Distal renal tubular acidosis caused by tryptophan-aspartate repeat domain 72 (WDR72) mutations

Hereditary distal renal tubular acidosis (dRTA) is a rare genetic disease that is caused by mutations in SLC4A1, ATP6V1B1, or ATP6V0A4. However, there are many families with hereditary dRTA in whom the disease-causing genes are unknown. Accordingly, we performed whole exome sequencing and genetic studies of the members of a family with autosomal recessive dRTA of an unknown genetic etiology. Here, we report compound heterozygous pathogenic variations in tryptophan-aspartate repeat domain 72 (WDR72) (c.1777A>G [p.R593G] and c.2522T>A [p.L841Q]) in three affected siblings of a family with dRTA. Both variants segregated with dRTA in the family and were not observed in normal control subjects. Homologous modeling and in silico mutagenesis indicated that R593G and L841Q alter the H-bond formations in the nearby residues, affecting the WDR72 protein structure. All these evidences indicate that the identified WDR72 variations were probably to have caused hereditary dRTA in the reported family. In addition, homozygous nonsense mutation (c.2686C>T [p.R896X]) was identified in another family, strongly supporting the causal role of WDR72 in dRTA. Based on our literature review, WDR72 mutations associated with dRTA have not been previously described. This is the first identification of pathogenic variations in WDR72 as a cause of hereditary dRTA.

Warfarin related nephropathy: the first case report in Thailand

Warfarin is the most prescribed oral anticoagulant. Adverse renal effect from warfarin therapy are uncommon and Thailand is not acquainted. Warfarin-related nephropathy (WRN) is a newly recognized complication of warfarin treatment, especially in patients with chronic kidney disease. The authors hereby report a 56-year-old man who developed gross hematuria and severe acute kidney injury (AKI) necessitating hemodialysis, following supra-therapeutic INR level. Renal pathology revealed extensive intratubular obstruction with red blood cell casts. From the literature, there were only twelve case reports of WRN, which were confirmed by renal histopatology. Renal survival of this condition was unsatisfactory. However, our patient was dialysis-independent after vitamin K treatment and temporary warfarin discontinuation. To the best of our knowledge, this is the first case report of biopsy-proven WRN in Thailand.

Clinico-pathological correlation of severe tubulointerstitial fibrosis in glomerular diseases

BACKGROUND

Renal histopathology is the best method available to assess chronicity ofglomerular diseases. However renal biopsy is an invasive procedure and is available only in medical schools or tertiary-care hospitals in Thailand. Clinical predictors that discriminate the chronicity index of renal pathology may be valuable for the best timing of biopsy. The authors conducted this study to identify the clinical parameters of severe fibrosis in glomerular diseases.

MATERIAL AND METHOD

The authors retrospective analyzed all consecutive patients with glomerular diseases who underwent ultrasound-guided renal biopsy in Siriraj Hospital between 2008 and 2010. The patients were statified according to degree of tubulointerstitial fibrosis (IF) into mild to moderate group (IF < 50%) and severe group (IF ≥ 50%). Data of clinical and radiological parameters which relate to severe fibrosis were obtained. Formula for prediction of advanced IF was also developed by backward stepwise logistic regression analysis. The authors also validated the model by application to the patients who underwent kidney biopsy in our center between 2011 and 2012.

RESULTS

Of a total 682 patients, 169 patients (24.8%) were classified as a severe IF group. In the multivariate model, higher serum creatinine, lower mean length of both kidneys and systolic blood pressure (SBP) of more than 140 mmHg were significantly related to severe IF All three factors were incorporated into apredictive model: e(x)/(1 +e(x)) while x = 1.3 + (0.6 x serum Cr in mg/dl)--(0.4 x mean length of both kidneys in cm)+(0.7 x 1 if SBP ≥ 140 mmHg or 0 if < 140 mmHg). The formula had AUROC of 0.82 and if calculated probability of fibrosis is higher than 0.37, it yields 90% specificity and 44% sensitivity for the prediction ofsevere fibrosis. When applied to 523 patients who underwent renal biopsy in 2011 and 2012, the sensitivity was 65.6% while specificity was 87.8%.

CONCLUSION

High serum creatinine, presence of HT and decreased mean length of both kidneys are important clinical markers to predict renal fibrosis. The model constructed from these factors could be used in clinical practice for appropriate decision making.

Tropical distal renal tubular acidosis: clinical and epidemiological studies in 78 patients

BACKGROUND

Distal renal tubular acidosis (dRTA) caused by mutations of the SLC4A1 gene encoding the erythroid and kidney isoforms of anion exchanger 1 (AE1 or band 3) has a high prevalence in some tropical countries, particularly Thailand, Malaysia, the Philippines and Papua New Guinea (PNG). Here the disease is almost invariably recessive and can result from either homozygous or compound heterozygous SLC4A1 mutations.

METHODS

We have collected and reviewed our own and published data on tropical dRTA to provide a comprehensive series of clinical and epidemiological studies in 78 patients.

RESULTS

Eight responsible SLC4A1 mutations have been described so far, four of them affecting multiple unrelated families. With the exception of the mutation causing South-East Asian ovalocytosis (SAO), none of these mutations has been reported outside the tropics, where dRTA caused by SLC4A1 mutations is much rarer and almost always dominant, resulting from mutations that are quite different from those found in the tropics. SLC4A1 mutations, including those causing dRTA, may cause morphological red cell changes, often with excess haemolysis. In dRTA, these red cell changes are usually clinically recessive and not present in heterozygotes. The high tropical prevalence of dRTA caused by SLC4A1 mutations is currently unexplained.

CONCLUSION

A hypothesis suggesting that changes in red cell metabolism caused by these mutations might protect against malaria is put forward to explain the phenomenon, and a possible mechanism for this effect is proposed.

Efficacy and hemodynamic outcome of prolonged intermittent renal replacement therapy (PIRRT) in critically ill patients: a preliminary report

BACKGROUND

Acute kidney injury (AKI) is frequently part of a multiple-organ dysfunction syndrome presenting in critically ill patients. Prolonged intermittent renal replacement therapy (PIRRT) provides the advantages of both continuous renal replacement therapy (CRRT) in term of hemodynamic stability and the cost-effectiveness of intermittent hemodialysis (IHD). This study aims to study PIRRT in the aspects of efficacy and hemodynamic outcomes.

MATERIAL AND METHOD

The authors present a single-center experience accumulated over 20 months from February 2009 to September 2010 with two PIRRT techniques, called SLEDD and SLEDD-f. Eight-hour treatments were performed daily for three consecutive days. Hemodynamic parameters were recorded at different time points and blood samples were taken for urea and solute clearance before and after treatment.

RESULTS

Sixty critically ill patients with AKI were randomly assigned to undergo PIRRT 33 patients received SLEDD and 27 patients received SLEDD-f. Our results demonstrate significant decrease in BUN, creatinine, serum potassium and phosphate in both PIRRT techniques. Moreover with the use of similar filters and blood flow rates, SLEDD-f was comparable with SLEDD in terms of small solute clearance and detoxification. For hemodynamic outcomes, the authors found that MAP increased after completion of the first session of PIRRT and along the three consecutive days of daily PIRRT, together with the gradual improvement of vasopressor scores.

CONCLUSION

The prolonged intermittent renal replacement therapy (PIRRT) appears to be an outstanding technique for treatment of critically ill patients with AKI and it also seems to have cost effectiveness. Moreover it is suitable to a limited resource region such as Thailand.

Buttonhole technique better than area puncture technique on hemostasis and pain associated with needle cannulation

BACKGROUND

The buttonhole (constant site) arteriovenous fistulae cannulation technique, in which the inserted needle utilizes exactly the same site and the same angle every dialysis session, offers the advantage of an easier cannulation procedure, less pain associated with cannulation, and fewer complications when compared with the traditional method.

