasma fatty acids were measured in cord blood and at 7-9 days of age. No differences were present at birth but, after a period of feeding, infants receiving breast milk had higher plasma concentrations of stearic acid, di-homo-gamma-linolenic acid and arachidonic acid, while infants receiving formula had a higher plasma concentration of oleic acid. The importance of these findings in relation to the lipidic structure of the nervous system remains to be determined.

Biochemical features of dietary chloride deficiency syndrome: a comparative study of 30 cases

The diagnosis in one infant of a severe state of chloride deficiency after ingesting a diet consisting exclusively of a modified cow milk formula containing only 0.5 mEq/100 kcal chloride ion led to the identification of 30 additional infants (age 2.6 +/- 0.7 months) fed the same commercial formula. The total absence of chloride in the urine was used as a biochemical index of subclinical dietary chloride deficiency. Serum and urine values were studied at diagnosis and 10 to 12 days after chloride replenishment, and compared statistically with the values obtained in a control group of 40 infants (age 2.8 +/- 1.2 months) fed exclusively a different modified formula containing an adequate chloride concentration. The outstanding laboratory abnormalities noted in the infants ingesting a low chloride formula were hypochloremia and metabolic alkalosis. Mean serum concentrations of potassium, urea, creatinine, and uric acid were in the normal range, but group values were statistically different from normal. A previously unreported finding was the demonstration of a significant elevation in the serum concentrations of calcium and phosphate and in the urinary excretions of calcium and magnesium, which persisted after almost complete recovery of the remaining biochemical disturbances. These results indicate the potential risk of nephrocalcinosis after dietary chloride deficiency.

Natural history of primary distal renal tubular acidosis treated since infancy

Clinical and pathophysiologic studies were performed in five unrelated children with primary distal renal tubular acidosis who were diagnosed during infancy and followed for 3 to 9 1/2 years. All patients had permanent defects in hydrogen ion secretion, sodium reabsorption, and concentrating capacity. A transient, age-related, proximal tubular defect in sodium and bicarbonate reabsorption was also present. Renal bicarbonate wasting was mainly observed during the first years of life and progressively decreased with advancing age. Glomerular filtration rate remained within normal limits. Following sustained therapy with sodium and potassium bicarbonate, the patients had optimal growth, arrest of progression of nephrocalcinosis, and lack of other characteristic features of the disease with the exception of polyuria. Dosage of alkali was mainly determined by the magnitude of the renal bicarbonate loss and decreased progressively from a maximum of 3.9 to 10.0 mEq/kg/day during the first year of life to about 3 mEq/kg/day at or beyond 6 years of age. The total dosage of alkali required could be derived by the sum of the urinary excretion of bicarbonate plus 2 mEq/kg/day, which represents mean endogenous acid production. Although calciuria was normal when metabolic acidosis was corrected, patients with higher urinary sodium excretion had higher urinary excretion of calcium and thus were at greater risk of developing nephrocalcinosis if therapy was not carefully controlled.

Enteropathy related to fish, rice, and chicken

Gastrointestinal symptoms in relation to the ingestion of proteins are common but only in the case of sensitisation to cows' milk protein, soy, or gluten have alterations in the function and structure of the small-intestine been reported. We describe 3 children with cows' milk protein intolerance and associated enteropathy related to fish, rice, and chicken, respectively. Repeated intestinal biopsies before and after an acute challenge with the specific food showed changes in the histological appearance of the intestinal mucosa identical with those observed after the acute administration of cows' milk. These findings support the conclusion that cows' milk-protein intolerance is not an isolated entity; it represents the first part of a broader intolerance of various dietary proteins.

Defect in urinary acidification in nephrotic syndrome and its correction by furosemide

6 children with idiopathic nephrotic syndrome were investigated during clinical relapse to examine the interrelation between distal urinary acidification and urinary sodium excretion. Blood and urine studies were initiated 4 h after completion of ammonium chloride loading, prior to and following the intravenous administration of furosemide. Values for plasma bicarbonate before and after furosemide administration were not significantly different. In the control periods, when urinary sodium excretion was very low, a defect in urinary acidification was demonstrated (UPH: 6.09 +/- (SD) 0.27; UTAV and UNH4V: 12.6 +/- 3.1 and 36.4 +/- 15.8 mumol/min/1.73 m2, respectively.) Following furosemide-induced natriuresis UPH fell to 4.81 +/- 0.25 (p less than 0.0005), and UTA2V and UNH4V increased to 46.3 +/- 15.8 and 125.6 +/- 49.5 mumol/min/1.73 m2, respectively (p less than 0.002). No overall correlation existed between urinary acidity, both considered as hydrogen ion concentration and as hydrogen ion excretion, and rate of urinary sodium excretion; but significant correlations were present between hydrogen ion concentration in the urine and both UC1V-UNAV (r = 0.38, p less than 0.05), and UC1V - (UNaV + UKV) (r = 0.64, p less than 0.01). These results indicate that the defect in distal urinary acidification observed in nephrotic syndrome is probably due to decreased delivery of sodium to the distal nephron. The enhanced secretion of hydrogen ion observed after furosemide administration may be related both to increased sodium delivery and to greater sodium than chloride reabsorption in the collecting duct.

