Association of Helicobacter pylori cagA and Specific vacA Gene Polymorphisms with Clinical Outcome in Patients with Dyspepsia Presenting at Kenyatta National Hospital, Kenya

Abstract

Helicobacter pylori is a spiral, Gram-negative micro-aerophilic bacterium that chronically infects the gastric mucosa of more than half of all people worldwide, and is a major cause of gastritis and peptic ulcer (PU) disease, and a risk factor for gastric adenocarcinoma and mucosa-associated lymphoid tissue lymphoma. The differences in disease outcome may be the result of host factors, environmental factors and differences in the prevalence or expression of bacterial virulence factors. Cytotoxin-associated gene A (cagA) and some isoforms of vacuolating cytotoxin (vacA) gene have been associated with disease severity. The oncogenic potential of cagA is linked to its polymorphic EPIYA motifs pattern whose combinations differ geographically. The aim of this study was to establish the association of the specific virulence-associated bacterial genotypes with the clinical outcome of Helicobacter pylori infection. In this study, H. pylori strains in gastric biopsy specimens from dyspeptic patients were characterized and associated cagA, vacA gene polymorphisms and cagA EPIYA motifs pattern with the clinical outcome of infection. One hundred and twenty seven dyspeptic patients were enrolled into the study of whom 63.8% had gastritis, 13.4%, gastro oesophageal reflux disease (GERD), 11.8% non-ulcer dyspepsia (NUD), 9.4% peptic ulcer, 7.9%gastric cancer, and 0.01% other gastro duodenal diseases. H. pylori positivity was determined by histology and molecular diagnostic method directly from the gastric pathologies. The H. pylori DNA was detected in 62.99% of the one hundred and twenty seven dyspeptic patients. The prevalence of cagA gene was 48.75% among the H. pylori-positive patients. The presence of cagA was not significantly associated with the gastro duodenal diseases. The less virulent vacA alleles: m2, i2 and s2 were most occurring at 65%, 52% and 49%, respectively. The vacA allele m1, i1, and s1 were significantly associated with peptic ulcer, intestinal metaplasia and gastric cancer, all at P <0.05.There was no EPIYA ABD detected in these strains. The most occurring EPIYA pattern was the ABC (56.41%) followed by ABCC at 43% and AB at 28.21%. The presumed virulent ABCCC pattern was rare (5.13%). Increase in the number of EPIYA C repeats was insignificantly associated with peptic ulcer (p = 0.768). However, samples with more than one C repeat xiii were significantly associated with gastric cancer (OR=6.577 95% CI 1.620-26.704, p=0.008). The low prevalence of these strains might contribute to the low incidence of gastric cancer in this country. The cagA-positive H. pylori infection was averagely prevalent in dyspeptic patients in Kenya and all the CagA protein EPIYA patterns were of Western type. The less toxigenic vacA isoforms s2, m2 and i2 were highly distributed. This study confirmed the potential of vacA s1, m1 and i1 to induce gastric cancer and peptic ulcer. Further, it can be concluded that determining the EPIYA motifs in CagA protein, rather than detecting cagA gene alone, would be a better marker for assessing the risk of serious gastric pathology. The possibility of the presence of unidentified strain or certain host or environmental factors that trigger H. pylori-induced cancer and peptic ulceration cannot be ruled out.