OBJECTIVE

To compare buttonhole arteriovenous fistula (AVF) cannulation technique with area puncture method on the effect of hemostasis after needle withdrawal and pain during needle puncture.

MATERIAL AND METHOD

The duration of hemostasis after needle withdrawal and pain during needle puncture of AVF were prospectively recorded in 21 chronic hemodialysis patients at Siriraj Hospital. The data that were collected while using area puncture with sharp needle and while using buttonhole with blunt needle were compared by using Paired t-test.

RESULTS

Compared with area puncture method, the duration of hemostasis after needle withdrawal in patients using buttonhole method was significantly shorter in both arterial (4.19 +/- 1.66 mins vs. 9.12 +/- 2.36 mins, p < 0.0001) and venous site (3.92 +/- 1.37 mins vs. 9.12 +/- 2.36 mins, p < 0.0001). The pain score during needle puncture of AVF in patients using buttonhole method was also significantly less than area puncture method in both arterial (1.20 +/- 0.90 vs. 6.03 +/- 0.90, p < 0.0001) and venous site (1.38 +/- 0.75 vs. 5.88 +/- 0.82, p < 0.0001).

CONCLUSION

Buttonhole AVF puncture method is a useful technique to reduce both the time for hemostasis after needle withdrawal and pain during needle puncture.

Practical guidelines for automated peritoneal dialysis

The development of APD technologies enables physician to customize PD treatment for optimal dialysis. Dialysis dose can be increased with APD alone or in conjunction with daytime dwells. Although there is no strong evidence of the advantage over CAPD, APD is generally recommended for patients having a high peritoneal transport, outflow problems or high intraperitoneal pressure (IPP) and those who depend on caregivers for their dialysis. The benefits of APD over CAPD depends on the problems and treatment results among dialysis centers. Before starting the APD, medical, psychosocial and financial aspects, catheter function, residual renal function (RRF), body surface area and peritoneal transport characteristic must be evaluated. The recommended starting prescription for APD is the dwell volume of 1,500 ml/m2, 2 hours/cycle, and 5 cycles/session, which will provides 10-15 L of total volume and 10 hours per session. The IPP should be monitored and kept below 18 cmH2O. NIPD is accepted for patients with significant RRF. Anuric patients usually require 15-20 L of total fill volume and may need 1-2 day-dwells of 2L icodextrin or hypertonic glucose solutions. Small solute clearances and ultrafiltration depend on the peritoneal catheter function and dialysis schedule. The clinical outcomes and small solute clearances must be monitored and adjusted accordingly to meet the weekly total Kt/V urea > or = 1.7 and in low peritoneal transporters, the weekly total CCr should be > or = 45 L/1.73 m2. The volume status must be normal. To diagnose the peritonitis in NIPD patients, 1 L of PDF should be infused and permitted to dwell for 2 hours before sending for analysis. The differential of white cell count may be more useful than the total cell counts. In Siriraj Hospital, APD patients had 1.5-3 times less peritonitis than CAPD patients and most of our anuric patients can achieve the weekly total Kt/V urea target with 10 L of NIPD.

Nephrotic syndrome in elderly patients: three years experience at Siriraj Hospital

BACKGROUND

The population age is being high and nephotic syndrome is a common renal disease.

OBJECTIVE

To find the etiology and clinical manifestations of nephrotic syndrome in the elderly patients who underwent renal biopsy at Siriraj hospital including management and outcome.

MATERIAL AND METHOD

Retrospective study in 76 nephrotic patients whose age > or =50 years and underwent renal biopsy between 2005-2007.

RESULTS

Seventy six nephrotic patients with age ranged from 50-84 years were analysed. Primary glomerulonephritis diseases were found more than secondary causes (5:2). The two most common glomerulonephritis were membranous GN and focal/segmental glomerulosclerosis. The etiology of common secondary GN was lupus nephtitis 11.84% following by diabetic nephropathy and amyloidosis. The patients received immunosuppressive drugs and complete response was found in 51%, partial response 10.2%, no response was 2% and no immunosuppressive therapy 36.7%. There was 1 patient died of septicaemia.

CONCLUSION

Nephrotic syndrome in the elderly patients were not uncommon. The causes should be identified for prompt management and excellent outcome.

Acute kidney injury in primary nephrotic syndrome: report of nine cases in Siriraj Hospital

Acute kidney injury is a rare but important complication of nephrotic syndrome. We demonstrated here nine patients with nephrotic syndrome and oliguric renal failure in Siriraj Hospital during 2007-2009. Renal biopsy was done in every patient. The results were focal and segmental glomerulosclerosis (FSGS) in three patients, minimal change disease in four patients and collapsing focal segmental glomerulosclerosis in two patients. Seven patients had dramatic response to corticosteroid treatment within a few weeks and had rapid recovery of renal function. The exact mechanism of idiopathic renal failure is not well understood but it might be related to reduction in ultrafiltration coefficient of the glomeruli.

Prothrombin haplotype associated with kidney stone disease in Northeastern Thai patients

OBJECTIVE

To evaluate genetic variations associated with kidney stone disease in Northeastern Thai patients.

METHODS

Altogether, 67 single nucleotide polymorphisms (SNP) distributed within 8 candidate genes, namely TFF1, S100A8, S100A9, S100A12, AMBP, SPP1, UMOD, and F2, which encode stone inhibitor proteins, including trefoil factor 1, calgranulin (A, B, and C), bikunin, osteopontin, tamm-Horsfall protein, and prothrombin, respectively, were initially genotyped in 112 individuals each and in additional subjects to consist of 164 patients and 216 control subjects in total.

RESULTS

We found that minor allele and homozygous genotype frequencies of 8 of 10 SNPs distributed within the F2 gene were significantly higher in the control group than in the patient group. Two F2 haplotypes were found to be dually associated with kidney stone risk, one (TGCCGCCGCG) with increased disease risk and the other (CGTTCCGCTA) with decreased disease risk. However, these 2 haplotypes were associated with the disease risks in only the female, not the male, group.

CONCLUSIONS

The results of our study indicate that genetic variation of F2 is associated with kidney stone risk in Northeastern Thai female patients.

Molecular Approach for Distal Renal Tubular Acidosis Associated AE1 Mutations

The molecular approaches to distal renal tubular acidosis (dRTA) associated AE1 mutations lead us to understand the genetic and pathophysiological aspects of the acidification defects. An unanticipated high value of the urine-blood (U-B) PCO(2) after NaHCO(3) loading observed in a case of dRTA and southeast Asian ovalocytosis (SAO) might be from a mistarget of the AE1 to the luminal membrane of type A intercalated cells. The mutations of the AE1 gene resulted in SAO and also affected renal acidification function. Notwithstanding, after the NH4Cl loading in 20 individuals with SAO, the acidification in the distal nephron was normal. The presence of both SAO and G701D mutations of AE1 gene would explain the abnormal urinary acidification in the patients with the compound heterozogosity. In terms of the effect of the mutations on trafficking of AE1, truncated kidney isoform (kAE1) of wild-type showed a 'dominant-positive effect' in rescuing the recessive mutant kAE1 (S773P or G701D) trafficking to the plasma membrane, in contrast with the dominant mutant kAE1 (R589H) resulting in a 'dominant-negative effect' when heterodimerized with the wild-type kAE1. It is notable that the dominant mutants kAE1 (R901X or G609R) expression in MDCK cells clearly results in aberrant surface expression with some mutant protein appearing at the apical membrane. These might result in net bicarbonate secretion and increasing U-B PCO(2) in the distal nephron. The molecular physiological and genetic approaches have permitted identification of the molecular defects, predominantly in transporter proteins, and should in turn prompt development of novel therapeutic strategies.

