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Down syndrome cells in the brains of healthy people may play a role in Alzheimer's disease

1 September 2009

BioNews reporting from the British Society for Human Genetics (BSHG) annual conference in Warwick:

The presence of Down's syndrome cells, characterised by an extra chromosome21 may play a role in the development of Alzheimer's disease in healthy people. Furthermore, it is possible that we are all Down's syndrome mosaics, having different proportion of trisomy 21 cells in different parts of our bodies, according to Maj Hultén, Professor of Reproductive Genetics at Warwick University, who is chairing a session covering this topic at the British Society for Human Genetics annual conference.

Building on previous work indicating that varying proportions of so-called 'trisomy 21' cells are present in the ovaries of all women from birth, Professor Hultén and her colleagues are now planning a study on the extent to which these cells are present in different tissues and how this might relate to common diseases, such as childhood leukemia and Alzheimer's disease.

Dr Kevin Moffat, who is co-leading the research, said: 'A number of susceptibility genes which lead to early-onset Alzheimer's have now been discovered. Additionally, only one gene has been associated with the more common sporadic form of the disease. While it seems likely that more will be uncovered through genome wide association studies, chromosomal mosaicism in the brain may also have a role. Down's syndrome patients surviving beyond 40 years of age often develop Alzheimer's disease due to the presence of trisomy 21 cells in their brains. We are currently planning a study to determine whether an increase in trisomy 21 cells in the brains of normal individuals is likely to play a major role in the origin of Alzheimer's disease.

In a study published in Molecular Cytogenetics last year, Professor Hultén and colleagues studied the ovaries of eight normal female fetuses, which has been aborted for social reasons and obtained with informed consent from the mother. The ovaries of all eight of the foetuses were found to contain some cells carrying an extra chromosome 21, suggesting that all women may have varying degrees of so-called trisomy 21 cells in their ovaries from birth.

Professor Hultén believes that the accumulation of cells with the incorrect number of chromosomes, so-called chromosomal mosaics, in other tissue types could contribute to a number of human diseases. She said: 'Our research suggests that all women have trisomy 21 cells in their ovaries, but that the frequency varies between women, and that these cells accumulate during development from fetal life until adulthood. This is likely to be the reason why the risk of having a child with Down syndrome increases with the age of the mother. We are currently planning further studies to determine the extent of chromosomal mosaicism in other tissues, such as the blood and the brain. The proportion of Down's syndrome cells might affect the functioning of that tissue and this might give us new insights into the origin of human disease.'

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