['Environmental and genetic factors may modify or contribute to the phenotypic differences observed in multigenic and monogenic diseases, such as cystic fibrosis (CF). An analysis of modifier genes can be helpful for estimating patient prognosis and directing preventive care. The aim of this study is to determine the association between seven genetic variants of four modifier genes and CF by comparing their corresponding allelic and genotypic frequencies in CF patients (n\u200a=\u200a81) and control subjects (n\u200a=\u200a104). Genetic variants of MBL2 exon 1 (A, B, C and D), the IL-8 promoter (-251 A/T), the TNFα promoter (TNF1/TNF2), and SERPINA1 (PI*Z and PI*S) were tested in CF patients and control subjects from northeastern Mexico by PCR-RFLP.', 'The TNF2 allele (P\u200a=\u200a0.012, OR 3.43, 95% CI 1.25-9.38) was significantly associated with CF under the dominant and additive models but was not associated with CF under the recessive model. This association remained statistically significant after adjusting for multiple tests using the Bonferroni correction (P\u200a=\u200a0.0482). The other tested variants and genotypes did not show any association with the disease.'] Is the tumor necrosis factor α ( -308 A/G ) polymorphism associated with cystic fibrosis in Mexican patients?