The 37-year kidney transplantation experience at Siriraj Hospital

With 37-years of experience, a total of 801 kidney transplantations (59.4% were deceased donors and 40.6% were living donors) performed at Siriraj hospital were reported. The point system parallel to OPTN/UNOS for waitlists was utilized. Most of the recipients of deceased donor kidney transplantations had 3 HLA mismatches. Due to the point allocation system, none of them had 6 HLA mismatches. Extended criteria donor comprised 7.8% of all deceased donors. Mean duration of dialysis prior to deceased donor transplant was 53 +/- 34 months. Delayed graft function (DGF) was found in 54% of deceased donor kidney transplantation and resulted in significantly higher rate of 1 year biopsy-proven acute rejection, longer duration of kidney transplant admission, higher admission cost and lower patient survival compared to those with immediate graft function. Most of living donor kidney transplant recipient had 1 haplotype match. Mean donor age was 35.9 +/- 9.8 years. 95.6% of the recipients were on hemodialysis prior to transplantation. The current standard regimen includes calcineurin inhibitor, Mycophenolic acid and prednisolone. Interleukin-2 receptor monoclonal antibody has been used in the high immunological risk or high risk for DGF recipients that were 50% of the recipients. There was no statistically significant difference in the biopsy-proven acute rejection (BPAR) free survival between deceased and living donor transplantation. Proportion of cases with the diagnosis of acute rejection according to Banff 2007 classification is as follows: 32.4% acute cellular rejection (ACR), 39.4% antibody-mediated rejection (AMR) and 21.1% mixed cellular and antibody-mediated rejection. Seventy two patients, 35 deceased donor and 37 living donor kidney transplant recipients, had biopsy-proven glomerular disease after transplantation which IgA nephropathy is the most common form of glomerulonephritis. Median graft survival was 7.6 and 13.2 years and median patient survival was 12.1 and 15.5 years for recipient of deceased and living donor transplant respectively. The follow up program of living donors was introduced in 2003 and there were not any donors who required renal replacement therapy.

Evidence suggesting a genetic contribution to kidney stone in northeastern Thai population

Genetic factor may play a role in the pathogenesis of kidney stone that is found in the northeastern (NE) Thai population. Herein, we report initial evidence suggesting genetic contribution to the disease in this population. We examined 1,034 subjects including 135 patients with kidney stone, 551 family members, and 348 villagers by radiography of kidney-ureter-bladder (KUB) and other methods, and also analyzed stones removed by surgical operations. One hundred and sixteen of 551 family members (21.05%) and 23 of the 348 villagers (6.61%) were affected with kidney stone. The relative risk (lambda(R)) of the disease among family members was 3.18. Calcium stones (whewellite, dahllite, and weddellite) were observed in about 88% of stones analyzed. Our data indicate familial aggregation of kidney stone in this population supporting that genetic factor should play some role in its pathogenesis. Genetic and genomic studies will be conducted to identify the genes associated with the disease.

Evaluating the clinical course and prognostic factors of posttransplantation immunoglobulin A nephropathy

INTRODUCTION

Previous reports have suggested that posttransplantation immunoglobulin (Ig) A nephropathy displays a relatively benign course, hardly ever affecting graft function. However, more recent studies with longer follow-up have shown that posttransplantation IgA nephropathy may be a significant contributor to graft loss. Additionally, there may be other clinical or pathological factors that affect long-term graft outcome. We retrospectively analyzed 30 kidney transplant recipients with biopsy-proven IgA nephropathy in their allografts to determine the clinical course and prognostic factors in posttransplantation IgA nephropathy. The median duration of follow-up was 36 months (range, 1 month-17 years). The median onset of IgA nephropathy was 33.6 months posttransplantation (range, 5 days-103 months). The most common presentation was an abnormal urine examination (96.6%). Fifteen (50%) displayed microscopic hematuria with proteinuria more than 1 g/d. Fifteen patients (50%) lost their grafts at a median time of 24 months after the onset of disease (range, 1-93 months). Allograft loss was associated with a high serum creatinine level at the time of diagnosis (3.68 +/- 2.23 vs 1.79 +/- 0.34 mg/dL; P = .006), a greater level of proteinuria at the time of diagnosis (2.43 +/- 0.76 vs 1.29 +/- 1.07 g/d; P = .003), and more than 50% extracapillary proliferation (P = .05). Fibrinoid necrosis on allograft pathology impacted 1-year allograft survival (P = .025).

CONCLUSION

Posttransplantation IgA nephropathy worsens allograft outcomes among patients with increased serum creatinine level or significant proteinuria at presentation or significant glomerular inflammation and/or tubulointerstitial damage.

Proteomic analysis of peritoneal dialysate fluid in patients with different types of peritoneal membranes

Efficacy of peritoneal dialysis is determined by solute transport through peritoneal membranes. With the use of the peritoneal equilibration test (PET), peritoneal membranes can be classified as high (H), high average (HA), low average (LA), and low (L) transporters, based on the removal or transport rate of solutes, which are small molecules. Whether there is any difference in macromolecules (i.e., proteins) removed by different types of peritoneal membranes remains unclear. We performed a gel-based differential proteomics study of peritoneal dialysate effluents (PDE) obtained from chronic peritoneal dialysis (CPD) patients with H, HA, LA, and L transport rates (n=5 for each group; total n=20). Quantitative analysis and ANOVA with Tukey's posthoc multiple comparisons revealed five proteins whose abundance in PDE significantly differed among groups. These proteins were successfully identified by matrix-assisted laser desorption ionization quadrupole time-of-flight (MALDI-Q-TOF) mass spectrometry (MS) and tandem mass spectrometry (MS/MS) analyses, including serum albumin in a complex with myristic acid and triiodobenzoic acid, alpha1-antitrypsin, complement component C4A, immunoglobulin kappa light chain, and apolipoprotein A-I. The differences among groups in PDE levels of C4A and immunoglobulin kappa were clearly confirmed in a validation set of the other 24 patients (n=6 for each group) using ELISA. These data may lead to better understanding of the physiology of peritoneal membrane transport in CPD patients. Extending the study to a larger number of patients with subgroup analyses may yield additional information of the peritoneal dialysate proteins in association with dialysis adequacy, residual renal function, nutritional status, and risk of peritoneal infection.

Effect of short-term folate and vitamin B supplementation on blood homocysteine level and carotid artery wall thickness in chronic hemodialysis patients

OBJECTIVE

Hyperhomocysteinemia is an independent risk factor for atherosclerotic vascular disease in chronic hemodialysis patients. This stratified randomized controlled trial was designed to measure the effect of high dose oral vitamin B6, vitamin B12, and folic acid on homocysteine levels, and to evaluate the effect on atherosclerosis as measured by Intima-Media Thickness (IMT) of carotid arteries.

MATERIAL AND METHOD

Fifty-four chronic hemodialysis patients with hyperhomocysteinemia were randomized to receive oral 15 mg folic acid, 50 mg vitamin B6, and 1 mg vitamin B12 daily (treatment group) or oral 5 mg folic acid alone (control group) for 6 months. Homocysteine level and IMT were measured in both groups.

RESULTS

At 6 months, homocysteine levels in the treatment group were significantly reduced from 27.94 +/- 8.54 to 22.71 +/- 3.68 mmol/l (p = 0.009) and were not significantly increased from 26.81 +/- 7.10 to 30.82 +/- 8.76 mmol/l in control group (p = 0.08). Mean difference between both groups was statistically significant (p = 0.002). There was no significant difference of IMT of carotid arteries, however, a tendency that the treatment group would have less thickness was observed (0.69 +/- 0.29 mm and 0.62 +/- 0.16 mm, p = 0.99).

