Following amplification, PCR products were digested using 10 U of restriction enzyme Msp I (New England BioLabs, Beverly, MA, USA) for 16 h at 37°C, and electrophoresed on a 3% agarose gel. The wild type Arg allele for codon 194 is determined by the presence of a band at 292 bp, while the mutant Trp allele is determined by the presence of a band at 313 bp (indicative of the absence

of the Msp I cutting site). In addition to these bands, a 174 bp band, resulting from an additional invariant cutting site for Msp I in the 491 bp amplified fragment (codon 194) is always present and serves as internal control for complete Msp I digestion. The wild type Arg allele for codon 399 is determined by the presence SIS 3 of two bands at 374 and 221 bp, while the mutant Gln allele is determined by MG-132 the presence of the uncut 615 bp band (indicative of the absence of the Msp I cutting site). Data analysis The CBL-0137 cost allelic frequencies were estimated by gene counting and genotypes were scored.

The χ2 test was used to compare the observed numbers of genotypes with those expected for a population in the Hardy-Weinberg equilibrium and to test the significance of the differences of observed alleles and genotypes between groups. The odds ratios (ORs) and 95% confidence intervals (CIs) were calculated by using a logistic regression model. The t-test (for normal distribution) or Manne-Whitney test (for non-normal distribution) was used to compare each parameter between two groups

(i.e. sex and age). An analysis of variance test was used to identify parameters that would make significant differences Pyruvate dehydrogenase lipoamide kinase isozyme 1 between more than two groups; Scheffe’s test was then used to assess the significance of difference in each identified parameter between any two groups. STATISTICA 6.0 software (Statsoft, Tulsa, OK, USA) was used to perform analyses. Results and discussion In this work we investigated two common single nucleotide polymorphisms of XRCC1 gene Arg194Trp and Arg399Gln and their association with human head and neck squamous cell carcinoma. The genotype analysis of these two SNPs of XRCC1 gene, for 92 HNSCC patients and 124 controls of cancer free subjects, in Polish population were performed using PCR-RFLP method. The polymorphisms chosen for this study have been shown to have functional significance and may be responsible for a low DNA repair capacity phenotype characteristic of cancer patients including head and neck squamous carcinomas [29–32]. The characteristic of HNSCC patens group according to age, sex, tumor stage and smoking status data was displayed in table 1. Table 1 The characteristic of patients group with squamous cell carcinoma of the head and neck (HNSCC). Patients Sex Tumor stage (TNM) Smoking status (cigarettes per day) No.