Primary hyperoxaluria type 1 in The Netherlands: prevalence and outcome

The effect of acidification and oxalate concentration on urine calcium measurements in EQAS materials and patient samples

BACKGROUND

An increase in urine calcium compared to the consensus value was observed in some urine samples of the Dutch External Quality Assessment Scheme (EQAS). It appeared that the increase was due to the addition of oxalate by the EQAS organizers and preanalytical acidification of the samples by some of the participants. Because of this observation, the effect of urine acidification on urine calcium level in EQAS and patient samples with added oxalate was investigated.

METHODS

Twenty-four EQAS urine samples and 20 patient urine samples were subject to recovery measurements of urine calcium before and after addition of sodium oxalate and acidification.

RESULTS

Differences in urine calcium between acidified and non-acidified samples up to 30.9% have been observed in EQAS samples with added oxalate. Patient samples show differences up to 80%. Differences between acidified and non-acidified samples are minimal for low calcium oxalate levels but increase with higher levels. Samples without added oxalate show equal urine calcium results between acidified and non-acidified samples.

CONCLUSIONS

Urine calcium results are decreased in non-acidified samples with an excess of oxalate. In case of hyperoxaluria, acidification of patient urine collections and EQAS samples is recommended for correct urine calcium values.

Primary hyperoxaluria

Primary hyperoxalurias (PH) are inborn errors in the metabolism of glyoxylate and oxalate. PH type 1, the most common form, is an autosomal recessive disorder caused by a deficiency of the liver-specific enzyme alanine, glyoxylate aminotransferase (AGT) resulting in overproduction and excessive urinary excretion of oxalate. Recurrent urolithiasis and nephrocalcinosis are the hallmarks of the disease. As glomerular filtration rate decreases due to progressive renal damage, oxalate accumulates leading to systemic oxalosis. Diagnosis is often delayed and is based on clinical and sonographic findings, urinary oxalate assessment, DNA analysis, and, if necessary, direct AGT activity measurement in liver biopsy tissue. Early initiation of conservative treatment, including high fluid intake, inhibitors of calcium oxalate crystallization, and pyridoxine in responsive cases, can help to maintain renal function in compliant subjects. In end-stage renal disease patients, the best outcomes have been achieved with combined liver-kidney transplantation which corrects the enzyme defect.

Selected AGXT gene mutations analysis provides a genetic diagnosis in 28% of Tunisian patients with primary hyperoxaluria

Background

Primary hyperoxaluria type I (PH1) is a rare genetic disorder characterized by allelic and clinical heterogeneity. Four mutations (G170R, 33_34insC, I244T and F152I) account for more than 50% of PH1 alleles and form the basis for diagnostic genetic screening for PH1. We aimed to analyze the prevalence of these specific mutations causing PH1, and to provide an accurate tool for diagnosis of presymptomatic patients as well as for prenatal diagnosis in the affected families.

Methods

Polymerase chain reaction/Restriction Fragment Length Polymorphism, were used to detect the four mutations in the AGXT gene in DNA samples from 57 patients belonging to 40 families.

Results

Two mutations causing PH1 were detected in 24 patients (42.1%), with a predominance of the I244T mutation (68% of patients) and 33_34insC (in the remaining 32%). In 92% of cases, mutated alleles were in homozygous state.

The presented clinical features were similar for the two mutations. The age of onset was heterogeneous with a higher frequency of the pediatric age. In 58.3% of cases, the presentation corresponded to advanced renal disease which occurred early (< 5 years) in the two mutations. In adolescents, only the I244T mutation was detected (41.1%). I244T and 33_34insC mutations were observed in adult patients, with 17.6% and 12.5% respectively.

Conclusion

Limited mutation analysis can provide a useful first line investigation for PH1. I244T and 33_34insC presented 28.2% of identified mutations causing disease in our cohort. This identification could provide an accurate tool for prenatal diagnosis in the affected families, for genetic counselling and for detection of presymptomatic individuals.