CONCLUSION

Treatment of hyperhomocysteinemia in chronic hemodialysis patients with daily oral 15 mg folic acid, 50 mg vitamin B6, and 1 mg vitamin B12 for 6 months decreases homocysteine levels and tends to reduce IMT of carotid arteries. A long term study for the prevention of atherosclerosis is warranted.

An analysis of 3,555 cases of renal biopsy in Thailand

BACKGROUND

The knowledge of the epidemiology of biopsied renal diseases provides useful information in clinical practice. There are several epidemiologic population-based studies of biopsy-proven nephropathies with detailed clinicopathologic correlations that could be different according to the country analyzed.

OBJECTIVE

To identify the prevalence of primary and secondary glomerular diseases and to study the trend of the pattern changes of the glomerulopathy in Thailand.

MATERIAL AND METHOD

A retrospective study of percutaneous renal biopsies during a 23-year period of 1982 to 2005 was performed. A total of 3,555 consecutive native kidney biopsies in adult patients between 12 and 84 years of age were analyzed for the prevalence and changes in the 5-year interval over the two decades.

RESULTS

From the clinical trial of 3,275 patients, the ratio between primary and secondary glomerular diseases was 2:1 (2154:1121). The most common primary glomerular disease (2154 patients) were IgM nephropathy (n = 986, 45.8%) followed by IgA nephropathy (n = 386, 17.9%); membranous nephropathy (n = 341, 15.8%); diffuse endocapillary proliferative glomerulonephritis (n = 114, 5.3%) and diffuse crescentic glomerulonephritis (n = 71, 3.3%). Lupus nephritis was the most prevalent cause of secondary glomerulonephritis in the present study (n = 992, 88.5%). Examination of the 5-year interval along the study period revealed a significant increase in the prevalence of IgA nephropathy and diabetic nephropathy. Prevalence of focal and segmental glomerulosclerosis rose by five times over the last two decades in contrast to IgM nephropathy, which prevalence is decreasing.

CONCLUSION

There is high prevalence of IgM nephropathy, IgA nephropathy, and lupus nephritis in Thailand which is different from other countries. It could be due to various races and altered environments. The information obtained from these results is an important contribution for the understanding of the prevalence in renal diseases in Thailand. It can be used as the baseline data for making efficient research into the appropriate and beneficial way of management in the future.

Relationship between hyperhomocysteinemia and atherosclerosis in chronic hemodialysis patients

BACKGROUND

Hyperhomocysteinemia is an independent risk factor of coronary artery heart disease (CAHD) and atherosclerosis in a normal population. However, it is still controversial in end-stage kidney disease patients who underwent long-term dialysis. Carotid intima-media thickness (IMT) is the standard non-invasive measurement of atherosclerosis. The aims of the present study were to determine the homocysteine (Hcy) level, and to evaluate its role as a risk factor of atherosclerosis in hemodialysis (HD) patients.

MATERIAL AND METHOD

Clinical data and blood chemistries were assayed in 62 HD patients. Atherosclerosis was defined by clinical presentations of CAHD, cerebrovascular or peripheral vascular diseases, or carotid plaque by ultrasound. IMT was also measured by ultrasound

RESULTS

Plasma Hcy level in HD patients was significantly higher in HD patients than normal controls (28.3 +/- 8.3 vs 9.7 +/- 2.9 micromol/l, p < 0.001). Older age (p < 0.001), male sex (p = 0.05), longer duration of HD (p = 0.05), and higher plasma Hcy level (p = 0.01) correlated with atherosclerosis by univariate analysis, but plasma Hcy did not show significant correlation by multivariable analysis. There was also correlation between IMT and atherosclerosis in HD patients (p < 0.001) but no correlation was observed between plasma Hcy level and lMT.

CONCLUSION

Hyperhomocysteinemia is not an independent factor in the genesis of atherosclerosis in HD patients. Advanced age plays a major role of hyperhomocysteinemia and IMT is a useful marker of atherosclerosis in these patients.

Novel compound heterozygous SLC4A1 mutations in Thai patients with autosomal recessive distal renal tubular acidosis

BACKGROUND

Mutations in the SLC4A1 gene have been found to cause either autosomal dominant (AD) or autosomal recessive (AR) distal renal tubular acidosis (dRTA). The SLC4A1 mutations causing AD dRTA were reported in white patients, whereas those associated with AR dRTA were often found in Southeast Asia. Here, the authors report additional novel SLC4A1 mutations in 3 patients with AR dRTA from 2 unrelated Thai families.

METHODS

The patients and members of their families were clinically studied. Red cell morphology and sulfate influx were examined. The SLC4A1 gene was screened, analyzed, and confirmed for mutations by molecular genetic techniques.

RESULTS

In the first family, the patient had dRTA, rickets, failure to thrive, nephrocalcinosis, and hypokalemic-hyperchloremic metabolic acidosis with a urine pH level of 7.00. He had novel compound heterozygous SLC4A1 G701D/S773P mutations, inherited from clinically normal heterozygous mother and father. In the second family, the patient and his sister had dRTA and Southeast Asian ovalocytosis (SAO) with different clinical severity. The patient had proximal muscle weakness, rickets, nephrocalcinosis, hypokalemia, normal anion gap metabolic acidosis, and urine pH level of 6.80. His sister was asymptomatic but the urine pH level could not be lowered to below 5.50 after a short acid load. Both siblings had compound heterozygous SLC4A1 SAO/R602H mutations.

CONCLUSION

Two novel compound heterozygous SLC4A1 G701D/S773P and SAO/R602H mutations were identified in Thai patients with AR dRTA.

Kidney stone inhibitors in patients with renal stones and endemic renal tubular acidosis in northeast Thailand

Distal renal tubular acidosis (dRTA) is generally associated with hypercalciuria, hypocitraturia, and nephrolithiasis. Our intention was to study glycosaminoglycans (GAGS) and nephrocalcin (NC), two well-known crystal growth inhibitors, in a population with endemic dRTA and nephrolithiasis in northeast (NE) Thailand. We studied 13 patients, six with dRTA and seven with nephrolithiasis with normal or undefined acidification function. Six healthy adults living in the same area as the patients and another six from the Bangkok (BKK) area were used as controls. We measured urinary pH, ammonia, calcium, citrate, magnesium, oxalate, potassium, sodium and uric acid. GAGS were determined by an Alcian blue precipitation method and were qualitated by agarose gel electrophoresis after being isolated using 5% cetyltrimethylammonium bromide at pH 6.0. NC isoforms were isolated as previously described by Nakagawa et al. Citrate was higher in BKK controls ( p<0.04). There was a striking difference among GAGS from BKK when compared with other groups (103.85+/-10.70 vs. 23.52+/-8.11 for dRTA, 22.36+/-14.98 for kidney stone patients and 14.73+/-2.87 mg/ml in controls from the NE region, ( p<0.0001). dRTA and stone-forming patients excrete proportionally more (C+D) than (A+B) NC isoforms ( p<0.05). Also, their NC showed a 100-fold weaker binding capacity of calcium oxalate monohydrate crystals. The ratio of chondroitin sulfate/heparin sulfate in GAGS was approximately 9/1. In addition to the traditional risk factors for nephrolithiasis in dRTA, GAGS and NC might play an important role in the pathogenesis of stone formation in this population.

