Epigenetics could explain some Moroccan population colorectal cancers peculiarities: microsatellite instability pathway exploration

A Review of Cancer Genetics and Genomics Studies in Africa

Cancer is the second leading cause of death globally and is projected to overtake infectious disease as the leading cause of mortality in Africa within the next two decades. Cancer is a group of genomic diseases that presents with intra- and inter-population unique phenotypes, with Black populations having the burden of morbidity and mortality for most types. At large, the prevention and treatment of cancers have been propelled by the understanding of the genetic make-up of the disease of mostly non-African populations. By the same token, there is a wide knowledge gap in understanding the underlying genetic causes of, and genomic alterations associated with, cancer among black Africans. Accordingly, we performed a review of the literature to survey existing studies on cancer genetics/genomics and curated findings pertaining to publications across multiple cancer types conducted on African populations. We used PubMed MeSH terms to retrieve the relevant publications from 1990 to December 2019. The metadata of these publications were extracted using R text mining packages: RISmed and Pubmed.mineR. The data showed that only 0.329% of cancer publications globally were on Africa, and only 0.016% were on cancer genetics/genomics from Africa. Although the most prevalent cancers in Africa are cancers of the breast, cervix, uterus, and prostate, publications representing breast, colorectal, liver, and blood cancers were the most frequent in our review. The most frequently reported cancer genes were BRCA1, BRCA2, and TP53. Next, the genes reported in the reviewed publications’ abstracts were extracted and annotated into three gene ontology classes. Genes in the cellular component class were mostly associated with cell part and organelle part, while those in biological process and molecular function classes were mainly associated with cell process, biological regulation, and binding, and catalytic activity, respectively. Overall, this review highlights the paucity of research on cancer genomics on African populations, identified gaps, and discussed the need for concerted efforts to encourage more research on cancer genomics in Africa.

The First Molecular Screening of MLH1 and MSH2 Genes in Moroccan Colorectal Cancer Patients Shows a Relatively High Mutational Prevalence

INTRODUCTION

Lynch syndrome (LS) is an autosomal dominant disorder characterized by early age of onset and increased risk of developing extracolonic tumors. Molecular diagnosis of LS requires identification of germline mutations in one of the Mismatch Repair (MMR) genes.

AIM

The objective of the study was to investigate the prevalence of MLH1/MSH2 mutation carriers among Moroccan patients with colorectal cancer (CRC) in a hospital-based cohort.

METHODS

In this study, 214 CRC patients from COLORECFez cohort were included. Patients whose tumors showed MMR deficiency (MMR-D) and wild-type BRAF were selected to undergo mutational analysis of the MLH1 and MSH2 genes using Sanger sequencing.

RESULTS

A total of 24 MMR-D tumors were identified (11.2%) among 214 CRC tested for MMR protein expression. The BRAF p.Val600Glu mutation was absent in all tumors deficient for MLH1 protein. Molecular screening showed germline MMR mutations (MLH1/MSH2) in four cases, two of which fulfilled Amsterdam criteria II and two met at least one of the revised Bethesda guidelines. The estimated frequency of MLH1/MSH2 mutations in Moroccan CRC patients was 1.87%.

CONCLUSIONS

The present study reports a relatively high incidence of MLH1/MSH2 (1.87%). These results confirm the contribution of MMR genes to CRC susceptibility in our population and provide evidence regarding the requirement of implementing a national screening program for LS in Morocco.