Efficacy and safety of Oxalobacter formigenes to reduce urinary oxalate in primary hyperoxaluria

BACKGROUND

Primary hyperoxaluria (PH) is a rare genetic disease, in which high urinary oxalate (Uox) cause recurrent kidney stones and/or progressive nephrocalcinosis, often followed by early end-stage renal disease, as well as extremely high plasma oxalate, systemic oxalosis and premature death. Oxalobacter formigenes, an anaerobic oxalate degrading bacterium, naturally colonizes the colon of most humans. Orally administered O. formigenes (Oxabact) was found to significantly reduce urine and plasma oxalate. We aimed to evaluate its effect and safety in a randomized, double-blind, placebo-controlled multicenter study.

METHODS

Oral Oxabact was given to PH patients (>5 years old, Uox > 1.0 mmol/1.73 m(2)/day, glomerular filtration rate (GFR) > 50 mL/min) at nine PH referral sites worldwide. Primary endpoint was the change from baseline in Uox (mmol/1.73 m(2)/day) after 24 weeks of treatment (>20% reduction).

RESULTS

Of the 43 subjects randomized, 42 patients received either placebo (23 subjects) or Oxabact (19 subjects). The change in Uox was <20% and not different between groups (P = 0.616). Ad hoc analysis was performed in 37 patients compliant with medication and urine processing. Change in Uox was -19% in subjects given Oxabact and -10% in placebo, (P = 0.288), but -21 and -7% with Uox expressed as molar creatinine ratio (Ox:Cr, mmol/mol, P = 0.06). Reduction of Ox:Cr was more obvious for patients with higher baseline values (>160 mmol/mol, Oxabact -28%, placebo -6%; P < 0.082). No serious adverse events were reported.

CONCLUSION

Oxabact was safe and well tolerated. However, as no significant change in Uox was seen, further studies to evaluate the efficacy of Oxabact treatment are needed.

Transplantation outcomes in primary hyperoxaluria

Optimal transplantation strategies are uncertain in primary hyperoxaluria (PH) due to potential for recurrent oxalosis. Outcomes of different transplantation approaches were compared using life-table methods to determine kidney graft survival among 203 patients in the International Primary Hyperoxaluria Registry. From 1976-2009, 84 kidney alone (K) and combined kidney and liver (K + L) transplants were performed in 58 patients. Among 58 first kidney transplants (32 K, 26 K + L), 1-, 3- and 5-year kidney graft survival was 82%, 68% and 49%. Renal graft loss occurred in 26 first transplants due to oxalosis in ten, chronic allograft nephropathy in six, rejection in five and other causes in five. Delay in PH diagnosis until after transplant favored early graft loss (p = 0.07). K + L had better kidney graft outcomes than K with death-censored graft survival 95% versus 56% at 3 years (p = 0.011). Among 29 year 2000-09 first transplants (24 K + L), 84% were functioning at 3 years compared to 55% of earlier transplants (p = 0.05). At 6.8 years after transplantation, 46 of 58 patients are living (43 with functioning grafts). Outcomes of transplantation in PH have improved over time, with recent K + L transplantation highly successful. Recurrent oxalosis accounted for a minority of kidney graft losses.

Evidence of true genotype-phenotype correlation in primary hyperoxaluria type 1

A genotype-phenotype correlation in patients with primary hyperoxaluria type 1 and specific AGXT mutations has supposedly been found, at least for sensitivity to medication and long-term outcome. Nevertheless, other determinants, such as environmental factors or modifier genes, must play an essential role in the intra- and interfamilial heterogeneity of this disease. Harambat and co-workers report on this situation, presenting data on a major population of genotyped patients.