Anion exchanger 1 mutations associated with distal renal tubular acidosis in the Thai population

We have previously demonstrated that compound heterozygous (SAO/G701D) and homozygous (G701D/G701D) mutations of the anion exchanger 1 (AE1) gene, encoding erythroid and kidney AE1 proteins, cause autosomal recessive distal renal tubular acidosis (AR dRTA) in Thai patients. It is thus of interest to examine the prevalence of these mutations in the Thai population. The SAO and G701D mutations were examined in 844 individuals from north, northeast, central, and south Thailand. Other reported mutations including R602H, DeltaV850, and A858D were also examined in some groups of subjects. The SAO mutation was common in the southern Thai population; its heterozygote frequency was 7/206 and estimated allele frequency 1.70%. However, this mutation was not observed in populations of three other regions of Thailand. In contrast, the G701D mutation was not found in the southern population but was observed in the northern, northeastern, and central populations, with heterozygote frequencies of 1/216, 3/205, and 1/217, and estimated allele frequencies of 0.23%, 0.73%, and 0.23%, respectively. The higher allele frequency of the G701D mutation in the northeastern Thai population corresponds to our previous finding that all Thai patients with AR dRTA attributable to homozygous G701D mutation originate from this population. This suggests that the G701D allele that is observed in this region might arise in northeastern Thailand. The presence of patients with compound heterozygous SAO/G701D in southern Thailand and Malaysia and their apparently absence in northeastern Thailand indicate that the G701D allele may have migrated to the southern peninsular region where SAO is common, resulting in pathogenic allelic interaction.

A de novo R589C mutation of anion exchanger 1 causing distal renal tubular acidosis

Anion exchanger 1 (AE1 or SLC4A1) mutations have been reported to cause distal renal tubular acidosis (dRTA), a disease characterized by impaired acid excretion in the distal nephron. We have recently demonstrated homozygous AE1 G701D mutation as a common molecular defect of autosomal recessive (AR) dRTA in a group of Thai pediatric patients. In the present work, we discovered a de novo heterozygous AE1 R589C mutation, previously documented in inherited autosomal dominant (AD) dRTA. Arginine at this position is conserved in all vertebrate AE proteins indicating its functional importance. Three different mutations at this position (R589C, R589H, and R589S) were all found in AD dRTA and a de novo R589H mutation has previously been recorded. Our report is the second de novo mutation but with a different substituted amino acid. A high prevalence of AE1 R589 mutations and the presence of at least two de novo mutations at this position lead us to propose that codon 589 (CGC) is a "mutational hotspot" of AE1. The mechanism of recurrent mutations probably involves methylation and deamination altering cytosine (C) to thymine (T) in the CpG dinucleotides.

Autosomal recessive distal renal tubular acidosis caused by G701D mutation of anion exchanger 1 gene

Anion exchanger 1 (AE1 or band 3), encoded by the AE1 or SLC4A1 gene, regulates chloride-bicarbonate exchange in erythrocytes and alpha-intercalated cells of the distal nephron. Defects of AE1 at the basolateral membrane of alpha-intercalated cells may result in the failure of hydrogen ion secretion at the apical membrane, leading to distal renal tubular acidosis (dRTA). Abnormalities of the AE1 gene were previously reported to be associated with autosomal dominant dRTA. However, recent studies of Thai dRTA families have shown that mutations in this gene result in autosomal recessive (AR) dRTA, giving rise to the postulation that AE1 gene mutations causing AR dRTA might be found commonly in Thai pediatric patients with dRTA. We performed a study of the AE1 gene using DNA linkage, polymerase chain reaction single-strand conformation polymorphism, restriction endonuclease HpaII digestion, and DNA sequence analyses in eight families involving 12 Thai children with dRTA, shown by abnormal urinary acidification using a short acid-loading test, as well as among their family members. Seven patients with dRTA from five families had the same homozygous missense G701D mutation of the AE1 gene. Their parents or siblings heterozygous for the AE1 G701D mutation were clinically normal and did not have abnormal urinary acidification, although a heterozygous sibling in one family had abnormal urinary acidification. Results of this and previous studies show that a homozygous AE1 G701D mutation causes AR dRTA and is a common molecular defect among Thai pediatric patients with dRTA.

Renal function in adult beta-thalassemia/Hb E disease

Beta-Thalassemia hemoglobin E (beta-thal/Hb E) is the commonest form of hemoglobinopathy in Thailand. Shortened red cell life span, rapid iron turnover and tissue deposition of excess iron are major factors responsible for functional and physiological abnormalities found in various forms of thalassemia. Increased deposition of iron had been found in renal parenchyma of thalassemic patients, but no systematic study of the effect of the deposits on renal functions has been available. The purpose of this study is to describe the functional abnormalities of the kidney in patients with beta-thal/Hb E and provide evidence that increased oxidative stress might be one of the factors responsible for the damage. Urine and serum samples from 95 patients with beta-thal/Hb E were studied comparing with 27 age-matched healthy controls. No difference in the creatinine clearance was observed. beta-thal/Hb E patients excreted significantly more urinary protein (0.8+/-0.5 vs. 0.3+/-0.1 g/day, p < 0.001). Aminoaciduria was found in 16 % of the patients. Analysis of urinary protein by SDS-PAGE electrophoresis and silver staining revealed abnormal pattern of protein with increased small molecular weight (<45 kD) bands. Morning urine analysis showed significant lower urine osmolality (578.3+/-164.6 vs. 762.4+/-169.9 mosm/kg, p < 0.001) in patients. Patients excreted more NAG (N-acetyl beta-D-glucosaminidase, 26.3+/-41.3 vs. 8.4+/-3.9 U/g Cr, p < 0.0001) and beta2-microglobulin, 124.3+/-167 vs. 71+/-65.5 microg/g Cr, p = 0.001. Plasma and urine MDA (malonyldialdehyde) levels were both raised (p < 0.0001). Nine patients were selected for renal acidification study. All were found to be normal, but showed poor response to DDAVP challenge (urine osmolality 533+/-71). This is the first report of renal tubular defects found associated with beta-thal/Hb E disease. The mechanism leading to the damage is not known but it might be related to increased oxidative stress secondary to tissue deposition of iron, as indicated by the raised levels of serum and urine MDA. It is not known whether these functional defects would have any long-term effects on the patients. Further studies are warranted and means of prevention of these defects should urgently be sought.

Autosomal recessive distal renal tubular acidosis associated with Southeast Asian ovalocytosis

BACKGROUND

A defect in the anion exchanger 1 (AE1) of the basolateral membrane of type A intercalated cells in the renal collecting duct may result in a failure to maintain a cell-to-lumen H+ gradient, leading to distal renal tubular acidosis (dRTA). Thus, dRTA may occur in Southeast Asian ovalocytosis (SAO), a common AE1 gene abnormality observed in Southeast Asia and Melanesia. Our study investigated whether or not this renal acidification defect exists in individuals with SAO.

METHODS

Short and three-day NH4Cl loading tests were performed in 20 individuals with SAO and in two subjects, including their families, with both SAO and dRTA. Mutations of AE1 gene in individuals with SAO and members of the two families were also studied.

RESULTS

Renal acidification in the 20 individuals with SAO and in the parents of the two families was normal. However, the two clinically affected individuals with SAO and dRTA had compound heterozygosity of 27 bp deletion in exon 11 and missense mutation G701D resulting from a CGG-->CAG substitution in exon 17 of the AE1 gene. Red cells of the two subjects with dRTA and SAO and the family members with SAO showed an approximate 40% reduction in sulfate influx with normal 4,4'-di-isothiocyanato-stilbene-2,2'-disulfonic acid sensitivity and pH dependence.

CONCLUSION

These findings suggest that compound heterozygosity of abnormal AE1 genes causes autosomal recessive dRTA in SAO.

