Differentiating Between Hepatitis C Genotypes and the IL-28B Genotype
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As we learn more about Hepatitis C, it becomes increasingly clear that treatment regimens need to be customized for each infected individual. Besides different strains of the virus requiring different treatment approaches, differences on the human genome add another variable to how easy or difficult it can be to defeat the Hepatitis C virus.
There are many things a physician and his or her patient must take into account when trying to decide if that person is a candidate for treatment, which combination of drugs to begin with and what length of time is ideal. Among the long list of considerations to arrive at the answers to these questions, two important issues are:
- What Hepatitis C genotype does the person have?
- What is the person’s IL-28B genotype?
Although there is some terminology shared between these two characteristics, their origins and implications for Hepatitis C treatment are distinct.
Hepatitis C Genotype
As of late 2007, there are seven known variations of the Hepatitis C virus. Known as Hepatitis C genotypes, these genetic differences are routinely tested for with every new Hepatitis C diagnosis. Although not associated with someone’s race, Hepatitis C genotypes are more common in differing locations.
- Genotypes 1, 2 and 3 – These Hepatitis C genotypes are most common in North America and Western Europe.
- Genotype 4 – Hepatitis C genotype 4 is most common in Africa, Egypt and the Middle East, but is increasingly seen in some parts of Europe.
- Genotype 5 – Hepatitis C genotype 5 is mostly seen in Africa and the Middle East.
- Genotype 6 – Hepatitis C genotype 6 is most common in Southeast Asia.
- Genotype 7 – Hepatitis C genotype 7 has primarily been encountered in Central Africa.
Of particular importance, each genotype has a different response to conventional treatment.
In order to prescribe a treatment plan with the highest chances of success, a person must have his or her particular Hepatitis C genotype identified.
IL-28B Genotype
Just like the Hepatitis C virus has its own genetic make-up, so do we. An international research effort to sequence and map all of humans’ genes – together known as the genome – was completed in April 2003. This discovery gave us the ability to read nature’s complete genetic blueprint for building a human being.
The human genome comprises a sequence of approximately three billion parts, called nucleotides, which are organized into DNA molecules. The nucleotides, which serve as the alphabet for the language of life, are represented by just four letters: A, C, G and T – corresponding to adenine, cytosine, guanine and thymine.
Research presented in 2010 revealed that the coding at a single site on the human genome made a big difference in people’s response to Hepatitis C treatment. Known as IL-28B, this site may have either a T or a C on the genome. Since a person inherits two copies of the genome (one from each parent) to make up each allele, individuals may have one of the following alleles at IL-28B:
- TT – These individuals were found to have the poorest response to Hepatitis C treatment.
- CC – These individuals have the best response to Hepatitis C treatment.
- TC – These individuals appear to have a response to Hepatitis C treatment in between those with the TT and CC alleles.
Since the C nucleotides are more common in Europeans than in Africans, it makes sense that those of European descent have a better rate of beating the virus than those of African descent.
Testing for IL-28B
A person’s genetic code at a specific spot in the genome could foretell his or her response to Hepatitis C treatment. As such, the test evaluating the IL-28B allele is gaining popularity. David King, CEO of LapCorp, singled out their IL-28B assay as partially responsible for his company’s modest growth.
At this point, many people are interested in receiving the IL-28B assay to help determine their chances for successful Hepatitis C treatment. Unfortunately, most insurance companies do not currently cover this pricey test. While several individuals have reported that some Hepatitis C clinical trials may include this test in their screening protocol, the majority of those with this virus may not be able to obtain it yet. The time needed for such a policy change within health insurance companies can be a positive or a negative.
- On the plus side, knowing your IL-28B allele combo can better guide a doctor and patient toward a custom-tailored Hepatitis C treatment regimen.
- On the other hand, revelation of a TT allele combo could be cause for an insurance company to deny treatment coverage.
Regardless of what tests are currently covered by health insurance companies, there is little doubt that Hepatitis C treatment is becoming increasingly specialized. Besides knowing the Hepatitis C genotype you are infected with, each person will eventually need to know which nucleotides are on the IL-28B segment of his or her genome. Being armed with specific genetic information about the virus and specific genetic information about the infected person will help practitioners construct the best possible Hepatitis C treatment plan for their patients.
References:
http://www.cbse.ucsc.edu/research/human_genome, What is the Human Genome?, Retrieved November 28, 2010, Center for Biomolecular Science & Engineering, 2010.
http://www.genome.gov/10001772, All About the Human Genome Project, (HGP), Retrieved November 28, 2010, National Human Genome Research Institute, 2010.
http://www.genomeweb.com/newsletter/sample?page=1, LabCorp’s Esoteric Testing Grew 7 Percent in Q3 as Total Revenues Rose 7.7 Percent, Kirell Lakhman, Retrieved November 28, 2010, GenomeWeb LLC, 2010.
http://www.hepatitis-central.com/mt/archives/2008/01/an_updated_repo.html, An Updated Report on Hepatitis C Genotypes, Nicole Cutler, L.Ac., Retrieved November 28, 2010, Natural Wellness, 2010.
http://www.hivandhepatitis.com/2010_conference/croi/docs/0312_2010_c.html, IL28B Gene Variation Linked to Spontaneous Clearance and Treatment Response in HIV/HCV Coinfected People, Liz Highleyman, Retrieved November 27, 2010, hivandhepatitis.com, 2010.
http://www.mayomedicallaboratories.com/test-catalog/Clinical+and+Interpretive/57185, Unit Code 57185: Interleukin 28B (IL28B) Polymorphism (rs12979860), Retrieved November 27, 2010, Mayo Foundation for Medical Education and Research, 2010.
http://www.natap.org/2010/HCV/062810_01.htm, Reaping the Early Harvest of the Genomics Revolution – IL28B gene predicts response to Peg/Rbv SVR in Caucasians & African-Americans-Editorial, Raymond T. Chung, Retrieved November 28, 2010, Gastroenterology, May 2010.