Diagnostic examination of the child with urolithiasis or nephrocalcinosis

Urolithiasis and nephrocalcinosis are more frequent in children then currently anticipated, but still remain under- or misdiagnosed in a significant proportion of patients, since symptoms and signs may be subtle or misleading. All children with colicky abdominal pain or macroscopic hematuria should be examined thoroughly for urolithiasis. Also, other, more general, abdominal manifestations can be the first symptoms of renal stones. The patients and their family histories, as well as physical examination, are important initial steps for diagnostic evaluation. Thereafter, diagnostic imaging should be aimed at the location of calculi but also at identification of urinary tract anomalies or acute obstruction due to stone disease. This can often be accomplished by ultrasound examination alone, but sometimes radiological methods such as plain abdominal films or more sensitive non-enhanced computed tomography are necessary. Since metabolic causes are frequent in children, diagnostic evaluation should be meticulous so that metabolic disorders that cause recurrent urolithiasis or even renal failure, such as the primary hyperoxalurias and others, can be ruled out. The stone is not the disease itself; it is only one serious sign! Therefore, thorough and early diagnostic examination is mandatory for every infant and child with the first stone event, or with nephrocalcinosis.

Genotype-phenotype correlation in primary hyperoxaluria type 1: the p.Gly170Arg AGXT mutation is associated with a better outcome

We sought to ascertain the long-term outcome and genotype-phenotype correlations available for primary hyperoxaluria type 1 in a large retrospective cohort study. We examined the clinical history of 155 patients (129 families primarily from Western Europe, North Africa, or the Middle East) as well as the enzymatic or genetic diagnosis. The median age at first symptom was 4 years, and at diagnosis 7.7 years, at which time 43% had reached end-stage renal disease. Presentations included: (1) early nephrocalcinosis and infantile renal failure, (2) recurrent urolithiasis and progressive renal failure diagnosed during childhood, (3) late onset with occasional stone passage diagnosed in adulthood, (4) diagnosis occurring on post-transplantation recurrence, and (5) family screening. The cumulative patient survival was 95, 86, and 74% at ages 10, 30, and 50 years, respectively, with the cumulative renal survival of 81, 59, 41, and 10% at ages 10, 20, 30, and 50 years, respectively; 72 patients had undergone a total of 97 transplantations. Among the 136 patients with DNA analysis, the most common mutation was p.Gly170Arg (allelic frequency 21.5%), with a median age at end-stage renal disease of 47 years for homozygotes, 35 years for heterozygotes, and 21 years for other mutations. Our results underscore the severe prognosis of primary hyperoxaluria type 1 and the necessity for early diagnosis and treatment, as well as confirm a better prognosis of the p.Gly170Arg mutation.

[Biochemical and molecular diagnosis of primary hyperoxaluria type 1: Tunisian study about 15 cases]

BACKGROUND

The primary type 1 hyperoxaluria (HP1) is the most frequent and severe form of the primary hyperoxaluriae. It is related to an enzymatic deficit in alanine glyoxylate aminotransferase (AGT). It is a recessive autosomic disease. Rare in Europe, it is responsible for 13% of the end stage renal failure in the Tunisian child.

AIM

The aim of this work is to evaluate the biological and molecular examinations contributing with the early diagnosis and the follow-up of the HP1 patients and to test their response to pyridoxin.

PATIENTS AND METHODS

A prospective study of 15 children who have oxaluria lower than 500 μmol/l and normal renal function is carried out. The cristalluria study, oxaluria and the glycolate-glycerate urinary ratio were carried out on all the patients. The so-called mutation maghrebean T853 (Ile244 Thr) was detected by direct sequencing of the exon 7 gene AGXT. The response to pyridoxin was tested among 13 patients.

RESULTS

The oxaluria concentration was greater or equal to 1000 μmol/l in nine cases (60%) and ranging between 600 and 1000 μmol/l in the remaining cases. The oxaluria flow was significantly high depending on the age. The glycolaturia was high among eight patients (57%). In 61,5% of the cases, the most frequent crystalline species was whewellite (C1). The "maghrebin" mutation was identified in nine patients at the heterozygous state, showing 25% allelic frequency. The response to pyridoxin was observed in the 13 tested cases.

