Study: Humans more diverse

Genes are more varied than scientists previously thought.
SCRIPPS HOWARD
Humans are considerably more genetically diverse than once thought, individually different not just by pairs of genes here and there, but in huge clusters of DNA segments missing or excessively duplicated across many parts of our chromosomes.
The new, more sophisticated map of human genes, published in a group of research papers recently in the journals Nature, Nature Genetics and Genome Research, suggests that the work of finding genetic causes of disease -- and related ways to diagnose and prevent or treat them -- may be more much complex than scientists thought even a few years ago.
An international team of scientists went back to a reference map for human genetic diversity -- specifically, the DNA samples of 270 individuals from Africa, Asia and North America.
New search
Previous screening had looked only at the differences in specific pairs of genes -- single base-pairs equivalent to a single letter on a written page. The new search essentially looked for differences in whole sentences, paragraphs and pages. Those differences were found in about 3,000 genes, or 10 percent of the total genes that make up a "normal" human.
The studies aren't the final word, of course. But the researchers suggest that there may be five to 10 times more variations in the genes between any two randomly chosen individuals than once thought. The earlier estimates were based on individual gene matchups that concluded all humans were 99.9 percent genetically alike.
"We need to stop thinking about people as being so genetically similar. We're really a patchwork of DNA sequences that are a lot more individualized compared to one another than we had thought," said Charles Lee, a genetic researcher at Brigham and Women's Hospital in Boston and at Harvard Medical School, one of the leaders of the project.
"Each one of us has a unique pattern of gains and losses of complete sections of DNA, and one of the real surprises of these results was just how much our DNA varies in copy number," said Dr. Matthew Hurles, a leader in research on gene-copy-number variation at the Wellcome Trust Sanger Institute in Cambridge, England.
The researchers found that, in some instances, a segment was deleted, but in other cases was copied as many as 14 times.
Links to disease
At least 285 of the 3,000 genes involved in copy variation are already linked to disease. "A recent review lists 17 conditions of the nervous system alone, including Parkinson's disease and Alzheimer's disease -- that can result from copy-number changes," Lee said.
In general, genes that are involved in the immune system and in brain development and activity -- functions that have evolved rapidly in humans -- tend to have more variation in the number of copies from person to person, the researchers found.
Genes that play a role in early development and cell division -- essential to fundamental biology -- are less likely to vary.