Frequency of IL28B rs12979860 Single-Nucleotide Polymorphism Alleles in Newborn Infants and in Patients with Chronic Hepatitis C in Morocco

Introduction

Hepatitis C virus (HCV) infection is emerging as a global concern of public health affecting up to 3% of the human population with an estimated prevalence of 170 million people infected around the world (Shepard et al., 2005). About 60%-80% of individuals who are infected with HCV cannot eliminate the virus spontaneously and will develop chronic liver disease, especially cirrhosis and hepatocellular carcinoma (Bialek and Terrault, 2006; Chevaliez and Pawlotsky, 2007; McHutchison et al., 2009). Treatment with pegylated interferon-alpha (peg-IFN-a) and ribavirin is associated with many side effects and leads to sustained viral response (SVR) in only about 50% of the patients infected with HCV genotype 1% and 80% of those infected with HCV genotypes 2 or 3 (Manns et al., 2001; Fried, 2002; Hadziyannis et al., 2004; McHutchison et al., 2009). The HCV genotype is a predictive factor that is used for response to therapy in patients with chronic hepatitis C (CHC), though host factors including age, sex, race, liver fibrosis, steatosis, insulinoresistance, and obesity have also been associated with response to therapy by peg-IFN and ribavirin (Gao et al., 2004; Walsh et al., 2006). In addition, the role of host genetic factors in the treatment efficacy for CHC was suggested many years ago due to ethnic differences in treatment response. Recently, genome-wide association studies have explored this question and found single-nucleotide polymorphisms (SNPs) located upstream of Interluekin-28B (IL28B) to be associated with both spontaneous clearance and virologic response to peg-IFN and ribavirin therapy among patients with CHC (Ge et al., 2009; Suppiah et al., 2009; Tanaka et al., 2009; Thomas et al., 2009; Rauch et al., 2010; Chen et al., 2011; O'Brien et al., 2011). Several SNPs, including rs12979860, appear to be strong markers of this effect. CHC with the CC genotype of rs12979860 was more than twice as likely to respond to treatment as those who do not have this genotype (Ge et al., 2009; Thomas et al., 2009). rs12979860 C is more frequent in Asian and Caucasian populations than in African populations, in whom the response to HCV drug treatment is recognized as being relatively poorer than other ethnic groups (Ge et al., 2009; Thomas et al., 2009). In addition to viral responses during treatment, this genotype of IL28B is also correlated with the spontaneous clearance of HCV (Thomas et al., 2009). Due to its significant impact on the result of treatment, genetic testing for the SNP genotype of IL28B before deciding on treatment strategies has been proposed (Iadonato and Katze, 2009; Balagopal et al., 2010; Lin et al., 2011).

In Morocco, genotype 1 of HCV is the most frequent, and response to peg-IFN-a/ribavirin (RBV) combination therapy is around 50% (Benouda et al., 2009). Distribution of the C allele of the IL28B rs12979860 SNP varies according to ethnicity. Its frequency in Morocco is unknown. In this study, we sought to determine the allele C of the IL28B rs12979860 SNP frequency in the Moroccan population and, in parallel, in a cohort of Moroccan patients with chronic HCV infection who had been treated with peg-IFN-a/RBV therapy.

Materials and Methods

Result

In the study conducted on 100 DNA samples of Moroccan newborns, the CC genotype was identified in 55 samples. The TT genotype was found in 9 DNA samples, and the remaining 36 samples were CT heterozygous. Therefore, the rs12979860 C-allele frequency in the Moroccan population was estimated to be 73%. In the cohort of 60 adult Moroccan patients with CHC, the rs12979860 C-allele frequency was 58.3%. The CC genotype, which has been associated with spontaneous clearance of virus and better treatment response in many previous studies, was identified in 16 patients. Ten of these patients (62.5%) attained SVR. The unfavorable SNP genotype (TT) was found in six patients, and four of them were nonresponders. The remaining 38 patients were CT heterozygous, and 20 (52.6%) of them exhibited SVR.

Discussion

Accumulating epidemiological and experimental evidence suggest that human genetic factors play an essentially important role in immunodeficiency and susceptibility to infectious diseases, as seen in malaria and pulmonary tuberculosis (Allison, 2009; Casanova and Abel, 2007). In hepatitis C, several findings support the role of host genetics in the immune response, which may predict treatment response and viral clearance (Lloyd et al., 2007; Szabo and Dolganiuc, 2008). Genome-wide association studies in independent populations have confirmed that IL28B genetic variations are associated with a virologic response to peg-IFN and ribavirin therapy and spontaneous clearance of HCV (Ge et al., 2009; Thomas et al., 2009; Imazeki et al., 2010). Ge et al. identified a genetic polymorphism (rs12979860) near the IL28B gene on chromosome 19. Individuals with the CC genotype are twice as likely to respond to peg-IFN and ribavirin treatment compared with those with the TT genotype, both in patients of European origin and African-Americans (Ge et al., 2009). Thomas et al. (2009) compared the rs12979860 variation in HCV cohorts of individuals who spontaneously cleared the virus or had persistent infection, and found that patients with the CC genotype were associated with higher treatment response and were thrice more likely to clear the virus compared with patients with CT and TT genotypes of European and African origin. In addition, they analyzed the frequency of the rs12979860 C allele by genotyping 2371 individuals from 51 populations over the world and revealed a remarkable and overall tendency of allele frequencies: higher frequency in East Asia (>90%), lower frequency in Africa (<50%), and intermediate frequency in Europe (Thomas et al., 2009). This overall difference in allele frequency could explain the different frequencies in viral clearance and response to treatment in these populations.

In our study, we determined the frequency of the IL28B gene SNP rs12979860 C allele in the Moroccan population, which is 73%. This frequency is higher than in African populations and is more comparable to the Caucasian population. It was previously revealed that North-west Africans were genetically closer to Iberians and to other Europeans than to African-Americans (Bosch et al., 2000). In addition, we determined the genotypes and allele frequency of this SNP in Moroccan patients with chronic HCV infection who had been treated with peg-IFN-a/RBV combination therapy, and we compared this frequency between the two groups. In our cohort, the rs12979860 C allele frequency was 58.3%. This deficiency of C allele in the group of patients compared with the frequency in newborns could be explained by spontaneous viral clearance. The CC genotyped was indentified in 16 patients, and 10 of them (62.5%) had attained SVR. As expected, the CC genotype is more prevalent in the group with SVR compared with the group of nonresponders. This finding merits consideration for a study with a larger sample size of patients.

Conclusion

This is the first report providing genetic data related to the frequency of genetic polymorphisms of IL28B in Morocco. Our results show that the C-allele frequency of the IL28B gene SNP rs12979860 in Morocco is higher than in the African populations and is close to those of Caucasians. The distribution of this SNP distinguishes between healthy populations and patients with chronic HCV infection. The distribution of genotypes of IL28B rs12979860 in the population with chronic HCV infection with genotype 1 and with SVR and in nonresponders is similar to the data of previous reports. Due to its significant involvement in the response to treatment of CHC, genetic testing for IL28B SNP rs12979860 before antiviral therapy should be suggested.