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Dalia Consuelo Guadarrama Vallejo, Juan C Zenteno, Arturo Flores Cuevas; Identification of RB1 gene germline mutations in Mexican patients with sporadic unilateral retinoblastoma. Invest. Ophthalmol. Vis. Sci. 2015;56(7 ):81.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: to determinate the percentage of cases with sporadic unilateral retinoblastoma carrying RB1 gene germline mutations in a sample of Mexican patients.
Methods: an observational, cross-sectional and descriptive study was performed; patients with sporadic (non-familial) unilateral retinoblastoma evaluated between March 2005 and December 2011 in a reference center in Mexico City were selected. Inclusion criteria were both genders, older than 12 months, and unilateral tumor. Patients with a family history of fibrosarcoma, lymphoma, leukemia, or melanoma were excluded. Patients developing contralateral retinoblastoma during the study were eliminated.<br /> Genomic DNA was obtained from peripheral blood leukocytes in each patient; PCR amplification and direct nucleotide sequencing of the 27 exons and exon/intron junctions of the RB1 gene was performed. Possible gross gene deletions or duplications were investigated by means of MLPA (Multiplex Ligation-Dependent Probe Analysis). In addition, promoter sequencing and DNA methylation analyses were performed. Potential pathogenicity of novel mutations was analyzed with PolyPhen software.
Results: Twenty (9 female and 11 male) Mexican patients with sporadic unilateral retinoblastoma were included; average age at diagnosis was 26.3 months. Germline mutations were identified in two patients (10%): a mutation in exon 17 predicting a nonsense mutation at residue 533 and a mutation in exon 20 predicting a p.R661W missense mutation. Parental DNA’s of these two cases were negative for the mutations, indicating de novo origin. No mutations in exonic or promoter regions or methylation of the RB1 promoter were demonstrated in the remaining 18 patients.
Conclusion: This is the first study in Mexican population using a number of molecular diagnostic tests to identify RB1 germline defects in unilateral retinoblastoma. Our results contrast with figures from other populations showing up to 20% of RB1 mutations in sporadic unilateral retinoblastoma. Our results are of extreme importance for genetic counselling in this group of retinoblastoma patients and their families.
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