Background/Objectives: The purpose of the current study was to compare the methylation of five regions of the CpG island of MLH1 with the presence of microsatellite instability (MSI) in colorectal cancer (CRC) patients. Methods: The study analyzed 138 CRC tumor samples. DNA extraction was performed, followed by bisulfite conversion. MLH1 gene methylation was assessed by methylation-specific PCR (MS-PCR), and the resulting fragments were analyzed using polyacrylamide gels. MSI was evaluated using multiplex PCR, and the fragments were run through capillary electrophoresis. R studio (v4.4.1) and SPSS (v29.0) software were used for the statistical analysis, and values of p < 0.05 were considered statistically significant. Results: The study showed 75.4% unmethylated, 21% partially methylated, and 3.6% fully methylated samples, with region A frequently methylated. MSI was observed in 7.2% of cases (MSI-H: 5.8%, MSI-L: 1.4%). BAT-26 was the most unstable marker. A significant difference between MLH1 methylation and MSI-H (p < 0.01) was identified, but there was no relationship with specific MLH1 regions. Conclusions: No differences were identified when analyzing specific methylation regions in relation to MSI. This study is the first to describe MSI frequency in Mexican patients regardless of age.

Background: Colorectal cancer is the second cause of death by cancer around the world. Sporadic colorectal cancer is the most frequent (75%), and it is produced by the interaction of environmental, epigenetic, and genetic factors. The accumulation of single-nucleotide variants in genes associated with cell proliferation, DNA repair, and/or apoptosis could confer a risk to cancer. The aim of this study was to analyze the gene–gene interactions among CCND2 (rs3217901), CDKN1A (rs1059234 and rs1801270), and POLD3 (rs3824999) vari- ants in Mexican patients with colorectal cancer. Methods: We collected peripheral blood samples from 185 patients with sporadic colorectal cancer before treatment and from 185 unre- lated blood donors as the reference group; all participants signed an informed consent form. DNA extraction was performed by Miller and Cetyltrimethylammonium bromide (CTAB)/ Dodecyltrimethylammonium bromide (DTAB) methods. Polymerase chain reaction– restriction fragment length polymorphism followed by polyacrylamide gel electrophoresis stained with AgNO3 methods were used to identify the variants rs3217901, rs1059234, rs1801270, and rs3824999. Odds ratio and single-nucleotide variant interaction were determined by single-locus analysis and Multifactorial Dimensionality Reduction software, respectively. Results: No association was found for CCND2 and CDKN1A variants; yet, a significant association for the GG genotype, G allele, and recessive and additive models for the POLD3 variant was observed (P < .05). The single-nucleotide variant–single-nucleotide vari- ant interaction revealed the combination rs1059234, rs3217901, and rs3824999 as the best model and the comparison showed an increased risk (P < .05). Conclusion: Single-locus and gene–gene interaction analyses disclosed that both the rs3824999 (POLD3) variant and the combination of rs3217901 (CCND2), rs1059234 (CDKN1A), and rs3824999 (POLD3) genotypes increase the risk for colorectal cancer in Mexican population.

We searched for the prevalence of actionable somatic mutations in exon 2 of the KRAS gene in western Mexican patients with CRC. Tumor tissue DNA samples from 150 patients with sporadic CRC recruited at the Civil Hospital of Guadalajara were analyzed. Mutations in exon 2 of the KRAS gene were identified using Sanger sequencing, and the data were analyzed considering clinical–pathological characteristics. Variants in codon 12 (rs121913529 G>A, G>C, and G>T) and codon 13 (rs112445441 G>A) were detected in 26 patients (with a prevalence of 17%). No significant associations were found between these variants and clinical–pathological characteristics (p > 0.05). Furthermore, a comprehensive search was carried out in PubMed/NCBI and Google for the prevalence of KRAS exon 2 mutations in Latin American populations. The 17 studies included 12,604 CRC patients, with an overall prevalence of 30% (95% CI = 0.26–0.35), although the prevalence ranged from 13 to 43% across the different data sources. Determining the variation and frequency of KRAS alleles in CRC patients will enhance their potential to receive targeted treatments and contribute to the understanding of the genomic profile of CRC.

Forensic DNA phenotyping (FDP) is an important innovation approach in forensics sciences, especially when traditional DNA profiling results are limited, mostly due to the absence of reference samples. FDP is based on the detection of genetic variants in specific genes whose function is related to pigmentation mechanisms and uses the genotypes found in the sample to determine the externally visible traits (EVT) such as the iris, hair, and skin tone or color of the individual; this prediction would help and expedite human identification processes and solve criminal cases. Several technologies have been developed to facilitate EVT prediction; however, most of them have been validated only in European populations. Implementing techniques for FDP in Latin American countries is essential given the problems of disappearance and human identification that have persisted for years. Nonetheless, scientists have a great challenge due to the admixed genetic structure of the population. This review explores the current application of FDP, emphasizing its significance, practical uses, and limitations within Latin American populations.

Background/Objectives: Colorectal cancer (CRC) represents a major public health problem in Mexico and is among the malignancies with the highest morbidity and mortality. Alterations in TP53 are frequent molecular events in tumors with chromosomal instability; however, information on TP53 variants in the Mexican population, particularly in exons 4-8, remains limited. Exons 4-8 comprise the main coding region of the p53 DNA-binding domain; therefore, this study aimed to identify TP53 variants in these regions and evaluate p53 protein expression by immunohistochemistry in sporadic CRC. Methods: Tumor samples from 142 patients who underwent surgical resection without neoadjuvant treatment were analyzed. DNA was extracted from tumor tissue. TP53 exons 4-8 were amplified by polymerase chain reaction (PCR), and variants were identified by Sanger sequencing. p53 immunohistochemistry was performed in 40 tumors and 36 adjacent tissues, and nuclear expression was assessed using the Immunoreactivity Score. Results: Forty-three heterozygous variants were identified in 106/142 patients, representing 75% of the cohort. Thirty-one patients carried oncogenic variants, mainly clustered within the DNA-binding domain and involving hotspot residues such as Arg175, Tyr220, Gly245, Arg248, Arg273, and Arg282. Nuclear p53 expression was observed in 9/40 tumors, whereas all adjacent tissues were negative. Conclusions: TP53 alterations in exons 4-8 are frequent and heterogeneous in this Mexican cohort. Integrating mutational profiling with p53 immunohistochemistry provides complementary information for the biological interpretation of these tumors, including variants of translational interest.

Imagina que el material genético (ADN) del que estamos hechos todos los humanos es un libro de instrucciones, donde su texto nunca cambio a lo largo de la vida, pero sí los signos de puntuación, estos signos de puntuación son la “epigenética” y un ejemplo de ésta es la metilación del ADN. La metilación del ADN es un mecanismo clave en los procesos de regulación de esas instrucciones de la vida que conocemos como “genes”. Lo interesante es que, la metilación del ADN puede cambiar a lo largo de la vida de forma predecible, permitiendo calcular la edad de una persona cuando se estudian muestras ADN provenientes de tejidos como sangre, huesos y dientes. En los últimos años, este tipo de análisis ha sido clave para la resolución de problemas forenses por su efectividad como predictores de edad. En este artículo explicaremos brevemente qué es la metilación, cómo influye en el envejecimiento y su utilidad en identificación humana y casos forenses.