A new genetic map written by an international research team has forced a fundamental rethink of how genes work and has already made a difference in diagnosing some genetic diseases.

Stephen Scherer, a geneticist at the University of Toronto and the Hospital for Sick Children, and his colleagues found several hundred unusual mutations in a newly updated map of the human genome.

Geneticist Stephen Scherer: 'Now we know that our genomes are much more variable.'
(CBC)

The map was drawn up by analyzing DNA from 270 individuals from four populations with ancestry in Europe, Africa or Asia.

"Now we know that our genomes are much more variable," said Scherer, whose study is in Thursday's issue of the journal Nature. "It changes the design of all of our studies. It really changes our understanding of ourselves in fact."

The results of the study mean people are far more genetically variable than first thought. The new map shows genes don't always line up as expected — there can be mismatches, or chunks with missing or extra DNA.

The mismatched genes and rogue chunks of DNA can cause profound and mysterious health problems that could explain some forms of autism, heart defects and Alzheimer's disease, researchers say.

Genes usually occur in two copies, with one inherited from each parent. The researchers found about 2,900 genes, or more than 10 per cent of the human genome, had variations in the number of copies of specific DNA segments.

Until now, research on genetic diseases has focused on small changes called single nucleotide polymorphisms, or SNPs.

It may be that some diseases are instead caused by differences in the number of copies, and recent research suggests that's true for some types of kidney disease, Parkinson's disease, Alzheimer's and susceptibility to AIDS.

Scherer's lab discovered a connection between pinched blood vessels and missing DNA.

'Like a kink in a hose'

Study co-author Martin Somerville, a professor of medical genetics at the University of Alberta, found six cases where a missing strand of DNA corresponds with an identical heart condition.

"It's like a kink in a hose in a way of that main vessel," said Somerville.

Heath MacNaughton of Edmonton was born on Oct. 16 with a faulty blood vessel leading from his heart. A DNA test pinned the cause on the newly discovered genetic mutation.

Heath MacNaughton was born with a heart defect caused by a newly discovered genetic mutation. It can be repaired with surgery, but other conditions will be more difficult to treat.
(CBC)

The child's parents are relieved to know what caused the heart defect, but now they worry because his father passed on the mutation.

"They'll be obviously following up if there's anymore children 'cause I guess there's a pretty good chance that our next child can have the problem as well," said Heath's mother, Leigh-Ann Cullinan.

In Heath's case, the heart defect can be repaired with surgery, but other conditions will be more difficult to treat. Drugs could be used to enhance or turn down the signals coming from some genes, although the science is in its infancy.

"We can't move towards therapy unless we can find the cause, so this is obviously the first step in that process," Somerville said.

It's still early to know what the differences mean, Scherer acknowledged. "Though it does make you wonder, 'If you have one million fewer nucleotides than your buddy, shouldn't you get a break on your golf handicap?'"