CONCLUSION

The HP1 is frequent in our country from where the need for an early diagnosis. The use of simple biochemical tools such as the study of the cristalluria, the morphological analysis of stones and the oxaluria allow to direct the diagnosis towards a HP1, confirmed by the glycolaturia determination. The molecular biology is required in the atypical forms.

Indications for combined liver and kidney transplantation in children

A significant number of patients awaiting liver transplantation have associated renal failure and renal dysfunction is associated with increased morbidity and mortality after LT. There has been a recent increase in the number of CLKT in adults. The common indications for CLKT in children are different from those of adults and include metabolic diseases affecting the kidney with or without liver dysfunction and congenital developmental abnormalities affecting both organs. The results are generally encouraging among these groups of patients. Early evaluation and listing of patients before they become severely ill or have major systemic manifestations of their metabolic problem are important.

Primary hyperoxaluria type 1: update and additional mutation analysis of the AGXT gene

Primary hyperoxaluria type 1 (PH1) is an autosomal recessive, inherited disorder of glyoxylate metabolism arising from a deficiency of the alanine:glyoxylate aminotransferase (AGT) enzyme, encoded by the AGXT gene. The disease is manifested by excessive endogenous oxalate production, which leads to impaired renal function and associated morbidity. At least 146 mutations have now been described, 50 of which are newly reported here. The mutations, which occur along the length of the AGXT gene, are predominantly single-nucleotide substitutions (75%), 73 are missense, 19 nonsense, and 18 splice mutations; but 36 major and minor deletions and insertions are also included. There is little association of mutation with ethnicity, the most obvious exception being the p.Ile244Thr mutation, which appears to have North African/Spanish origins. A common, polymorphic variant encoding leucine at codon 11, the so-called minor allele, has significantly lower catalytic activity in vitro, and has a higher frequency in PH1 compared to the rest of the population. This polymorphism influences enzyme targeting in the presence of the most common Gly170Arg mutation and potentiates the effect of several other pathological sequence variants. This review discusses the spectrum of AGXT mutations and polymorphisms, their clinical significance, and their diagnostic relevance.

Effect of conservative treatment on the renal outcome of children with primary hyperoxaluria type 1

Primary hyperoxaluria type 1 results from alanine:glyoxylate aminotransferase deficiency. Due to genotype/phenotype heterogeneity in this autosomal recessive disorder, the renal outcome is difficult to predict in these patients and the long-term impact of conservative management in children is unknown. We report here a multicenter retrospective study on the renal outcome in 27 affected children whose biological diagnosis was based on either decreased enzyme activity or identification of mutations in the patient or his siblings. The median age at first symptoms was 2.4 years while that at initiation of conservative treatment was 4.1 years; 6 children were diagnosed upon family screening. The median follow-up was 8.7 years. At diagnosis, 15 patients had an estimated glomerular filtration rate (eGFR) below 90, and 7 children already had stage 2-3 chronic kidney disease. The median baseline eGFR was 74, which rose to 114 with management in the 22 patients who did not require renal replacement therapy. Overall, 20 patients had a stable eGFR, however, 7 exhibited a decline in eGFR of over 20 during the study period. In a Cox regression model, the only variable significantly associated with deterioration of renal function was therapeutic delay with a relative risk of 1.7 per year. Our study strongly suggests that early and aggressive conservative management may preserve renal function of compliant children with this disorder, thereby avoiding dialysis and postponing transplantation.

