Achra Sumboonnanonda

Novel AE1 mutations in recessive distal renal tubular acidosis. Loss-of-function is rescued by glycophorin A.

The AE1 gene encodes band 3 Cl-/HCO3- exchangers that are expressed both in the erythrocyte and in the acid-secreting, type A intercalated cells of the kidney. Kidney AE1 contributes to urinary acidification by providing the major exit route for HCO3- across the basolateral membrane. Several AE1 mutations cosegregate with dominantly transmitted nonsyndromic renal tubular acidosis (dRTA). However, the modest degree of in vitro hypofunction exhibited by these dRTA-associated mutations fails to explain the disease phenotype in light of the normal urinary acidification associated with the complete loss-of-function exhibited by AE1 mutations linked to dominant spherocytosis. We report here novel AE1 mutations linked to a recessive syndrome of dRTA and hemolytic anemia in which red cell anion transport is normal. Both affected individuals were triply homozygous for two benign mutations M31T and K56E and for the loss-of-function mutation, G701D. AE1 G701D loss-of-function was accompanied by impaired trafficking to the Xenopus oocyte surface. Coexpression with AE1 G701D of the erythroid AE1 chaperonin, glycophorin A, rescued both AE1-mediated Cl- transport and AE1 surface expression in oocytes. The genetic and functional data both suggest that the homozygous AE1 G701D mutation causes recessively transmitted dRTA in this kindred with apparently normal erythroid anion transport.

Renal tubular function in β-thalassemia

Abstract. Studies of the renal involvement in thalassemic syndromes have been varied and few. This study was designed to define the renal abnormalities associated with β-thalassemia and to correlate the renal findings with clinical parameters. One hundred and four β-thalassemic children with various disease severity were studied. The patients were divided into three groups: 48 with severe anemia [hematocrit (Hct) <25%], 31 on a hypertransfusion program and desferrioxamine treatment, and 25 with moderate anemia (Hct >25%). The results were compared with 15 normal children. Significantly higher levels of proteinuria and low molecular weight proteinuria were found in all patients compared with normal children. Aminoaciduria was detected in one-third of patients. Thalassemic patients had significantly lower morning urine osmolarity, higher urine N-acetyl-β-D-glucoseminidase and malondialdehyde (MDA, an indicator of lipid peroxidation). Patients with severe anemia had significantly higher low-molecular weight proteinuria and MDA, and lower urine osmolarity than those with moderate anemia. Our data confirmed the high frequency of renal abnormalities in β-thalassemia patients and indicated some degree of proximal tubular dysfunction. Severity of the abnormalities correlated with the degree of anemia and were least severe in patients on hypertransfusion and desferrioxamine therapy. This suggested that the damage might be caused by anemia and increased oxidation induced by excess iron deposits.

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.

A novel mutation in the beta-subunit of the epithelial sodium channel gene (SCNN1B) in a Thai family with Liddle's syndrome.

Liddles syndrome is a rare form of autosomal dominant hypertension with early penetrance and cardiovascular sequelae. It is caused by missense or frameshift mutations in the epithelial sodium channel (ENaC) gene resulting in excessive salt and water resorption from the distal nephron, volume expansion, and suppression of plasma renin activity and serum aldosterone secretion. Treatment with an antagonist of the amiloride-sensitive ENaC, amiloride or triamterine, can correct hypertension and biochemical abnormalities in Liddles syndrome by closing the sodium channels. Missense and truncation mutations at the C-terminus of the ENaC gene have been found in two of the three genes encoding beta- and gamma-subunits of ENaC. We report here a Thai family with Liddles syndrome caused by a novel P615H missense mutation in the proline-rich domain of the SCNN1B gene coding for the beta-subunit of ENaC. This mutation occurs within the conserved proline-rich (PY) motif at the C-terminal end and emphasizes the critical role of this motif in ENaC internalization. The presence of severe hypertension and/or a suggestive family history of hypertension with or without hypokalemia in young children should always raise a suspicion of Liddles syndrome.

