Short Communication A double mutation in AGXT gene in families with primary hyperoxaluria type 1 Houda Kanoun a, ⁎, Faiçal Jarraya b , Ikhlass Hadj Salem a , Hichem Mahfoudh b , Yosr Chaabouni b , Fatma Makni c , Jamil Hachicha b , Faiza Fakhfakh a a Laboratoire de Génétique Moléculaire Humaine, Faculté de Médecine de Sfax, Université de Sfax, Tunisia b Unité de Recherche UR12ES14 et Service de Néphrologie, Hôpital Hédi Chaker, Sfax, Tunisia c Laboratoire de Biochimie, Hôpital Habib Bourguiba, Sfax, Tunisia abstract article info Article history: Accepted 26 August 2013 Available online 5 September 2013 Keywords: Primary hyperoxaluria type 1 AGT AGXT gene mutation Intrafamilial heterogeneity Primary hyperoxaluria type 1 (PH1) is a severe autosomal recessive inherited disorder of glyoxylate metabolism caused by mutations in the AGXT gene on chromosome 2q37.3 that encodes the hepatic peroxisomal enzyme alanine:glyoxylate aminotransferase. These mutations are found throughout the entire gene and cause a wide spectrum of clinical severity. Rare in Europe, PH1 is responsible for 13% of the end stage renal failure in the Tunisian child. In the present work, we identified the double mutation c.32CNT (Pro11Leu) and c.731TNC (p.Ile244Thr) in AGXT gene in five unrelated Tunisian families with PH1 disease. Our results provide evidence regarding the potential involvement of c.32CNT, originally described as common polymorphism, on the resulting phenotype. We also reported an extreme intrafamilial heterogeneity in clinical presentation of PH1. Despite the same genetic background, the outcome of the affected members differs widely. The significant phenotypic heterogeneity observed within a same family, with a same genotype, suggests the existence of relevant modifier factors. © 2013 Elsevier B.V. All rights reserved. 1. Introduction Primary hyperoxaluria type 1 (PH1; OMIM # 259900) is an autoso- mal recessive inherited disorder caused by deficiency of the liver perox- isomal enzyme alanine:glyoxylate aminotransferase (AGT; EC 2.6.1.44), which is important in the detoxification of glyoxylate (Danpure, 2001; Harambat et al., 2011). The AGT deficiency in PH1 is responsible for an increased endogenous production and urinary excretion of oxalate that lead to hyperoxaluria. The excess of oxalate is combined with calci- um to form insoluble calcium oxalate (CaOx) crystals that accumulate in the kidneys and urinary tract. Recurrent urolithiasis and progressive nephrocalcinosis, therefore, represent the principal manifestations of PH1 that lead, subsequently, to end-stage renal disease (ESRD) and sys- temic oxalosis in the absence of appropriate conservative treatment (Hoppe et al., 2009). PH1 represents the most common and severe type of primary hyperoxalurias. In Tunisia, a country with a high rate of consanguinity, this disease is responsible for 13% of ESRD in children compared to 0.3% in Europe and 0.7% in North America (Kamoun and Lakhoua, 1996). AGT catalytic activity measurement is essential for definitive diagnosis of PH1. In the absence of this biopsy and as an alternative approach, DNA analysis allows a non invasive method to establish the PH1's diagnosis in most of suspected patients. The AGXT gene, which encodes the 392 amino acid protein AGT, has been mapped to chromosome 2q37.3. It consists of 11 exons spanning approximately 10 kb. Currently, all over the world, over 160 distinct mutations have so far been reported throughout the 11 exons of the AGXT gene as the cause of a wide spectrum of clinical severity (http:// www.hgvs.org/rec.html)(Williams et al., 2009). Approximately 75% of mutant alleles are of single nucleotide substitution type, particularly missense mutations. The remainders are null mutations (deletion/ insertion, nonsense and splice site mutations). For the majority of vari- ants, the consequences on their pathogenicity have been established. These changes affect the AGT activity by the involvement of more than one mechanism. The functional deficiency of AGT in PH1 resulted in its conformational defect or in its mistargeting to the mitochondria instead of the hepatic peroxisomes (Purdue et al., 1991). Actually, for some AGXT variants, experimental demonstration of their pathogenicity cannot be assumed. They need be in association with other changes to have relevance. This is the notion of ‘double mutation’ observed also in other diseases (Savoy et al., 1995). In this study, we performed a molecular genetic analysis of the AGXT gene in 13 Tunisian patients from five unrelated consanguineous families with PH1 syndrome. We identified a double mutation c.32CNT and c.731TNC in AGXT gene in all patients. Gene 531 (2013) 451–456 Abbreviations: PH1, primary hyperoxaluria type 1; AGT, alanine:glyoxylate amino- transferase; CaOx, calcium oxalate; ESRD, end-stage renal disease; PCR, polymerase chain reaction; rmsd, root mean square deviation. ⁎ Corresponding author at: Laboratoire de Génétique Moléculaire Humaine, Faculté de Médecine de Sfax, Avenue Magida Boulila, 3029 Sfax, Tunisia. Tel.: +216 74 24 18 88; fax: +216 74 46 14 03. E-mail address: houda.kanoun@gmail.com (H. Kanoun). 0378-1119/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.gene.2013.08.083 Contents lists available at ScienceDirect Gene journal homepage: www.elsevier.com/locate/gene