The primary hyperoxalurias

The primary hyperoxalurias (PHs) are rare disorders of glyoxylate metabolism in which specific hepatic enzyme deficiencies result in overproduction of oxalate. Due to the resulting severe hyperoxaluria, recurrent urolithiasis or progressive nephrocalcinosis are principal manifestations. End stage renal failure frequently occurs and is followed by systemic oxalate deposition along with its devastating effects. Due to the lack of familiarity with PHs and their heterogeneous clinical expressions, the diagnosis is often delayed until there is advanced disease. In recent years, improvements in medical management have been associated with better patient outcomes. Although there are several therapeutic options that can help prevent early kidney failure, the only curative treatment to date is combined liver-kidney transplantation in patients with type I PH. Promising areas of investigation are being identified. Knowledge of the spectrum of disease expression, early diagnosis, and initiation of treatment before renal failure are essential to realize a benefit for patients.

Etiology of nephrocalcinosis in northern Indian children

This retrospective survey examines the etiology of nephrocalcinosis (NC) in 40 patients (26 boys), over an 8-year period. The median age at onset of symptoms and presentation was 36 months and 72 months, respectively. Clinical features included marked failure to thrive (82.5%), polyuria (60%) and bony deformities (52.5%). The etiology of NC included distal renal tubular acidosis (RTA) in 50% patients and idiopathic hypercalciuria and hyperoxaluria in 7.5% each. Other causes were Bartter syndrome, primary hypomagnesemia with hypercalciuria, severe hypothyroidism and vitamin D excess. No cause for NC was found in 12.5% patients. Specific therapy, where possible, ameliorated the biochemical aberrations, although the extent of NC remained unchanged. At a median (range) follow up of 35 (14-240) months, glomerular filtration rate (GFR) had declined from 82.0 (42-114) ml/min per 1.73 m2 body surface area to 70.8 (21.3-126.5) ml/min per 1.73 m2 body surface area (P = 0.001). Our findings confirm that, even with limited diagnostic facilities, protocol-based evaluation permits determination of the etiology of NC in most patients.

Presentation and role of transplantation in adult patients with type 1 primary hyperoxaluria and the I244T AGXT mutation: Single-center experience

Primary hyperoxaluria type 1 (PH1) is a rare genetic disorder characterized by allelic and clinical heterogeneity. We aim to describe the presentation and full single-center experience of the management of PH1 patients bearing the mutation described in our community (I244T mutation+polymorphism P11L). Since 1983, 12 patients with recurrent renal lithiasis have been diagnosed with PH1 and renal failure in the Canary Islands, Spain. Diagnostic confirmation was based on the presence of oxalosis in undecalcified bone or kidney allograft biopsy, reduced alanine:glyoxylate aminotransferase activity in liver biopsy, and blood DNA analysis. Patients underwent different treatment modalities depending on individual clinical circumstances and therapeutic possibilities at the time of diagnosis: hemodialysis, isolated kidney, simultaneous liver-kidney, or pre-emptive liver transplantation. In all cases, the presentation of advanced renal disease was relatively late (>13 years) and no cases were reported during lactancy or childhood. The eight patients treated with hemodialysis or isolated kidney transplantation showed unfavorable evolution leading to death over a variable period of time. In contrast, the four patients undergoing liver transplantation (three liver+kidney and one pre-emptive liver alone) showed favorable long-term allograft and patient survival (up to 12 years follow-up). In conclusion, in this PH1 population, all bearing the I244T mutation, the development of end-stage renal disease was distinctive during late adolescence or adulthood. Our long-term results support pre-emptive liver transplantation at early stages of renal failure, and kidney-liver transplantation for those with advanced renal disease.

