Association between rs61764370, rs9266, and rs140080026 polymorphisms of the KRAS gene and breast cancer risk in a Mexican population

OBJECTIVE

Polymorphisms of the KRAS gene have been shown to be associated with cancer. However, their association with breast cancer (BC) has been inconsistent. The purpose of this study was to determine the frequency with which the rs61764370, rs9266, and rs140080026 polymorphisms of the KRAS gene are associated with BC in patients of the Mexican population.

PATIENTS AND METHODS

The rs61764370 A>C or T>G and rs140080026 A>G polymorphisms were determined by Polymerase Chain Reaction (PCR), and the rs9266 A>G polymorphism was determined by DNA sequencing of healthy Mexican subjects and BC patients.

RESULTS

We observed that 78% of BC patients are overweight and/or obese, 57% have metastatic lymph nodes, 64% have luminal A/B cancer subtypes, and 61% have stage III-IV cancer. The rs61764370 polymorphism was associated with BC susceptibility when the BC patients and the control group were compared for the AC genotype (p = 0.020), AC vs. AA genotypes (heterozygous model: p = 0.016), AC/CC genotype (dominant model: p = 0.002), and the C allele (p = 0.007). The AC/CC genotype (p = 0.018; rs61764370) and AG/GG genotype (p = 0.005; rs9266) were associated with age in BC patients ≥50 years old. The AC/CC (rs61764370) and AG/GG (rs9266) genotypes were classified by molecular subtype, TNM stage, miscarriage, lymph node metastasis, ductal type, and Ki-67. These classifications were also associated with BC patients, indicating that these factors may significantly contribute to BC risk. The AAA (OR 0.65, 95% CI 0.43-0.98, p = 0.039) and CAA (OR 3.25, 95% CI 1.13-9.36, p = 0.021) haplotypes were also associated with BC susceptibility. In addition, 94 polymorphisms were identified on the 3'UTR of the KRAS gene GRCh 38/hg3 (25,209,490-25,209,122) in BC (n = 112) and control (n = 113) samples. However, 92 of these polymorphisms have only expressed the major allele (wild-type allele).

CONCLUSIONS

The rs61764370 polymorphism in the KRAS gene was associated with BC susceptibility in the Mexican population. The dominant model of the rs61764370 and rs9266 polymorphisms (classified by molecular subtype, miscarriage, TNM stage, lymph node metastasis, and Ki-67) could significantly contribute to BC risk in patients ≥50 years. The CAA haplotype could significantly contribute to BC risk in the Mexican population analyzed.

Three novel HBB mutations, c.-140C>G (-90 C>G), c.237_256delGGACAACCTCAAGGGCACCT (FS Cd 78/85 -20 bp), and c.315+2T>G (IVS2:2 T>G). Update of the mutational spectrum of β-Thalassemia in Mexican mestizo patients

INTRODUCTION

Beta-thalassemia (β-thal) is frequent in Mexican patients with microcytosis and hypochromia. We report three novel mutations and analyze the actual mutational spectrum in Mexican population.

METHODS

One hundred and forty-nine β-thal Mexican mestizo patients were studied (154 alleles). ARMS-PCR was performed to identify Cd39C>T, IVS1:1G>A, IVS1:110G>A, -28A>C, initiation codonA>G and IVS1:5G>A mutations, and gap-PCR for δβ-thal Spanish type. DNA sequencing of HBB gene was carried out in negative samples for the initial screening.

RESULTS

Fifteen different HBB gene mutations were observed in 148 alleles; three of them are novel: -90C>G, 20 bp deletion (at codons 78/85), and IVS2:2T>G; the mutation IVS1:6T>C that was observed for first time in our population; and eleven previously described mutations. Six alleles showed normal HBB sequence. To date, a total of 21 different mutations have been observed in Mexican patients; the four most frequent mutations are of Mediterranean origin: Cd39C>T (37.2%), IVS1:1G>A (17.3%), IVS1:110G>A (13.9%), and δβ-thal Spanish type (9.0%), which represent 77.4% of the total studied alleles.

CONCLUSION

Considering the novel mutations -90C>G, -20 bp Cd78/85, IVS2:2T>G and the first observation of IVS1:6T>C, the molecular spectrum of β-thal in Mexicans comprises 21 different mutations, confirming the high allelic heterogeneity in Mexicans.