RENAL FAILURE IN TWO PATIENTS WITH WOLFRAM SYNDROME

We describe a Thai family with three children, two of whom presented with Wolfram syndrome, which is a rare syndrome characterised by diabetes insipidus, diabetes mellitus, optic atrophy, deafness and urinary tract dilatation. A girl and her younger brother had insulin-dependent diabetes mellitus at 11 years old with early onset of renal impairment, proteinuria and hypertension. Urinary tract dilatation was demonstrated in both patients. Kidney biopsies were compatible with diabetic nephropathy. Both children also had bilateral sensorineural hearing loss. Optic atrophy with severe loss of vision was detected in the girl and bilateral cataract in her brother. Both patients were HLA DR2 positive. At 16 years old, her creatinine clearance was 16 ml/min/1.73 m2. Her brothers creatinine clearance was 25 ml/min/1.73 m2 at 13 years old. We conclude that renal function should be evaluated in patients with Wolfram syndrome and the cause of renal failure in these patients may be rapid and severe diabetic nephropathy.

Long-term outcome in pediatric renal tumor survivors: experience of a single center.

Medical records of 30 children with renal tumor diagnosed at Siriraj Hospital during 1996 to 2007 were reviewed. Mean age at diagnosis was 36 months; male to female ratio was 1.7:1. Clinical manifestations included abdominal mass (96.7%), hypertension (40.0%), abdominal pain (36.7%), hematuria (26.7%), postrenal obstruction (16.7%), and proteinuria (13.3%). Eight patients had Denys-Drash malformations, WAGR, Dandy-Walker malformation, or genitourinary anomalies. Twenty-seven patients (90%) had Wilms tumor. Sixteen patients were stage 3 or more at diagnosis. Rhabdoid tumor was found in 3 patients. All patients received chemotherapy, 13 patients also received radiation therapy. Acute complications included febrile neutropenia (44.4%), hypokalemia (37.0%), hyponatremia (29.6%), Fanconi syndrome (11.1%), urinary tract Infection (10.0%), and acute renal failure (7.4%). Mean follow-up time was 57.2 months. Ten patients died from progressive disease. Five-year patient survival was 69.7%. Two patients had chronic kidney disease. One of these had Denys-Drash malformations. Both patients received ifosfamide-carboplatin-etoposide protocol and abdominal radiation. Antihypertensive medications were needed in 9 patients for a mean duration of 164 days. None had persistent proteinuria or hematuria. No difference was found among mean estimated glomerular filtration rate at diagnosis, 1 year after treatment, and at last follow-up. Long-term follow-up, especially renal function, is recommended.

Renal outcome and risk factors for end‐stage renal disease in pediatric rapidly progressive glomerulonephritis

Rapidly progressive glomerulonephritis (RPGN), defined as acute nephritic syndrome with dramatic loss of renal function within a few months, is associated with crescentic glomerulonephritis (CresGN), which requires ≥50% crescents on pathology. The disease characteristics and renal outcome in children with RPGN, however, will differ according to the percentage of crescents.

Immune-mediated hemolytic anemia in pediatric renal transplantation.

Abstract:  The aim of the study was to demonstrate clinical course of the first reported cases of PLS in pediatric kidney transplantation and therapeutic outcome for such condition using a combination of high‐dose corticosteroid and tacrolimus. We report a single case (a nine‐year‐old Thai boy) with end‐stage kidney disease secondary to obstructive uropathy developed immune‐mediated hemolytic anemia from the PLS at second week after a pre‐emptive living‐related kidney transplantation. The alloimmune hemolysis was a result of anti‐B antibodies, derived from blood group O‐donor lymphocytes. Using a combination of high‐dose corticosteroid and a substitution of cyclosporin with tacrolimus, there was no further hemolysis although the anti‐B antibodies remained detectable until the eighth week post‐transplantation. An impairment of the graft function because of hemoglobinuria was resolved after the hemolysis was stopped. The alloimmune hemolysis caused by PLS in pediatric kidney transplantation could be controlled with a combination of high‐dose corticosteroid and tacrolimus.

Combined renin angiotensin blockade in childhood steroid-resistant nephrotic syndrome.

Background:  Reduced proteinuria results in delayed deterioration of renal function and remission of proteinuria predicts a good long‐term prognosis in steroid‐resistant nephrotic syndrome (SRNS). The aim of this study was to analyze the effects of the combined angiotensin‐converting enzyme inhibitor and angiotensin II receptor blocker in reducing proteinuria in SRNS.