High incidence of hyperoxaluria in generalized peroxisomal disorders

The Zellweger spectrum disorders (ZSDs) are characterized by a generalized loss of peroxisomal functions caused by deficient peroxisomal assembly. Clinical presentation and survival are heterogeneous. Although most peroxisomal enzymes are unstable in the cytosol of peroxisome-deficient cells of ZSD patients, a few enzymes remain stable among which alanine:glyoxylate aminotransferase (AGT). Its deficiency causes primary hyperoxaluria type 1 (PH1, MIM 259900), an inborn error of glyoxylate metabolism characterized by hyperoxaluria, nephrocalcinosis, and renal insufficiency. Despite the normal level of AGT activity in ZSD patients, hyperoxaluria has been reported in several ZSD patients. We observed the unexpected occurrence of renal stones in a cohort of ZSD patients. This led us to perform a study in this cohort to determine the prevalence of hyperoxaluria in ZSDs and to find clinically relevant clues that correlate with the urinary oxalate load. We reviewed medical charts of 31 Dutch ZSD patients with prolonged survival (>1 year). Urinary oxalate excretion was assessed in 23 and glycolate in 22 patients. Hyperoxaluria was present in 19 (83%), and hyperglycolic aciduria in 14 (64%). Pyridoxine treatment in six patients did not reduce the oxalate excretion as in some PH1 patients. Renal involvement with urolithiasis and nephrocalcinosis was present in five of which one developed end-stage renal disease. The presence of hyperoxaluria, potentially leading to severe renal involvement, was statistically significant correlated with the severity of neurological dysfunction. ZSD patients should be screened by urinalysis for hyperoxaluria and renal ultrasound for nephrocalcinosis in order to take timely measures to prevent renal insufficiency.

An overview of the role of genotyping in the diagnosis of the primary hyperoxalurias

The aim of this paper is to give an overview of our current state of knowledge with respect to genotyping for the primary hyperoxalurias and the role of molecular genetics alongside the more traditional biochemical and enzymatic tests for the diagnosis and prognosis of these disorders. The published literature was reviewed to establish the frequency of different mutations and thus the value of testing for a limited number of these mutations in patients with clinical suspicion of primary hyperoxaluria (PH). This approach was compared with whole gene sequencing of the AGXT and GRHPR genes. A limited genetic screen can provide a first line test for PH1 and PH2 in symptomatic patients and can provide a full diagnosis in approximately a third of cases. Molecular genetic analysis is essential for carrier testing and prenatal diagnosis. The value of molecular genetics in prognosis requires a wider evidence base.

Primary hyperoxaluria type 1 in Japan

BACKGROUND/AIMS

Current status of primary hyperoxaluria (PH) has not been surveyed in Japan.

METHODS

Japanese patients with PH were reviewed in the published literature.

RESULTS

Fifty-nine patients were diagnosed as PH from 1962 to 2003. The median ages both at diagnosis and at the onset of initial symptoms were 17 (range: 0.02-63) and 13 (range: 0-58) years, respectively. Twenty-nine (49%) patients were older than 20 years at diagnosis, among whom 26 (90%) already presented end-stage renal failure (ESRF) or soon evolved into ESRF. Among 30 (51%) diagnosed as PH under 20 years old, only 13 (43%) were already in a terminal stage of renal insufficiency. Ten patients were diagnosed as PH1 by liver biopsy. We identified two types of enzymatic phenotypes in 3 of those patients examined. In 1 case, immunoreactive SPT/AGT protein level was very low due to accelerated proteolysis, while in other 2 cases, the immunoreactivity was detected on mitochondria due to mistargeting. Of 9 cases having been subjected to kidney transplantation at a median age of 20 years (range 7.3-40.0), it was only 2 cases that were reported to be successful, while the median survival time of the kidney grafts being 1.4 years (range 0-7). Of 4 patients having undergone combined liver/kidney transplantations (at the ages of 1.3, 1.4, 9 and 41 years, respectively), the surgery was successful in 3 cases; in the remaining one case, however, rejection required removal of the transplanted kidney was observed. The overall survival ratio of all the 59 PH cases accounted for 77, 71 and 55% at 5, 10 and 20 years, respectively.

CONCLUSION

Assuming that the majority of the 59 patients with PH reported was classified as PH1, it is postulated that morbidity of violent infantile PH1 in Japan might be less than those in the USA and Europe, and symptoms of elderly Japanese PH1 patients seem to be milder than those of Western patients. Establishment of an early detection system of PH1 and more popular application of combined liver/kidney transplantation deserve further study.