Distal renal tubular acidosis and high urine carbon dioxide tension in a patient with southeast Asian ovalocytosis

Southeast Asian ovalocytosis (SAO) is the best-documented disease in which mutation in the anion exchanger-1 (AE1) causes decreased anion (chloride [Cl-]/bicarbonate [HCO3-]) transport. Because AE1 is also found in the basolateral membrane of type A intercalated cells of the kidney, distal renal tubular acidosis (dRTA) might develop if the function of AE1 is critical for the net excretion of acid. Studies were performed in a 33-year-old woman with SAO who presented with proximal muscle weakness, hypokalemia (potassium, 2.7 mmol/L), a normal anion gap type of metabolic acidosis (venous plasma pH, 7. 32; bicarbonate, 17 mmol/L; anion gap, 11 mEq/L), and a low rate of ammonium (NH4+) excretion in the face of metabolic acidosis (26 micromol/min). However, the capacity to produce NH4+ did not appear to be low because during a furosemide-induced diuresis, NH4+ excretion increased almost threefold to a near-normal value (75 micromol/L/min). Nevertheless, her minimum urine pH (6.3) did not decrease appreciably with this diuresis. The basis of the renal acidification defect was most likely a low distal H+ secretion rate, the result of an alkalinized type A intercalated cell in the distal nephron. Unexpectedly, when her urine pH increased to 7.7 after sodium bicarbonate administration, her urine minus blood carbon dioxide tension difference (U-B Pco2) was 27 mm Hg. We speculate that the increase in U-B Pco2 might arise from a misdirection of AE1 to the apical membrane of type A intercalated cells.

Prevalence of endemic distal renal tubular acidosis and renal stone in the northeast of Thailand

We have previously reported a large group of patients with endemic distal renal tubular acidosis (EdRTA) admitted to the hospitals in the northeast of Thailand. Since large number of patients were identified in a relatively short period of time, and in an area whose population is homogeneous, we were led to investigate the prevalence of the condition in the area. A survey was conducted in five villages (total population of 3,606) within the northeast of Thailand. 3,013 villagers were examined for urinary citrate concentration and short acid loading test was performed in those with low urinary citrate. 2.8% of the population (2.2-3.4%, 95% confidence interval) failed to lower their urine pH after acid loading; within this group, 0.8% of the population had serum potassium less than or equal to 3.5 mEq/l. In addition a large number of villagers were found to have low urinary citrate concentration and there was concurrent high prevalence of renal stone. The prevalence of EdRTA and renal stone was higher in villagers with poorer socioeconomic status, suggesting that environmental factors play a major role in their pathogenesis. Villagers with acidification defect have 2.4 times the chance of having renal stone and/or nephrocalcinosis. EdRTA is therefore one of the important factors responsible for the high prevalence of renal stone in the area. In conclusion we have confirmed the high prevalence of EdRTA in the northeast of Thailand and provided data showing high prevalence of renal stone and hypocitraturia in the same population.

The spectrum of endemic renal tubular acidosis in the northeast of Thailand

We have previously reported a high prevalence of endemic renal tubular acidosis (EnRTA) in the northeast of Thailand, and our subsequent studies provided evidence that K deficiency exists in the same region. Since tubulointerstitial damage is associated with K deficiency, we postulate that this might be implicated in the pathogenesis of EnRTA and, if so, that a spectrum of tubulointerstitial abnormalities can be anticipated. In this study we evaluated renal acidification ability in 4 patients and in 11 of their relatives. We used a 3-day acid load (NH4Cl 0.1 g/kg/day) followed by 20 mg oral furosemide and monitored the maximal renal concentrating ability using water deprivation and intranasal 1-deamino-D-arginine vasopressin. The results showed that the subjects could be divided into three groups; normal relatives of the patients, those with suspected renal tubular acidosis, and patients with overt EnRTA who had chronic metabolic acidosis and a low rate of excretion of NH4+. The rate of excretion of K was very low (20 +/- 4 mmol/day) in patients with EnRTA and in their relatives with suspected EnRTA. The transtubular K concentration gradient was also very low in their relatives, especially in patients with suspected EnRTA (2.8 +/- 0.2). With a 3-day NH4Cl load, the rate of excretion of NH4+ was very low in patients with EnRTA (32 +/- 9 mmol/day), and the relatives with suspected EnRTA also had a decreased capacity to excrete NH+4 (50 +/- 14 mmol/day). In contrast, the normal relatives excreted 92 +/- 12 mmol of NH+4/day. The patients with EnRTA could lower their urine pH to less than 5.5 after the acid loading (6.2 +/- 0.3). After furosemide (20 mg), the NH4+ excretion in the patients with EnRTA was lower than in the normal relatives. Moreover, the minimum urine pH in patients with EnRTA did not fall (6.1 +/- 0.2), but there was a fall to 4.8 +/- 0.1 in the patients with suspected EnRTA after furosemide treatment. In conclusion, there was a spectrum of tubulointerstitial abnormalities ranging from suspected to overt distal RTA in a geographic area known to have a high prevalence of K deficiency. K deficiency might be the important pathogenetic factor of EnRTA in the northeast of Thailand.

Lupus nephritis in Thailand: clinicopathologic findings and outcome in 569 patients

The prognosis of lupus nephritis patients in Thailand has been reported to be poorer than that in Western countries since 1978. After a great evolution in management, we re-evaluate the long-term outcome in patients who were treated and followed up at Siriraj Hospital in Bangkok from 1984 to 1991. Clinical and pathologic records were collected from 569 patients (515 females and 54 men) who were followed up for a mean period of 38.7 +/- 34.6 months. The mean age was 28 +/- 10 years and the median duration of symptoms prior to admission was 7 months. Hypertension was diagnosed in 32.4% of patients and 41.3% had serum creatinine greater than 1.5 mg/dL. Nephrotic-range proteinuria was found in 43.6% of patients and creatinine clearance less than 50 mL/min was found in 58.0%. Of the 314 patients who underwent renal biopsy, the most common histologic finding was diffuse proliferative glomerulonephritis (61.5%). The overall probability of survival was 76.5% at 60 and 90 months after diagnosis. Initial presence of hypertension, renal insufficiency (creatinine clearance < 25 mL/min), and World Health Organization histology class IV and III in the biopsied patients were the three independent factors significantly associated with lower survival probability. Neither gender nor amount of proteinuria was the predictive factor for poor outcome. During the follow-up period, 89 patients died and two patients entered a chronic dialysis program. The two leading causes of death were infection (50.5%) and uremia (28.6%).(ABSTRACT TRUNCATED AT 250 WORDS)

Lupus nephritis in males: 8-year experience at Siriraj Hospital

During 1984 to 1991, 54 out of 569 lupus nephritis patients at Siriraj Hospital were male (F:M sex ratio = 10:1). Mean age of the males was 29.8 +/- 14.6 years, range 12 to 69. The three most common extrarenal manifestations were anemia, cutaneous, and musculoskeletal involvement (74.5, 51.1, and 43.9%, respectively). The major renal manifestations were edema (75.9%) with heavy proteinuria over 3.5 g/day in 62.2% and nephrotic/nephritic findings in 51.9% of cases. Hypertension was found in 35.2%. Mean serum creatinine was 2.0 +/- 1.4 mg/dl while 60.5% of cases had creatinine clearance below 50 ml/minute. Mean serum albumin was 2.6 +/- 0.8 g/dl, cholesterol 262.8 +/- 129.5 and triglycerides 343.2 +/- 244.6 mg/dl. Interestingly, hypercholesterolemia (> 250 mg/dl) was found only in 44.8% of cases with nephrotic syndrome. Antinuclear antibody was demonstrated in 91.5%, anti-dDNA antibody in 64.4% and LE cells in 40.4% of cases. Renal biopsy was done in 45 patients and 30 cases (66.7%) were classified as diffuse proliferative nephritis (WHO type IV), 15.6% of type II, 6.7% each of type III and V, with the rest of type V plus IV (4.4%). Tubulointerstitial inflammation was found in 77.3% of cases. During the follow-up period (42 +/- 35.8 months), 6 patients died. The cause of death were uremia in 3, infection in 2, and cardiac failure in 1. By life-table analysis, the probabilities of survival for 1 and 5 years were 89.5 and 80.6%, respectively. In comparison between sexes, except for a higher amount of urinary protein excretion (4.5 +/- 3.1 vs 3.5 +/- 3.0 g/day, p < 0.05), there were no statistically significant differences in clinical and pathological parameters, and probability of survival.