Juvenile cirrhosis and membranous glomerulonephritis in a child with alpha1-antitrypsin deficiency PiSZ

An infant with alpha1-antitrypsin (alpha1-AT) deficiency PiSZ presented with liver cirrhosis and showed clinical and laboratory evidence of renal disease when hepatic decompensation developed, shortly before death at 12 months of age. Low serum levels of alpha1-AT were only demonstrated late in the disease. SZ phenotype was proved by starch gel electrophoresis. Post-mortem pathological studies revealed severe hepatic cirrhosis with intracytoplasmic inclusion of alpha1-AT and membranous glomerulonephritis with deposits of complement and immunoglobulins but without the presence of alpha1-AT. The present case suggests the importance of studying Pi phenotypes and serum levels of alpha1-AT in all cases of idiopathic cirrhosis or renal disease in infancy.

Bartter's syndrome presenting with features resembling renal tubular acidosis. Improvement of renal tubular defects by indomethacin

A 2-year-old girl presenting with features of both Bartter's syndrome and renal tubular acidosis was investigated. Hypokalemia, increased plasma renin activity in the absence of hypertension, insensitivity to the pressor effects of angiotensin and a histological picture of juxtaglomerular hyperplasia were characteristic of Bartter's syndrome, but an unusual finding was the presence of metabolic acidosis instead of alkalosis. Functional studies revealed a proximal tubular defect in sodium and bicarbonate reabsorption and a distal defect in sodium reabsorption, urinary acidification and concentrating mechanism. Indomethacin administration was followed by an excellent clinical response and improvement of most functional abnormalities. The defect in distal sodium reabsorption was, however, not corrected by prostaglandin inhibition, and could represent the primary event leading to potassium wasting and secondary hypersecretion of prostaglandins.

Proximal renal tubular acidosis in metachromatic leukodystrophy

A 2-year-old girl affected with the late infantile form of metachromatic leukodystrophy had a persistent and moderate metabolic acidosis. Renal functional studies demonstrated the presence of decreased tubular reabsorption of sodium, bicarbonate and some amino acids. Other tubular functions, including distal urinary acidification and concentrating mechanism were normal. Glomerular filtration rate was moderately decreased. Metachromatic inclusions were demonstrated along the nephron by histochemistry and electron microscopy. Tubular dysfunction in metachromatic leukodystrophy could have been overlooked until now given the severity of the neurological picture.

Proximal renal tubular acidosis in the tetralogy of fallot

A 9-year-old girl presented with tetralogy of Fallot and moderate metabolic acidosis. Despite a Blalock's fistula there was evidence of chronic hypoxia with cyanosis, clubbing of fingers and toes and very elevated blood hematocrit values. Renal acidification and bicarbonate titration demonstrated the existence of proximal renal tubular acidosis: renal bicarbonate threshold was low (18 mmoles/1) and normal urinary acidificaiton was present at subthreshold serum bicarbonate levels. Following corrective heart surgery, blood acid-base values and renal reabsorption of bicarbonate became normal. A causal relationship between extracellular fluid volume expansion dependent on the high hematocrit and proximal renal tubular acidosis is suggested.

Distal renal tubular acidosis in infancy: a bicarbonate wasting state

Three unrelated infants with apparently distal RTA were investigated. Growth retardation, polyuria, nephrocalcinosis, inappropriately high urinary pH, and marked dependence of bicarbonate excretion on urinary flow were characteristic of the distal or classic form of RTA, but the urinary loss of bicarbonate at normal serum values exceeded that usually found in children or adults with this disorder. Renal tubular function was studied during hypotonic saline diuresis in the three patients and in seven healthy control infants of similar age. Fractional delivery of sodium to the distal nephron was significantly higher in the patients than in control subjects. Sodium transport at the diluting segment was not impaired. The results support the assumption that the bicarbonate wasting was the consequence of an increased delivery of this substance to an already impaired distal nephron and thus further inhibited the distal mechanisms of net acid excretion.