When scientists first embarked on the effort to decipher human DNA more than a decade ago, the plan seemed simple: Break the code, the thinking went, and cures for cancer, Alzheimer's and other diseases wouldn't be far behind.
Today scientists have broken the code -- publishing for the first time the sequence of the 3 billion chemical letters that make up the human DNA.
But the cures are yet to come. Amid all the hoopla surrounding the historic effort, scientists are buckling down for what could be an even more important -- and tougher -- challenge: finding all the genes buried inside DNA and figuring out what they do.
"We're not home yet," says Dr. Victor A. McKusick, a genetics pioneer at the Johns Hopkins University and co-author of a paper on the genome research appearing today in the journal Science.
Until this process--known as "annotation" -- is complete, the decoded genome is little more than a dictionary without the definitions, he says.
Some scientists estimate it could take another century before they fully understand the role genes play in human disease, longevity and behavior and are able to develop new wonder drugs or therapies that repair nature's mistakes.
Out of the estimated 26,000 to 40,000 human genes, the roles of only a fraction are understood. Scientists combing through the decrypted genetic code have so far discovered about 40 genes that appear to play a role in diseases such as deafness, color blindness and muscular dystrophy. Still, cures or interventions to prevent them are a long way off.
Genes are clusters of chemical letters scattered throughout DNA that manufacture proteins and other chemicals. Proteins control the biological machinery of the body's 60 trillion cells.
"Most of biology happens at the protein level, not the DNA level," said J. Craig Venter, head of Celera Genomics, one of the two groups to decode the human genome and announce their results today.
But finding out how proteins do what they do requires untangling the complex relationship between genes and proteins in the body.
Just a decade ago, scientists thought that there were approximately 100,000 different human genes and that each was responsible for making a single protein. But as the number of human genes has dropped, that notion is quickly flying out the lab window.
Although far fewer genes exist than expected, McKusick said, the body is thought to contain as many as 1 million proteins. Scientists now think that each gene must be responsible for producing several proteins.