Does saline "correct" the abnormal mass balance in metabolic alkalosis associated with chloride depletion in the rat?

An elevated plasma pH and bicarbonate are the clinical hallmarks of metabolic alkalosis. Nevertheless, to fully define its pathophysiology, one needs a quantitative interpretation of events in 3 areas - the ECF, ICF, and urine. Accordingly, our purpose was to study mass balance in Cl--depletion metabolic alkalosis with normal initial balance for Na+ and K+. In the 20 h following the "exchange" of Cl- (loss, 2455 mumol) and HCO(3-) (gain, 2455 mumol), only 334 mumol HCO(3-) remained in the ECF and 337 mumol were excreted. The remaining 1784 mumol disappeared primarily via titration because 3051 mueq of endogenous anions were produced and excreted largely with K+. Accordingly, metabolic alkalosis was associated with a deficit rather than a surplus of HCO(3-). To reflect the shift of H+ into cells driven by the exit of K+, the cumulative deficit of Cl- was replaced as KCl or NaCl. The fall in plasma [HCO(3-)] was larger in the KCl group (13.2 vs. 9.4 mmol/L); it was largely due to H+ exit from cells; in contrast, disappearance of HCO(3-) from the ECF was due to new endogenous acid production in the NaCl group. Thus, there was an overall deficit of HCO(3-) in metabolic alkalosis associated with KCl depletion (extracellular alkalosis and intracellular acidosis); processes in the ICF were not corrected by NaCl.

A method to evaluate renal ammoniagenesis in vivo

A reduced rate of excretion of ammonium (NH4+) can be due to either a low rate of production and/or a low transfer of NH4+ to the urine. At present, there is no way to obtain a measure of the rate of production of NH4+ in vivo without invasive techniques. Hence, our purpose was to develop a non-invasive test to reflect this rate in vivo. Conditions were selected so that there would be a wide range in the rate of production of NH4+ in the kidney. Initial experiments were performed in dogs because both the rate of production and excretion of NH4+ could be measured directly. The rate of excretion of NH4+ in normal dogs on their usual diet varied over a wide range and was not directly related to its rate of production. Nevertheless, 59% of the NH4+ produced was excreted when the pH of urine was < 6 or when the rate of flow of urine was high (after administering a loop diuretic). To produce a urine with a low pH and high flow rate in humans, a loop diuretic (20 mg of furosemide) and a mineralocorticoid (200 micrograms of fludrocortisone) were given. The pH of urine fell to 5.1 and the rate of urine flow rose to 8 ml/min; the rate of excretion of NH4+ rose from 21 to 33 mumol/min when the urine flow rate rose.(ABSTRACT TRUNCATED AT 250 WORDS)

Kaliuretic response to aldosterone: influence of the content of potassium in the diet

The excretion of potassium (K+) decreased by 50% (30 v 63 mEq/d, P < .01) when subjects consumed a diet that was low in K+ for 3 days. Although part of this conservation of K+ was achieved in part by suppressing the release of aldosterone, nevertheless providing exogenous mineralocorticoids did not lead to a large kaliuresis when there was a modest degree of K+ depletion. Accordingly, the purpose of this study was to evaluate possible mechanisms for this antikaliuretic response to mineralocorticoids. The renal handling of K+ was examined by independent analysis of the two factors that influence its excretion, the driving force to secrete K+ and the urine volume. This driving force is reflected in a noninvasive fashion by the transtubular [K+] gradient (TTKG). Stimuli to increase the rate of excretion of K+ in subjects on a normal and a low-K+ diet included the administration of 200 micrograms fludrocortisone (9 alpha F), the induction of a high urine flow rate (9 alpha F+furosemide), the induction of bicarbonaturia (9 alpha F+acetazolamide), and the excretion of Cl(-)-poor urine (< 15 mEq/L). On the low-K+ diet, the peak value for the TTKG 3 to 4 hours after 9 alpha F was less than half that while on the normal diet (6.4 v 14, P < 0.01). In contrast, the TTKG was not significantly different on either diet when there was bicarbonaturia or the excretion of a Cl(-)-poor urine (18 v 17 and 17 v 16, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Might distal renal tubular acidosis be a proximal tubular cell disorder?

Incomplete renal tubular acidosis (RTA) and overt distal RTA may be different stages of the same underlying pathophysiology in certain individuals. The rationale that draws these conditions together is the relatively alkaline pH of the urine, hypocitraturia, and a possible familial association. The rate of excretion of ammonium (NH4+), on the other hand, suggests that these conditions stem from fundamentally different lesions. To explain this difference, we suggest that two possible disorders may result in the evolution from incomplete RTA to overt distal RTA. One subgroup could have gradient-limited distal RTA, while the other subgroup may have a lower pH of the intracellular fluid of the proximal convoluted tubular epithelium. Indices of proximal intracellular pH (rates of excretion of NH4+, NH3, and citrate) were culled from the literature spanning the years 1959 to 1991 on patients with incomplete RTA and overt distal RTA. Three points emerge: (1) the rate of excretion of NH4+ was lower in patients with overt distal RTA than in normals following an acute acid load (23 +/- 1 v 49 +/- 3 mumol/min); (2) the concentration of NH3 in the urine was almost 25-fold higher in incomplete RTA than in normals (69 +/- 14 v 3 +/- 0.4 nmol/min); and (3) in incomplete RTA, the pH of the urine fell to very low values (4.9 +/- 0.1) when high urine flows were induced with furosemide. The low pH of the urine would therefore suggest that many of these patients do not gradient-limited distal RTA, but more likely have proximal renal epithelial cell acidosis. We hypothesize that this high rate of excretion of NH4+ and low rate of excretion of citrate in the absence of acidosis or hypokalemia is consistent with proximal cell acidosis. To explain a transition from incomplete RTA to overt distal RTA, we speculate that toxicity of high concentrations of NH3 in the medullary interstitium as well as nephrolithiasis and nephrocalcinosis due to low urinary citrate and possibly an alkaline medullary interstitium may lead to damage of structures in this region.

Quantitative role of the intracellular bicarbonate buffer system in response to an acute acid load

Our purpose was to quantitate the proportion of H+ removed by the bicarbonate buffer system (BBS) when a modest load of H+ was infused acutely. In addition, the quantitative impact of hyperventilation on the BBS in the extracellular fluid (ECF) and other compartments in this setting was assessed. Three groups of rats (399 +/- 3 g) were anesthetized and connected to a respirator to control their arterial PCO2 and to collect expired air. Metabolic acidosis (pH 7.26 +/- 0.01, bicarbonate 18 +/- 1 mM) was induced by infusion of HCl (0.15 M, 4 mmol/kg) over 60 min, and expired air was collected for two 20-min periods beginning 75 and 105 min after the start of the infusion of HCl in each group. Each rat served as its own control for the rate of production of CO2 from metabolism. The first two groups were time controls. Their arterial PCO2 was constant at either ambient (50 mmHg) or hyperventilation levels (30 mmHg) during both collections (n = 5 each). In the experimental group (n = 5), the PCO2 was decreased from 40 to 27 mmHg during the second collection. The rate of production of CO2 from metabolism did not rise in the second collection in the time control experiments (change = -13.4 +/- 1.7 and -1.4 +/- 2.5 mumol/min, respectively), whereas more CO2 was collected during the second period in the experimental group (change = 42 +/- 9 mumol/min, P = 0.02).(ABSTRACT TRUNCATED AT 250 WORDS)

Should the urine PCO2 or the rate of excretion of ammonium be the gold standard to diagnose distal renal tubular acidosis?

