Lead researcher Weihong Song, a professor of psychiatry who holds a Canada Research Chair in Alzheimer's disease at the University of British Columbia in Vancouver, says the results of their study with mice found that lower oxygen levels (hypoxia) increased the activity of a specific gene.

The gene called BACE 1, encodes a protein that converts the precursor amyloid molecule to the more dangerous beta-amyloid form.

Professor Song says if blood to the brain is less oxygenated it may mean a build-up of the protein plaques that are so closely tied to Alzheimer's disease

In mice, hypoxia was found to increase amyloid plaque formation and memory loss.

The fact that lowered brain-oxygen levels, caused by reduced blood flow, increases the risk of Alzheimer's disease, is not a new theory and people who have suffered a stroke have a two or three times increased risk of dementia.

Other experts say however that the situation is far more complex and there is debate about whether the amyloid plaques cause the loss of mental function seen in Alzheimer's disease and they believe the study represents only a hypothesis rather than establishing an association.

But most are in agreement with Song that the health of the cardiovascular system is very important for the health of the brain, and the one promotes the health of the other.

Song says if blood flow to the brain can be improved, maybe the progression of Alzheimer's can be slowed down.

The study is published in the current issue of the Proceedings of the National Academy of Sciences.

Recent research has suggested that could be true for some types of kidney disease, Parkinson's disease, and Alzheimer's as well as susceptibility to AIDS.

The group found nearly 16 percent of known disease-related genes in the CNVs, including genes involved in rare genetic disorders such as DiGeorge, Angelman, Williams-Beuren, and Prader-Willi syndromes, as well as those linked with schizophrenia, cataracts, spinal muscular atrophy and atherosclerosis.

Study co-author Martin Somerville, a professor of medical genetics at the University of Alberta, discovered a connection between pinched blood vessels and missing DNA.

He found six cases where a missing strand of DNA corresponds with an identical heart condition, which he says was rather like 'a kink in a hose' of that main vessel.

The research is published in the current issue of the journal Nature.