A 20-year experience of combined liver/kidney transplantation for primary hyperoxaluria (PH1): the European PH1 transplant registry experience 1984-2004

Primary hyperoxaluria (PH1) is a condition caused by a hepatic-based enzyme defect which can lead to renal failure due to oxalate stone disease, obstructive uropathy and nephrocalcinosis. It has been shown that the underlying metabolic defect can be corrected by liver transplantation and in most cases (renal failure having already occurred) is accompanied by a kidney graft. This paper describes the current results of 127 liver transplants performed in 117 patients over a 20-year period from 1984 to 2004 in 35 European centres. The mean age at onset of symptoms was 5.6 +/- 7.8 years and the mean age at which a diagnosis was made was 8.8 +/- 9.5 years. The diagnosis was confirmed by liver biopsy proven decreased AGT activity in 68% of cases, hyperoxaluria in 74%, hyperglycolicaciduria in 37% and hyperoxalaemia in 50%. Patients were transplanted at a mean age of 16.5 +/- 11.4 years following a period of dialysis of 3.2 +/- 3.2 years (range 0-14.4 years). 1-, 5- and 10-year patient survival values were 86, 80 and 69%, respectively, and liver graft survival rates of 80, 72 and 60% at the same time intervals. There have been 27 deaths and 10 liver retransplants have been carried out. Patient outcomes are improved when prolonged periods on dialysis and the complications of systemic oxalosis have not occurred.

Primary hyperoxaluria--the German experience

BACKGROUND

Primary hyperoxaluria (PH) is a heterogeneous disease with variable age of onset and inconsistent progression into renal failure (ESRF).

AIMS

In 1994 we initiated a survey within our Pediatric Nephrology working group to ascertain epidemiologic data and current practices. Updates were performed in 2000 and 2004.

RESULTS

Diagnosis of PH was made in 65 patients (42 with PH type I, 3 with PH type II, 12 unclassified and 8 reported dead), which suggests a minimum prevalence of 0.7 per 1 million of the population. First symptoms were urolithiasis, nephrocalcinosis, urinary tract infection or hematuria. Diagnosis was often delayed and was made only in ESRF in 11% of patients. Measurement of urine metabolites or plasma oxalate in ESRF was performed in 76 and 57%, respectively. Determination of enzyme activity in liver biopsy (55% overall) and mutation analysis have increasingly been performed since 2000 (84.2 and 51%). Treatment included high fluid intake, pyridoxine, citrate and magnesium preparations. Pyridoxine response was reported in 21% of patients. No genotype/phenotype correlation was seen. Most patients (39) do not require renal replacement therapy, 5 patients receive chronic hemodialysis. Preemptive liver (n = 5) and combined liver-kidney transplantation (n = 9) were the preferred transplantation procedures.

CONCLUSION

Despite increasing knowledge and awareness, diagnosis of PH is still too often delayed and diagnosis only made in ESRF. Most German patients, however, do currently not require renal replacement therapy. Genotype/phenotype correlations were not found. Combined liver kidney transplantation is the preferred procedure, but has its specific risks. Additional treatment options are clearly needed.

The primary hyperoxalurias: an algorithm for diagnosis

BACKGROUND/AIMS

The primary hyperoxalurias (PHs) are inborn errors of metabolism resulting in increased urinary excretion of oxalate. Nephrolithiasis, nephrocalcinosis, and renal failure result. Renal failure can occur as early as infancy or as late as the sixth decade of life, and if not addressed promptly, results in severe morbidity and mortality related to systemic oxalate deposition (oxalosis). Clinicians are likely to encounter few PH patients during a practicing lifetime. Definitive diagnosis requires special studies performed in only a small number of laboratories worldwide. Accordingly, delays in diagnosis are common.