A high rate of excretion of ammonium (NH4+) during chronic metabolic acidosis should rule out the diagnosis of distal renal tubular acidosis (RTA). Bearing this in mind, the purpose of this report is to demonstrate that a low urine minus blood PCO2 difference in alkaline urine (U-B PCO2) is a less reliable indicator of the diagnosis of distal RTA. The patient who is the subject of this report sniffs glue on a chronic, but intermittent basis. He presented with metabolic acidosis (pH 7.20; bicarbonate, 10 mmol/L) and an anion gap in plasma of 20 mEq/L. The urine anion gap (-14 mEq/L) and osmolal gap (185 mmol/L [mOsm/kg] H2O) suggested that there was a high, rather than a low, rate of excretion of NH4+. This was confirmed by direct measurement of NH4+ in the urine (101 mumol/min). The high rate of excretion of NH4+ suggested that the metabolic acidosis was due, in large part, to an abnormally high rate of production of acid (hippuric acid, because the rate of excretion of hippurate was 76 mumol/min). The U-B PCO2 was low (10 mm Hg) on the second hospital day, after the acidosis was corrected. Potential reasons for the discrepancy between the high rate of excretion of NH4+ and the low U-B PCO2 are discussed.

Pathogenesis of sudden unexplained nocturnal death (lai tai) and endemic distal renal tubular acidosis

Sudden unexplained nocturnal death (SUND), a disorder of unknown cause that occurs in otherwise healthy young adults, mostly male, during their sleep, is prevalent in the north-east region of Thailand, where it has been known for generations as lai tai. It occurs in the same population and area where hypokalaemic periodic paralysis (HPP), endemic distal renal tubular acidosis (EdRTA), and renal stones are also endemic. SUND has occurred in families of patients with EdRTA, and HPP can present as sudden onset of muscle parlysis with potentially lethal cardiac arrhythmias and respiratory failure from severe hypokalaemia occurring in the middle of the night. Surveys in which serum and urinary potassium have been measured indicate a deficiency of the electrolyte in the population. Potassium deficiency is probably the prime factor responsible for SUND and HPP. Low urinary citrate concentrations and the high prevalence of acidification defects in the population indicate that potassium deficiency is also responsible for the prevalence of EdRTA and for renal stones.

Modulation of the secretion of potassium by accompanying anions in humans

In animals, secretion of potassium (K) in the cortical collecting duct (CCD) is modulated by the properties of the accompanying anion. In humans, results are inconclusive as previous studies have not differentiated between a kaliuresis due to a rise in the concentration of K from one due to an increase in the volume of urine. Our purpose was to study the effects of chloride (Cl) and bicarbonate on the secretion of K in the CCD in humans using the transtubular K concentration gradient (TTKG), a semi-quantitative index of secretion of K in the terminal CCD. After control blood and urine samples were obtained, all subjects ingested 0.2 mg fludrocortisone to ensure that mineralocorticoids were not limiting the secretion of K. The anionic composition of the urine was varied using three protocols: Normal subjects (N = 11) ingested cystine and methionine to induce sulfaturia; nine subjects with a contracted ECF volume (to lower the concentration of Cl in the urine) were also studied during sulfaturia following the ingestion of cystine and methionine; 13 normovolemic subjects were studied during bicarbonaturia following the ingestion of acetazolamide. When the concentration of Cl in the urine was greater than 15 mmol/liter, sulfate had no effect on the TTKG. With lower concentrations of Cl in the urine, the TTKG rose 1.5-fold. The TTKG rose 1.8-fold in the presence of bicarbonaturia despite concentrations of Cl in the urine that were greater than 15 mmol/liter, suggesting that bicarbonate has additional effects on this K secretory process. At comparable concentrations of sulfate and bicarbonate in the urine, the TTKG was increased only with bicarbonaturia.(ABSTRACT TRUNCATED AT 250 WORDS)

Glue-sniffing and distal renal tubular acidosis: sticking to the facts

An index case is presented to introduce the subject of the acid-base and electrolyte abnormalities resulting from toluene abuse. These include metabolic acidosis associated with a normal anion gap and excessive loss of sodium and potassium in the urine. The major question addressed is, what is the basis for the metabolic acidosis? Overproduction of hippuric acid resulting from the metabolism of toluene plays a more important role in the genesis of the metabolic acidosis than was previously believed. This conclusion is supported by the observation that the rate of excretion of ammonium was not low during metabolic acidosis in six of eight patients, suggesting that distal renal tubular acidosis was not an important acid-base abnormality in most cases where ammonium was measured. The excretion of hippurate in the urine unmatched by ammonium also mandates an enhanced rate of excretion of the cations, sodium and potassium. The loss of sodium causes extracellular fluid volume contraction and a fall in the glomerular filtration rate, which may transform the normal anion gap type of metabolic acidosis into one with a high anion gap (accumulation of hippurate and other anions). Continuing loss of potassium in the urine leads to hypokalemia. An understanding of the metabolism of toluene provides the basis for the unusual biochemical abnormalities seen with abuse of this solvent.

Urinary constituents in an endemic area of stones and renal tubular acidosis in northeastern Thailand

Nephrolithiasis and endemic renal distal tubular acidosis are common in northeastern Thailand. The etiology is still unknown. It is generally accepted that urine electrolytes influence the capacity of urine to inhibit or promote renal and also bladder stones. The purpose of this study was to analyse the composition of the urine in the indigenous population in the northeast area and compare their values with data obtained from a group of age matched adults, living in Bangkok. Twenty-four hour urine samples from 23 normal adult villagers from six villages within the province of Khon Kaen and 34 normal adults living in Bangkok were collected, and the daily excretion of creatinine, uric acid, calcium and inorganic phosphate, sodium, potassium, chloride, magnesium and oxalate were assayed. Daily urinary sodium, potassium, chloride and phosphate of the villagers were significantly lower than those of Bangkokians. No difference in the urinary excretion of calcium, magnesium, uric acid, oxalate and creatinine was found. The Na/Ca, and Ca/PO4 ratios of villagers were significantly lower than those of the Bangkok subjects. The villagers excreted significantly lower amounts of Na in the face of relatively higher urinary Ca. The above data, combined with our previous study showing the low values of urinary citrate in the villagers in the same areas, strongly indicate that the indigeneous population is at high risk in developing urolithiasis. The causes for these electrolyte abnormalities are still unknown. Low contents of the major electrolytes in their diets might play an important role. Low phosphate output indicates low protein diets.(ABSTRACT TRUNCATED AT 250 WORDS)

Endemic primary distal renal tubular acidosis in Thailand

Within a period of 3 years, 103 patients with primary type I distal renal tubular acidosis were reported from two hospitals in the northeast of Thailand, with cases peaking in the summer. The patients' age ranged from 18 to 76 with a mean and mode of 39 and 47 years, respectively. The female to male ratio was 3.3:1. All patients presented with generalized muscle weakness and bone pain and nocturia were frequent manifestations. Hypokalaemia and hyperchloraemic metabolic acidosis were constant findings and were more pronounced in patients with roentgenographic evidence of nephrocalcinosis and osteomalacia. Urinary citrate was extremely low in most of the patients. Nephrocalcinosis and/or renal stones were present in 27.2% of the patients and osteomalacia was found in 23.3%. All patients were Lao-Thai. This is the first report of a large group of patients with distal renal tubular acidosis, endemic within a particular geographical region.