Primary Hyperoxaluria Type 1: Update and Additional Mutation Analysis of the AGXT Gene

Clinical Biochemistry, University College London (UCL) Hospitals National Health Service (NHS) Trust, London, UK.
Human Mutation (Impact Factor: 5.14). 06/2009; 30(6):910-7. DOI: 10.1002/humu.21021
Source: PubMed


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.

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    • "This is particularly relevant for those with PH1 since several mutations, most notably c.508G>A, have increased pathogenicity when associated with the minor allele (see Williams et al. 2009 for review). Although it was originally reported that the c.32C>T, c.264C>T, and c.1020A>G variants are in complete linkage disequilibrium , it has since been established that the linkage breaks down in some cases, as reviewed in Williams et al. 2009. "
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    ABSTRACT: Definitive diagnosis of primary hyperoxaluria (PH) currently utilizes sequential Sanger sequencing of the AGXT, GRPHR, and HOGA1 genes but efficacy is unproven. This analysis is time-consuming, relatively expensive, and delays in diagnosis and inappropriate treatment can occur if not pursued early in the diagnostic work-up. We reviewed testing outcomes of Sanger sequencing in 200 consecutive patient samples referred for analysis. In addition, the Illumina Truseq custom amplicon system was evaluated for paralleled next-generation sequencing (NGS) of AGXT, GRHPR, and HOGA1 in 90 known PH patients. AGXT sequencing was requested in all patients, permitting a diagnosis of PH1 in 50%. All remaining patients underwent targeted exon sequencing of GRHPR and HOGA1 with 8% diagnosed with PH2 and 8% with PH3. Complete sequencing of both GRHPR and HOGA1 was not requested in 25% of patients referred leaving their diagnosis in doubt. NGS analysis showed 98% agreement with Sanger sequencing and both approaches had 100% diagnostic specificity. Diagnostic sensitivity of Sanger sequencing was 98% and for NGS it was 97%. NGS has comparable diagnostic performance to Sanger sequencing for the diagnosis of PH and, if implemented, would screen for all forms of PH simultaneously ensuring prompt diagnosis at decreased cost.
    Full-text · Article · Nov 2014
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    • "More than 150 different pathogenic mutations, including nonsense, frameshift, and missense mutations, in the AGXT gene that cause PH1 have been identified to date ( While nonsense and frameshifts are null mutations that lead to the complete loss of the gene product, the most common type of AGXT mutations are single amino-acid substitutions that lead to the synthesis of an aberrant gene product [6]. These mutations are found throughout the entire gene and cause a wide spectrum of clinical severity. "
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    ABSTRACT: Background Primary hyperoxaluria type 1 is a rare autosomal recessive disease of glyoxylate metabolism caused by a defect in the liver-specific peroxisomal enzyme alanine:glyoxylate aminotransferase (AGT) that leads to hyperoxaluria, recurrent urolithiasis, and nephrocalcinosis. Methods Two unrelated patients with recurrent urolithiasis, along with members of their families, exhibited mutations in the AGXT gene by PCR direct sequencing. Results Two heterozygous mutations that predict truncated proteins, p.S81X and p.S275delinsRAfs, were identified in one patient. The p.S81X mutation is novel. Two heterozygous missense mutations, p.M1T and p.I202N, were detected in another patient but were not identified in her sibling. These four mutations were confirmed to be of paternal and maternal origin. Conclusions These are the first cases of primary hyperoxaluria type 1 to be diagnosed by clinical manifestations and AGXT gene mutations in mainland China. The novel p.S81X and p.I202N mutations detected in our study extend the spectrum of known AGXT gene mutations.
    Full-text · Article · Jun 2014 · BMC Nephrology
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    • "In some cases, the addition of a second mutation appears to have primarily a destabilizing role, acting together with Leu11 to generate a severely destabilized and thus non-functional enzyme. In other cases, the mutations have more complex effects on protein trafficking [6], [11]. For example, a G170R mutation found on the minor allele is observed in ∼30% of PH1 patients [2]. "
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    ABSTRACT: Primary Hyperoxaluria Type 1 (PH1) is a rare autosomal recessive kidney stone disease caused by deficiency of the peroxisomal enzyme alanine: glyoxylate aminotransferase (AGT), which is involved in glyoxylate detoxification. Over 75 different missense mutations in AGT have been found associated with PH1. While some of the mutations have been found to affect enzyme activity, stability, and/or localization, approximately half of these mutations are completely uncharacterized. In this study, we sought to systematically characterize AGT missense mutations associated with PH1. To facilitate analysis, we used two high-throughput yeast-based assays: one that assesses AGT specific activity, and one that assesses protein stability. Approximately 30% of PH1-associated missense mutations are found in conjunction with a minor allele polymorphic variant, which can interact to elicit complex effects on protein stability and trafficking. To better understand this allele interaction, we functionally characterized each of 34 mutants on both the major (wild-type) and minor allele backgrounds, identifying mutations that synergize with the minor allele. We classify these mutants into four distinct categories depending on activity/stability results in the different alleles. Twelve mutants were found to display reduced activity in combination with the minor allele, compared with the major allele background. When mapped on the AGT dimer structure, these mutants reveal localized regions of the protein that appear particularly sensitive to interactions with the minor allele variant. While the majority of the deleterious effects on activity in the minor allele can be attributed to synergistic interaction affecting protein stability, we identify one mutation, E274D, that appears to specifically affect activity when in combination with the minor allele.
    Full-text · Article · Apr 2014 · PLoS ONE
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