Determination of SCN1A genetic variants in Mexican patients with refractory epilepsy and Dravet syndrome

Mutations in the SCN1A gene can result in syndromes associated with epilepsy, including the Dravet syndrome (DS). However, the prevalence of such mutations in these diseases varies widely between different studies, and has not been examined in Mexican patients with epilepsy. Therefore, the objective of this study was to determine the frequency of SCN1A mutations (in the exon 26) in a cohort of Mexican patients with DS and refractory epilepsy (RE). We recruited 24 Mexican patients (14 males and 10 females), of which 15 were diagnosed with RE and 9 were diagnosed with DS. The SCN1A gene was sequenced to uncover mutations in exon 26. We detected 2 novel genotypes in 2 DS patients. One was a synonymous variant, c.5418 G > A (E1806E), and the other was a missense variant, c. 5324 T > C (L1775P). The missense mutation was predicted to be damaging with a score of 100% by the PolyPhen-2 program. The frequency of pathogenic variants was 4.17% in all the patients and 11.1% in DS patients, which, together with other publications, emphasize that specific and more severe phenotypes are associated with SCN1A mutations.

Association between the CDH1-472delA and -160C>A polymorphisms and diffuse and intestinal gastric cancer in a Mexican population

Gastric cancer (GC), the third leading cause of cancer-related deaths in Mexico and worldwide, can be classified into diffuse (DGC) or intestinal (IGC) types based on its histological characteristics. DGC is characterized by reduced expression of the cell adhesion protein E-cadherin, which is encoded by CDH1. The -472delA (rs5030625) and -160C>A (rs16260) polymorphisms in CDH1 induce a decrease in gene transcription; in fact, these mutated alleles have been associated with GC in some populations, with conflicting results. The aim of this study was to determine the association between the CDH1 -472delA and -160C>A polymorphisms and DGC and IGC in Mexican patients. The study was conducted in 24, 23, 48, and 93 individuals with DGC and IGC, without GC (control), and belonging to the general Mexican population (GMP), respectively. The genotypes were obtained by polymerase chain reaction - restriction fragment length polymorphism and the obtained data analyzed using Arlequin 3.1. The frequencies of the mutated allele (A) of -472delA were 0.326, 0.318, 0.284, and 0.296 in the DGC, IGC, control, and GMP groups, respectively, and those of the -160C>A polymorphism were 0.174, 0.318, 0.313, and 0.280, respectively. The genotype and allele frequencies of the two polymorphisms did not differ significantly (P > 0.05) among DGC, IGC, and control subjects. Therefore, we concluded that the CDH1 -472delA and -160C>A polymorphisms are not associated with DGC or IGC in patients from western Mexico.

Dup-24 bp in the CHIT1 Gene in Six Mexican Amerindian Populations

Chitotriosidase (CHIT, EC 3.2.1.14) is an enzyme secreted by activated macrophages with the ability to hydrolyze the chitin of pathogens. The high activity of this enzyme has been used as a secondary biomarker of response to treatment in patients with Gaucher disease (OMIM 230800). Within the world's population, approximately 6% is homozygous and 35% is heterozygous for the most common polymorphism in the CHIT1 gene, a 24-bp duplication (dup-24 bp), with homozygosity of this duplication causing inactivation of the enzyme but without major consequences for health. To determine the frequency of the dup-24 bp CHIT1 gene in indigenous populations from Mexico, 692 samples were analyzed: Purepecha (49), Tarahumara (97), Huichol (97), Mayan (139), Tenek (97), and Nahua (213). We found that the groups were in Hardy-Weinberg equilibrium. The dup-24 bp allele frequency was found to be (in order of highest to lowest) 37% (Mayan), 34% (Huichol and Nahua), 33% (Purepecha), 31% (Tenek), and 29% (Tarahumara).

EGFR gene polymorphisms -216G>T and -191C>A are risk markers for gastric cancer in Mexican population

Epidermal growth factor receptor (EGFR) is a transmembrane glycoprotein with tyrosine-kinase activity that plays an important role in multiple cellular functions. EGFR overexpression has been observed in several types of tumors and it is significantly associated with disease stage, survival, prognosis, and progression of cancer. The polymorphisms -216G>T, -191C>A, and (CA)n first intervening sequence (IVS1) have been related to EGFR overexpression and have been studied in several types of cancer, but not in gastric cancer (GC). The aim of this study was to determine the association of these 3 polymorphisms and GC. Genomic DNA from 68 GC patients and 102 healthy blood donors were analyzed. Polymorphisms were identified by DNA-sequencing (-216G>T and -191C>A) and GeneScan (CA)n IVS1. The results showed that the distribution of the -216G>T and -191C>A genotypes differed between groups (P < 0.05). The odds ratio for the -216TT genotype was 4.59 (95% confidence interval = 1.55-13.54, P < 0.05) and 10.71 (95% confidence interval = 2.31-49.59, P < 0.05) for the -191AA genotype, both in a recessive model. The genotype and allele distributions of the (CA)n IVS1 repeat was similar in both groups. In conclusion, the -216TT and -191AA genotypes and GA haplotype of the EGFR gene were found to be associated with an increased risk of gastric cancer in a Mexican population.