The presence of male DNA in female brains is fairly common, scientists have found, and likely originates from cells of a male fetus crossing into the mother during pregnancy. The implications of the phenomenon for health and disease remain uncertain.
Lead author Dr William Chan of the Fred Hutchinson Cancer Research Center, Seattle, USA, spoke of the need for further research: 'Currently, the biological significance of harbouring male DNA and male cells in the human brain requires further investigation'.
Fetal microchimerism, when cells of a fetus cross the placenta and establish themselves in the mother, has been seen in other organs. However this is the first study to report male DNA in the brains of women, suggesting that fetal cells can frequently cross the human blood-brain barrier.
The researchers studied the autopsied brains of 59 women who were 32 to 101 years old when they died. Twenty-six had no neurological disease and 33 had Alzheimer's disease. They found male DNA in 63 percent of the brains.
A slightly lower occurrence of male microchimerism was seen in the patients with Alzheimer's disease compared to those with no neurological disease. However, the researchers note that no link between Alzheimer's and microchimerism can be made, because of the small number of brains studied and the lack of information on the women's pregnancy history.
Studies of other kinds of microchimerism have linked the phenomenon to autoimmune diseases and cancer. In some instances the microchimerism is linked to a higher risk of disease and in other cases a reduced risk.
Professor Lee Nelson at the Fred Hutchinson Cancer Research Center, who led the study said: 'Better understanding of the actions of the transferred cells could someday allow clinicians to harness the stowaways' beneficial effects while limiting their destructive potential'.
This study was published in the journal PLOS One.