We report a classic cystic fibrosis (CF) boy with a large deletion of exons 4–11 in the cystic fibrosis transmembrane conductance regulator (CFTR) gene on one allele and p.Phe508del in exon 10 on the second allele. Both parents of Georgian and Ukrainian background had no personal or family history of the disease. The initial molecular diagnostic investigation identified the patient as homozygous for the p.Phe508del and not compatible with his parent’s genetic status. The possibility of nonpaternity or uniparental disomy (UPD7) was investigated and excluded using microsatellite analysis of highly polymorphic markers on chromosome 7. Array-CGH was also performed on the patient and revealed a male profile with a subtle deletion within the CFTR gene on the long arm (q-arm) of chromosome 7 (7q31.2). The deletion was confirmed by MLPA extending from probe L02380 to probe L14978 (28.7？kb) and that was inherited from his father, while p.PheF508del was inherited from his mother. These data highlight the need for additional testing for large deletions in patients with apparent homozygosity for a mutated CFTR allele that do not match the carrier status of the parents. Not testing can lead to misdiagnosis and misinterpretation of mutation carrier status and the expected penetrance of the disorder. 1. Introduction Cystic fibrosis (CF) is an autosomal recessive disorder caused by mutations in the CF conductance transmembrane regulator (CFTR) gene [1, 2]. The CFTR gene spans an approximately 240？kb region on chromosome 7q31.3 and codes for 1480 amino acid protein that functions as a cAMP chloride channel in exocrine epithelia [3]. This channel regulates water and ion transport across membranes and is found in the epithelium of secretory epithelial cells in the lungs, liver, pancreas, intestine, reproductive tracts, and sweat glands. Mutations in the CFTR gene are responsible for both the classical and atypical presentations of the disease, including pulmonary disease, pancreatic insufficiency, malabsorption, meconium ileus, failure to thrive, infertility, and elevated concentrations of chloride in sweat [4, 5]. Currently, 1964 CFTR mutations have been listed in the CF database (http://www.genet.sickkids.on.ca/cftr/, accessed 3 February, 2014), 39 of which constitute 90% of mutations found in the Caucasian populations. In patients with CF, the differentiation between true and apparent homozygosity for CFTR mutations is critical for correct prenatal diagnosis of CF, as well as for genetic counseling of the CF patient and his/her family members [6, 7]. Therefore, when
References
[1]
J. M. Rommens, M. C. Iannuzzi, B.-S. Kerem et al., “Identification of the cystic fibrosis gene: chromosome walking and jumping,” Science, vol. 245, no. 4922, pp. 1059–1065, 1989.
[2]
F. S. Collins, “Cystic fibrosis: molecular biology and therapeutic implications,” Science, vol. 256, no. 5058, pp. 774–779, 1992.
[3]
C. E. Bear, C. Li, N. Kartner et al., “Purification and functional reconstitution of the cystic fibrosis transmembrane conductance regulator (CFTR),” Cell, vol. 68, no. 4, pp. 809–818, 1992.
[4]
M. J. Welsh, “Gene transfer for cystic fibrosis,” Journal of Clinical Investigation, vol. 104, no. 9, pp. 1165–1166, 1999.
[5]
T. S. Cohen and A. Prince, “Cystic fibrosis: a mucosal immunodeficiency syndrome,” Nature Medicine, vol. 18, no. 4, pp. 509–519, 2012.
[6]
F. M. Hantash, A. Rebuyon, M. Peng, J. B. Redman, W. Sun, and C. M. Strom, “Apparent homozygosity of a novel frame shift mutation in the CFTR gene because of a large deletion,” Journal of Molecular Diagnostics, vol. 11, no. 3, pp. 253–256, 2009.
[7]
A. Diana, R. Tesse, A. M. Polizzi et al., “A large deletion causes apparent homozygosity for the D1152H mutation in the cystic fibrosis transmembrane regulator (CFTR) gene,” Gene, vol. 497, no. 1, pp. 90–92, 2012.
[8]
F. Chevalier-Porst, A.-M. Bonardot, J.-P. Chazalette, M. Mathieu, and D. Bozon, “40 kilobase deletion (CF 40 kb del 4-10) removes exons 4 to 10 of the cystic fibrosis transmembrane conductance regulator gene,” Human Mutation, vol. 10, supplement 1, pp. S291–S294, 1998.
[9]
B. E. Carlyle, D. S. Borowitz, and P. L. Glick, “A review of pathophysiology and management of fetuses and neonates with meconium ileus for the pediatric surgeon,” Journal of Pediatric Surgery, vol. 47, no. 4, pp. 772–781, 2012.
[10]
G. Casaccia, A. Trucchi, A. Nahom et al., “The impact of cystic fibrosis on neonatal intestinal obstruction: the need for prenatal/neonatal screening,” Pediatric Surgery International, vol. 19, no. 1-2, pp. 75–78, 2003.
[11]
P. K. Yiallouros, V. Neocleous, M. Zeniou et al., “Cystic fibrosis mutational spectrum and genotypic/phenotypic features in Greek-Cypriots, with emphasis on dehydration as presenting symptom,” Clinical Genetics, vol. 71, no. 3, pp. 290–292, 2007.
[12]
M. Schneider, F. Joncourt, J. Sanz, T. Von K？nel, and S. Gallati, “Detection of exon deletions within an entire gene (CFTR) by relative quantification on the LightCycler,” Clinical Chemistry, vol. 52, no. 11, pp. 2005–2012, 2006.
[13]
R. Tomaiuolo, F. Sangiuolo, C. Bombieri et al., “Epidemiology and a novel procedure for large scale analysis of CFTR rearrangements in classic and atypical CF patients: a multicentric Italian study,” Journal of Cystic Fibrosis, vol. 7, no. 5, pp. 347–351, 2008.
[14]
F. M. Hantash, A. Milunsky, Z. Wang et al., “A large deletion in the CFTR gene in CBAVD,” Genetics in Medicine, vol. 8, no. 2, pp. 93–95, 2006.
[15]
F. M. Hantash, J. B. Redman, K. Starn et al., “Novel and recurrent rearrangements in the CFTR gene: clinical and laboratory implications for cystic fibrosis screening,” Human Genetics, vol. 119, no. 1-2, pp. 126–136, 2006.
[16]
M. Taulan, V. Viart, C. Theze et al., “Identification of a novel duplication CFTRdup2 and functional impact of large rearrangements identified in the CFTR gene,” Gene, vol. 500, no. 2, pp. 194–198, 2012.
[17]
F. Niel, J. Martin, F. Dastot-Le Moal et al., “Rapid detection of CFTR gene rearrangements impacts on genetic counselling in cystic fibrosis,” Journal of medical genetics, vol. 41, no. 11, p. e118, 2004.
[18]
V. Paracchini, M. Seia, D. Coviello et al., “Molecular and clinical features associated with CFTR gene rearrangements in Italian population: identification of a new duplication and recurrent deletions,” Clinical Genetics, vol. 73, no. 4, pp. 346–352, 2008.