METHODS

An evidence-based guideline for diagnosis was developed.

RESULTS

Patients with stones or nephrocalcinosis in childhood, recurrent calcium oxalate stones in adulthood, or renal insufficiency associated with stones or nephrocalcinosis should be evaluated for PH. A systematic approach to measurement of urine oxalate, glycolate and glycerate, and plasma oxalate is provided. Age-related variation in urine oxalate requires attention to normal ranges. Molecular analysis for mutations of the AGXT gene (PH, type I) or GRHPR gene (PH, type II) is definitive in some patients, while liver enzyme analysis is required for confirmation of the diagnosis in the remainder.

CONCLUSION

An evidence-based algorithm will facilitate recognition and diagnosis of patients with the PHs, permitting earlier treatment.

Clinical implications of mutation analysis in primary hyperoxaluria type 1

BACKGROUND

Primary hyperoxaluria type 1 (PH1) is an inborn error of glyoxylate metabolism with an extensive clinical and genetic heterogeneity. Although over 50 disease-causing mutations have been identified, the relationship between genotype and clinical outcome remains unclear. The aim of this study was to determine this association in order to find clues for improvement of patient care.

METHODS

AGXT mutation analysis and assessment of biochemical characteristics and clinical outcome were performed on patients from a Dutch PH1 cohort.

RESULTS

Thirty-three of a cohort of 57 PH1 patients, identified in The Netherlands over a period of 30 years, were analyzed. Ten different mutations were found. The most common mutations were the Gly170Arg, Phe152Ile, and the 33insC mutations, with an allele frequency of 43%, 19%, and 15%, respectively. Homozygous Gly170Arg and Phe152Ile mutations were associated with pyridoxine responsiveness and a preserved renal function over time when treatment was timely initiated. All patients homozygous for the 33insC mutation had end-stage renal disease (ESRD) before the first year of age. In two unrelated patients, a new Val336Asp mutation was found coupled with the Gly170Arg mutation on the minor allele. We also found 3 patients homozygous for a novel Gly82Arg mutation with adverse outcome in 2 of them.

CONCLUSION

Early detection of Gly170Arg and Phe152Ile mutations in PH1 has important clinical implications because of their association with pyridoxine responsiveness and clinical outcome. The association of a homozygous 33insC mutation with severe infantile ESRD, resulting in early deaths in 2 out of 3 cases, warrants a choice for prenatal diagnostics in affected families.

Genetic heterogeneity in primary hyperoxaluria type 1: impact on diagnosis

Primary hyperoxaluria type 1 (PH1) is an autosomal recessive disease characterized by progressive kidney failure due to renal deposition of calcium oxalate. The disease is caused by a deficiency of alanine:glyoxylate aminotransferase (AGT) which catalyzes the conversion of glyoxylate to glycine. When AGT is absent, glyoxylate is converted to oxalate which forms insoluble calcium salts that accumulate in the kidney and other organs. In the most common phenotype there is a unique phenomenon wherein AGT is mis-targeted to the mitochondria instead of the peroxisomes. The diagnosis of PH1 is complicated by heterogeneity of clinical presentation, course of the disease, biochemical markers, AGT enzymatic activity and genotype. More than 50 mutations and polymorphisms have been reported in the AGT gene; three common mutations accounting for almost 50% of PH1 alleles. The mutations are of all types, with missense making up the largest fraction. There are some mutations with apparent ethnic associations and at least one that appears to be pan-ethnic. Although correlations can in some cases be made between biochemical phenotype and genotype, correlation with clinical phenotype is complicated by the involvement of other genetic and non-genetic factors that affect disease severity. A number of polymorphisms have been described in the AGT gene some of which cause missense changes and, in some cases, alter enzyme activity. As DNA testing becomes more commonly used for diagnosis it is important to correlate observed sequence changes with previously documented changes as an aid to assessing their potential significance.