Advanced genetic testing paves way for personalized medicine

Washington - New genetic testing methods may not only help identify the potential risk for individuals to develop certain diseases but may also open the door for more targeted therapies and management strategies, which could be of particular benefit in higher risk patient populations.

“Recent advances made in genetic mapping techniques such as the development of whole exome and genome sequencing are allowing us to better and more quickly identify hereditary diseases ranging from genodermatoses such as hidradentitis suppurativa and familial disseminated superficial actinic porokeratosis (DSAP) to a variety of cancers and other inheritable diseases,” Jorge R. Toro, M.D., said at the 90^th Atlantic Dermatological Conference in Washington. He is chief of the department of dermatology, Washington DC VA Medical Center. “These breakthrough technologies can help forge a more personalized medicine approach for our patients.”

Putting the new genetic testing technology to work, researchers recently investigated the genetic basis of DSAP, a rare genetic variant of porokeratosis, in a group of Han Chinese families with extensive pedigrees (Zhang S-Q, Jiang T, Li M, et al. Nat Genet. 2012;44(10):1156-1160). Employing whole exome sequencing, researchers were able to specifically identify mutations in the MVK (mevalonate kinase) gene responsible for the autosomal dominant disease.

According to Dr. Toro, the identification of the susceptibility gene for DSAP can help advance the understanding of the molecular pathogenesis of the disease, which could lead to more targeted therapies and treatment strategies in the future.

“This is a powerful study based on the considerably large pedigrees and the exome sequencing technique used. After you do linkage analysis, the probability of identifying a gene is considerably high, and the ascertained genetic information is very strong,” Dr. Toro says.

Evolution of techniques

Gene testing has undergone significant evolution, progressing from single variant, full sequence of individual genes, and selected gene panel, to the now increasingly popular whole exome sequencing and whole genome sequencing techniques.

Whole exome sequencing involves capturing the exons using array-based or liquid-phase hybridization (using DNA or RNA), and sequencing using next-generation technology. According to Dr. Toro, ideal candidates for whole exome sequencing would be those patients in whom individual gene tests and targeted gene panels are negative, with no molecular basis identified, and/or in those patients with a clinical phenotype of a disease that could be explained by one of many genes.

“The whole exome sequencing technique allows you to generate a massive amount of data, which needs to be filtered to find potential ‘smoking guns.’ In many cases, the novel technique can help further elucidate the genetic basis of a disease,” Dr. Toro says.

Patients who request gene testing typically undergo an extensive diagnostic odyssey, he says, and whole exome and whole genome sequencing could facilitate the search for the responsible gene of the disease investigated. Moreover, these newer techniques also offer much more efficient, cost-effective and less time-consuming testing options when performing gene mapping.

Wealth of information

When looking for a specific condition or disease, Dr. Toro says that a single gene mapping approach could prove to be the appropriate testing technique. However, whole exome or whole genome testing approaches using next-generation technology could be ideal for more complex diseases, as these techniques enable the evaluation of millions of sequences concurrently.

“Whole exome and whole genome sequencing will typically give you a wealth of genetic information that may be associated with the investigated condition or disease. The tests may also give you other genetic data such as information regarding BRCA1 or BRCA2 gene mutations, which are associated with a higher risk for developing breast and ovarian cancers,” Dr. Toro says.

According to Dr. Toro, whole genome sequencing in particular represents a very real view into the future of genetic testing and what personalized medicine will look like. The fledgling technique allows one to look at coding sequences of an individual’s genome.

“Whole genome testing personifies the true meaning of personalized medicine. It allows you to look at the changes occurring in the chromosomes of an individual, and these changes as they relate to a condition or disease are going to indicate whether one should proceed with precautionary measures such as the surveillance of certain diseases, drug therapy and prevention surgery,” Dr. Toro says.

Disclosures: Dr. Toro reports no relevant financial interests.