With genetic scientific advances reported almost daily, it sometimes seems as if we are merely waiting for researchers to discover the gene at fault for every human disease. The complex genetic basis of many common diseases, however, complicates prediction, diagnosis and treatment.
The Wellcome Trust Case Control Consortium (WTCCC), a constellation of more than 50 British research groups, took on the mammoth challenge of ferreting out the causes of diseases in which multiple genes are implicated. Last June they reported the findings of a study that scanned for specific gene variations among 17,000 British citizens: 2,000 each from patient groups diagnosed with bipolar disorder, coronary heart disease, Crohn's disease, rheumatoid arthritis, hypertension and diabetes types 1 and 2, as well as 3,000 unafflicted who served as a control group. The large scale of the study was unprecedented and so was the payoff: 24 locations in the genome were found to be associated with six of the seven diseases.
The WTCCC compared the genomes of each affected group with those of the controls and zeroed in on locations where DNA bases differed between the two groups. The size of the study was essential in enabling the researchers to spot rare anomalies. Some of the signals were in coding regions of genes; some were in noncoding regions that might regulate other genes; and some were in “gene deserts”—noncoding regions with no identified function. The variants themselves may not actually be responsible for the diseases. But they serve as signposts for other researchers to investigate DNA at a fine scale.
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Every person possesses a certain pattern of “polymorphisms” in the six billion nucleotides of their genomic DNA—three billion for each of the two sets of chromosomes. The statistical pattern of how these variations occur, provided by studies such as the one conducted by the WTCCC, will help physicians calculate the chances that a patient could develop symptoms of a hereditary disorder. The ultimate goal of this research is personalized medicine in which patients submit a blood sample and have their entire set of genes analyzed to determine predisposition to chronic diseases, the best food and exercise regimens to stay healthy, and which drugs and dosages will be most effective when illness does strike.
GENOME-WIDE SCANS turned up gene variants associated with disease, such as those for type 1 diabetes, shown as green highlights on a representation of chromosomes.
