title: Selected exonic sequencing of the AGXT gene provides a genetic diagnosis in 50% of patients with primary hyperoxaluria type 1.
abstract: BACKGROUND
  Definitive diagnosis of primary hyperoxaluria type 1 (PH1) requires analysis of alanine:glyoxylate aminotransferase (AGT) activity in the liver. We have previously shown that targeted screening for the 3 most common mutations in the AGXT gene (c.33_34insC, c.508G>A, and c.731T>C) can provide a molecular diagnosis in 34.5% of PH1 patients, eliminating the need for a liver biopsy. Having reviewed the distribution of all AGXT mutations, we have evaluated a diagnostic strategy that uses selected exon sequencing for the molecular diagnosis of PH1.
  
  
  METHODS
  We sequenced exons 1, 4, and 7 for 300 biopsy-confirmed PH1 patients and expressed the identified missense mutations in vitro.
  
  
  RESULTS
  Our identification of at least 1 mutation in 224 patients (75%) and 2 mutations in 149 patients increased the diagnostic sensitivity to 50%. We detected 29 kinds of sequence changes, 15 of which were novel. Four of these mutations were in exon 1 (c.2_3delinsAT, c.30_32delCC, c.122G>A, c.126delG), 7 were in exon 4 (c.447_454delGCTGCTGT, c.449T>C, c.473C>T, c.481G>A, c.481G>T, c.497T>C, c.424-2A>G), and 4 were in exon 7 (c.725insT, c.737G>A, c.757T>C, c.776 + 1G>A). The missense changes were associated with severely decreased AGT catalytic activity and negative immunoreactivity when expressed in vitro. Missense mutation c.26C>A, previously described as a pathological mutation, had activity similar to that of the wild-type enzyme.
  
  
  CONCLUSIONS
  Selective exon sequencing can allow a definitive diagnosis in 50% of PH1 patients. The test offers a rapid turnaround time (15 days) with minimal risk to the patient. Demonstration of the expression of missense changes is essential to demonstrate pathogenicity.
authors.affiliation: Clinical Biochemistry, University College London Hospitals, London, United Kingdom.
authors.forename: Emma
authors.initials: E
authors.lastname: Williams
authors.forename: Gill
authors.initials: G
authors.lastname: Rumsby
mesh_terms: D005091:Exons; D006801:Humans; D006960:Hyperoxaluria, Primary / Q000175:diagnosis* / Q000235:genetics; D025202:Molecular Diagnostic Techniques; D020125:Mutation, Missense; D022821:RNA Splice Sites; D012680:Sensitivity and Specificity; D017422:Sequence Analysis, DNA; D000637:Transaminases / Q000235:genetics*
chemical_list: D022821:RNA Splice Sites; D000637:Transaminases; C019635:Alanine-glyoxylate transaminase