The four GWAS studies found the same cluster of SNPs around IL28B, nicely cross-validating the studies. One curious statement in the N&V is
Although all of the identified variants in the three studies lie in or near the IL28B gene, none of them has an obvious effect on the function of this gene, which encodes interferon-3, a growth factor with similarities to the interferon- preparations used as treatment.
Two of the papers provide direct evidence as to at least one effect of these SNPs; one showed that the SNPs are linked to the expression of both IL28B and the nearby related gene IL28A; the other looked only at IL28B. Lower expression of these loci was correlated with the genotype with worse prognosis.
The N&V goes on with some boilerplate pessimism about GWAS studies impact on medicine
The question remains, however, as to how readily these and other observations from GWAS can be translated into meaningful changes in patient care. The field of human genetics has described many associations between specific mutations and medically important outcomes, but rarely have these observations resulted in new therapies to treat disease or in major shifts in existing treatments. This failure is exemplified by the lack of clinical benefit that followed the cloning in 1989 of the gene responsible for cystic fibrosis11 — the first example of the use of molecular genetics to discover the cause of an otherwise poorly understood condition. Although some progress has been made in treating patients with cystic fibrosis, in the ensuing 20 years neither of the two newly approved drugs for this condition were developed using knowledge of the gene mutations that cause it. Apart from a few well-characterized beneficial mutations (for example, those resulting in resistance to HIV infection), genetics has been an inefficient tool for drug discovery.. They also pile on with graphs showing the exponential growth of Genbank and dbSNP vs. the flat numbers for INDs (new drugs into trials) and NMEs (new approvals).
So although these findings raise the tantalizing prospect of a more personalized approach to treating HCV by tailoring treatment to patients who are most likely to benefit, the reality is more sobering. Diagnostic testing to identify likely responders to interferon may be a future possibility, but clinical decision-making will be clouded by the fact that the effect of the advantageous variant is not absolute — not all carriers of the variant clear the virus, nor do all patients lacking the variant fail to benefit from treatment. Furthermore, there is currently no alternative to interferon therapy for the HCV-infected population.
Of course, I could respond with the boilerplate response (found in at least one of the papers) that patients with the "poor response" genotype. And indeed, new HCV therapies are in the pipeline, perhaps most prominently a compound under development by Vertex. Understanding if these variants affect response to the new compounds now becomes an important research question.
But, it's also stunning that the N&V authors didn't suggest a rather obvious approach suggested by these papers. Not only do patients with the "high expression" genotype respond better to therapy, but this genotype also predicts spontaneous clearance of the virus. Furthermore, these loci encode secreted immune factors. So to me at least, this can be viewed as a classic protein replacement therapy candidate -- a subset of patients produce too little of a natural protein (or two natural proteins) and providing them with recombinant protein might provide therapeutic benefit. I suspect that whatever companies hold patent claims on IL28A & IL28B are contemplating just such a strategy. This is also in stark contrast to cystic fibrosis, where the affected protein is damaged rather than underexpressed and is a membrane protein not a secreted protein. By focusing on the general difficulty of converting genetic information to therapy rather than the specific circumstances of these papers, the N&V authors completely blew it.
IL28A & IL28B loci produce proteins classified as interferons and it is another interferon (alpha) which is a key part of the standard therapy. A more extreme version (or a bit of the flip side) of the protein shortage theory would posit that the sum of the interferons is important for response -- and perhaps also for side effects. If this were the case, then increasing the dose of alpha interferon in the "low expression" genotype (or better yet, actually typing patients white cells for expression of these proteins) might be a reasonable clinical approach. Given that interferon alpha is already approved, this is the sort of clinical experimentation that goes on all the time.
Yet another angle suggested by the "IL28A/B deficiency hypothesis" is that a viable therapeutic discovery approach is to find compounds which increase expression of IL28A and/or IL28B in leukocytes. This has been a successful strategy for generating new therapeutic hypotheses in oncology. Better yet, hints may already exist -- some enterprising student should search the Broad's Connection Map or other databases of expression data for cell lines treated with compounds to identify compounds which upregulate IL28A/B transcripts. A hit in such a search or a broader screen of already approved compounds could potentially rapidly lead to clinical experiments.
The one time I had an opportunity to write a N&V (as a grad student) I got writer's block and missed the boat. It will always irk me. But, perhaps it's better to blow a chance silently rather than write such an awful, unimaginative one which stuck to stock genomics negativity rather than creatively exploring the topic at hand.
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Ge, D., Fellay, J., Thompson, A., Simon, J., Shianna, K., Urban, T., Heinzen, E., Qiu, P., Bertelsen, A., Muir, A., Sulkowski, M., McHutchison, J., & Goldstein, D. (2009). Genetic variation in IL28B predicts hepatitis C treatment-induced viral clearance Nature, 461 (7262), 399-401 DOI: 10.1038/nature08309
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(ugh: had a serious typo in the title on first posting; now fixed & revised)