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Genetic testing: the newest preventive medicine
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 Michael D. DePaolis |
Undoubtedly, the Human Genome Project is one of modern medicine’s greatest accomplishments. With it has come a better understanding of the genetic “roots” of certain disease processes and the inherent predisposition of some individuals to those maladies. What we have also learned is not all patients are “programmed” to respond similarly to a given pharmacologic intervention.
While this does not seem particularly profound – we routinely witness variable responses among patients to the same drug – it is especially important as it relates to adverse drug reactions. Particularly, when those drug reactions can be fatal.
Carbamazepine and Stevens-Johnson syndrome
Consider carbamazepine, for instance. Carbamazepine, otherwise known as Tegretol (Novartis), is a drug with which we are all familiar. Originally developed to treat epilepsy, carbamazepine has found widespread acceptance in treating certain manic-depressive states (bipolar disorder) as well as in managing chronic pain conditions (trigeminal neuralgia, post-herpetic neuralgia, diabetic neuropathy, etc). It is an effective medication for a variety of diseases.
Unfortunately, it can also result in Stevens-Johnson syndrome. If you have seen your share of the epidermal necrotizing ravages of Stevens-Johnson, you would agree it is a condition to be avoided at all cost.
In the March 24 issue of the New England Journal of Medicine, two articles detailed the relationship between carbamazepine and Stevens-Johnson syndrome. One study looked at 22 cases of carbamazepine-induced Stevens-Johnson in people of European ancestry, along with a control population, and identified an HLA allele that confers a 25-fold increased risk of developing this dreaded side effect.
The other study, conducted in Taiwan, identified another HLA allele resulting in a predisposition towards Stevens-Johnson in individuals of Asian ancestry. In fact, the Taiwanese results were so compelling that every hospital there now performs obligatory genotype testing prior to prescribing carbamazepine.
Routine genetic testing in the U.S.
Certainly, the carbamazepine story exemplifies the power and the good of human genomics. As we have seen in Taiwan, it underscores the practical implications of genomics. Why, then, haven’t we adopted a similar policy in the U.S.? Well, the answer is not so easy.
Some argue our country is far too genetically diverse to be conducive to this type of allele-specific testing. Others say such testing invades privacy – that it might uncover other susceptibilities, resulting in health insurance denial and discrimination. Finally, there are those who argue it is cost prohibitive, citing examples where insurers simply do not cover such testing.
While each argument warrants consideration, the latter is indefensible. In a country where we consider our health care system to be world class and where we preach preventive medicine, how can we not embrace such testing? I cannot conceive of a situation in which sacrificing a few souls to Stevens-Johnson to save a buck is good policy. Again, you need only see one of these patients to recognize it must be avoided … at all cost.
References:
- Chen P, Lin J-J, Lu C-S, et al. Carbamazepine-induced toxic effects and HLA-B*1502 screening in Taiwan. N Engl J Med. 2011:364:1126-1133.
- McCormack M, Alfirevic A, Bourgeois S, et al. HLA-A*3101 and carbamazepine-induced hypersensitivity reactions in Europeans. N Engl J Med. 2011;364:1134-1143.