Having Older Brothers Increases a Man's Odds of Being Gay

June 27, 2006

The number of biological older brothers a boy's mother has carried--whether they live with him in the same household or not--affects his chances of being gay. The findings, reported this week in the Proceedings of the National Academy of Sciences, by Anthony Bogaert of Brock University, lend credence to the theory that it's not the social or rearing factors that influence a man's sexual orientation, but rather prenatal mechanisms that begin in the womb. The idea that prenatal mechanisms may influence sexual orientation has been around for a couple of decades. In 1996, Bogaert along with colleague Ray Blanchard correlated sexual orientation in men with the number of older brothers, but it wasn't clear if that influence was occurring because the boys shared the same household or because they had shared the same womb.

In the new study, Bogaert pitted prenatal against postnatal by examining four samples of homosexual and heterosexual men, for a total of 944 participants. The data for three of the samples had been collected previously, and included detailed information about the men's sexual orientation, as well as their family life. Because most of the men from these three study groups came from unbroken families, Bogaert looked at a fourth group, composed of men who had been adopted or raised with half- or step-siblings. He also gathered data from this group about how long members lived with each sibling and whether they had brothers or sisters with whom they had never lived.

He reasoned that if the social or rearing factor theories were correct, he would expect to see certain things. First, it wouldn't matter whether a gay man's older brothers had been biologically related or not, the social influence would be there. Second, the amount of time the young boy lived with his older brothers, biological or not, should affect his sexual orientation. Third, if the boy did not live with older brothers, then the numbers should not impact his sexual preference. Bogaert found the opposite to be true. First, he found that only the number of biological older brothers predicted sexual orientation in men--even when the number of non-biological older brothers was significantly higher. Second, his study showed that the amount of time reared with older brothers--either related or not--did not predict a young boy's becoming homosexual. And surprisingly, Bogaert discovered that even if a young man did not grow up in the same house as his older brothers, the fact that he had older biological brothers increased his odds of being gay. The fact that the common denominator between the older and younger biological brothers is the mother hints at a prenatal influence on sexual orientation. What it could be is still a mystery. But one theory suggests that after delivering a boy, a woman's immune system produces antibodies to male-specific proteins. During subsequent pregnancies the mother's placenta may deliver the antibodies to the fetus, possibly affecting its development. --Tracy Staedter

RELATED LINKS:

By the Numbers: Gay and Lesbian Census

Do Gays Have a Choice?

Flaws in Placenta May Be Early Sign of Autism

Image: ASSOCIATED PRESS The earliest indicator yet of autism may be the presence of flawed cells in the placenta, scientists have discovered. The findings could lead to earlier diagnosis of the developmental disorder that affects approximately one in every 200 children and can result in learning difficulties, speech problems and difficulty relating to people. "The earlier we diagnose it, the more we'll understand the disease and the better and more potent our interventions may be," says research scientist Harvey Kliman of the Yale School of Medicine. Kliman and his team report their finding in the June 26 online issue of Biological Psychiatry.

The research builds on Kliman's previous work, which described abnormal, microscopic pits in the skin of the placenta. In the past, these abnormalities have been linked with a long list of genetic defects, including Down's syndrome and Turner's syndrome.

Kliman suspected that they may also be linked to autism. So in this study, he and other researchers at Yale used a microscope to examine tissue samples acquired from placenta saved by various research hospitals. Thirteen of the samples came from children later diagnosed with a form of autism; 61 samples came from children who were not diagnosed with the disease. When Kliman compared the two different kinds of tissue, he found that the placentas from the autistic children were three times more likely to have the abnormal microscopic pits. Kliman thinks that the research could lead to routine analyses of placenta from at-risk newborns, particularly those with an older brother or sister with autism. Not every autistic child may be linked to the abnormal features on the placenta. But, says Kliman, "If you do see this feature, it's unlikely that the child is completely normal." --Tracy Staedter

RELATED LINKS:

Blood Markers May Portend Autism and Mental Retardation

The Early Origins of Autism

Study Bolsters Link between Pesticides and Parkinson's

June 26, 2006

Image: ASSOCIATED PRESS People who have been exposed to pesticides are 70 percent more likely to develop Parkinson's disease than those who haven't, according to a new study. The results suggest that any pesticide exposure, whether occupationally related or not, will increase a person's risk of the disease. This means that using pesticides in the home or garden may have similarly harmful effects as working with the chemicals on a farm or as a pest controller. The research, published in the July issue of Annals of Neurology, provides the strongest evidence to date of the link between pesticide exposure and Parkinson's. The study included over 143,000 men and women who completed extensive lifestyle questionnaires beginning in 1982, and follow-up surveys through 2001. All subjects were symptom-free at the beginning of the project, when they were asked about their occupation and exposure to potentially hazardous materials. Since then, 413 of them have developed confirmed cases of Parkinson's, with a greater incidence of the disease in those who spent time around pesticides. "Low- dose pesticide exposure was associated with a significant increase in risk for Parkinson's disease," says lead author Alberto Ascherio of the Harvard School for Public Health. "I think this is one reason to be careful about using pesticides in general."

Although the causes of Parkinson's are not well understood, it has long been suspected that environmental factors play a large role. Animal studies have shown that chemical compounds commonly used as pesticides can cause a degeneration of dopamine-producing neurons. In Parkinson's, a shortage of dopamine causes the disease's characteristic motor abnormalities, including muscle tremors and muscle rigidity. Previous small-scale human studies had suggested a link between pesticides and Parkinson's, but this new study is the first to establish a clear correlation in a large patient population. The researchers also looked for links between Parkinson's and other environmental contaminants, including asbestos, coal dust, exhaust, formaldehyde and radioactive material. They found no correlation between the disease and any of the materials besides pesticides, however. Because of the design of the questionnaires, the study was not able to determine how the frequency, duration, or intensity of pesticide exposure affected the incidence of Parkinson's. The next step, according to Ascherio, is to figure out which class of chemicals is actually causing the disease, so that people can reduce their exposure. --Karen Schrock

RELATED LINKS:

New Movement in Parkinson's

Pesticides and Parkinson's

Coffee's Ties to Parkinson's