PARIS, Jan 18 (AFP) - Scientists believe they have pinpointed a tiny genetic flaw that is to blame for around four percent of all cases of Parkinson's, a discovery that could eventually open the way, albeit controversially, to genetic testing for the disease.
The problem lies with a single mutation in a gene called LRRK2, according to three studies published online Tuesday by the British medical publication The Lancet.
Researchers spotted the flaw by scanning and comparing the DNA of individuals with Parkinson's.
LRRK2 is a recently discovered gene which encodes for a large protein called dardarin whose function is unclear.
Two of the studies found the mutation among four out of 61 Italian, Brazilian and Portuguese families with a history of Parkinson's and among 35 individuals from 20 North American families where the disease had also struck.
The LRRK2 flaw causes around five percent of inherited cases of Parkinson's, according to an extrapolation of these figures.
However, the real proportion "is probably substantially higher," said William Nichols, of the Cincinnati Children's Hospital Medical Centre, who lead-authored the North American study.
"Mutations in this gene could become the most important cause of disease susceptibility for Parkinson's disease identified so far."
The third study was conducted among British patients with Parkinson's who did not have a family history of the disease.
In this research, the gene flaw was spotted in eight out of 482 patients, a rate of 1.6 percent, which suggests that the mutation can also occur sporadically.
Cases classified as sporadic have no inherited cause. Exposure to harmful chemicals, radiation or some other environmental factor are the usual chief suspects.
In a commentary, also published by The Lancet, specialist Alexis Brice of France's National Institute for Health and Medical Research (INSERM) said the findings were a step towards the eventual introduction of genetic tests to predict susceptibility to Parkinson's.
But, he said, it was vital to gain as complete a picture as possible about the genetic causes for the disease -- whether, for instance, people with the mutated LRRK2 gene did not develop Parkinson's and if other faulty genes might also be implicated with the disease.
In addition, it was vital to address ethical issues, Brice stressed. Parkinson's is degenerative and incurable, although its symptoms can be eased with drugs. So testing for the diseases would offer no direct medical benefit, he said.
Parkinson's is a degenerative disease of the nervous system, affecting more than one percent of people over the age of 65.
It occurs when there is a loss of cells in a part of the brain that produces dopamine, a neurotransmitter that communicates with other brain cells which regulate motor functions. Symptoms range from tremors and awkwardness and muscular stiffness to a distinctive shuffling gait.
Well-known sufferers include Pope John Paul II and the actor Michael J. Fox.
01/17/2005 19:24 GMT - AFP