




Research work in the field is being done by geneticists, biologists and physicists at several universities and drug makers. The aim is to map how genes and the proteins they produce interact within cells in order to gain a better understanding of what goes wrong in the body to cause disease.






Among the findings: Deafness shared at least one of 41 genes with over 20 other diseases, suggesting that it sits centrally in a cluster of other diseases. These include cardiomyopathy, a condition in which the heart muscle deteriorates; and ectodermal dysplasia, an abnormal development of the skin, hair, nails or teeth. Colon cancer shared at least one of 34 genes with 50 other diseases. Also in the cancer cluster were squamous cell carcinoma, a type of skin cancer, and throat cancer, but these had fewer genetic links between them. The work was published in the Proceedings of the National Academy of Sciences in 2007.

Because the diseases in the cluster were linked at the level of the cellular network, "the breakdown of one gene can lead to many apparently unrelated diseases," says Dr. Barabási.

Another study by Dr. Barabási's team aimed to see if their database analysis of genetically linked diseases was borne out in real life. The researchers analyzed more than 32 million Medicare hospital claims.

When patients developed multiple conditions, they were more likely to get illnesses that had close genetic links to their original disease than they were to get other disorders.

The study, published in 2009 in one of the journals of the Public Library of Science, PLoS Computational Biology, also showed that patients who developed diseases that tend to coincide with many others were more likely to die sooner than people whose diseases were more tangentially connected.

Using the data, the researchers estimated people's likelihood of getting a second disease. A patient with ischemic heart disease, for example, has a 60% greater risk of getting Type 2 diabetes than an average healthy person.

Other biological processes also link seemingly unrelated diseases. In work published in 2008 in the Proceedings of the National Academy of Sciences, Dr. Barabási's team identified a cluster of diseases, including diabetes and anemia, or coronary heart disease and hypertension, that appear to share common metabolic pathways, such as how chemicals are broken down or used in the body.

Dr. Vidal is currently working with Dr. Barabási and other researchers to map out all the possible protein interactions within a human cell. Dr. Vidal says about 20% of the project is finished, making it already the most complete map of the human protein network. The researchers also are developing protein-network maps for other organisms, including a yeast cell and Caenorhabditis elegans, a tiny worm with some 19,000 genes, about the same number as humans.

To test the role played by key proteins, or hubs, the researchers selectively deleted proteins or genes in the organisms and observed what happened. In the yeast cell, they found only about a quarter of the genes and proteins appeared to be essential, in that they connected to large numbers of other proteins and substances. The organism died when these hubs were removed, Dr. Vidal says.

Write to Shirley S. Wang at shirley.wang@wsj.com