Vasectomy may be a risk factor for primary progressive aphasia (PPA), according to researchers at the Northwestern University Feinberg School of Medicine in Chicago. They believe the procedure may induce immune responses to sperm, which shares antigenic epitopes with the brain.

PPA is a neurologic disease that causes patients to lose the ability to express themselves and understand speech. It differs from Alzheimer’s disease, which impairs memory.

The researchers surveyed 47 men with PPA who were being treated at the medical school; 57 men with no cognitive impairment served as controls. All the men were 55-80 years of age. Of the nonimpaired men, 16% had undergone a vasectomy, whereas 40% of the men with PPA had had the procedure. “That’s a huge difference,” said lead investigator Sandra Weintraub, PhD, professor of psychiatry. “It doesn’t mean having a vasectomy will give you this disease, but it may increase your chances of getting it.”

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Dr. Weintraub and her colleagues, who published their findings in Cognitive and Behavioral Neurology (2006;19:190-193), also found that men who had undergone a vasectomy developed PPA at a younger mean age (58 years) than men with PPA who had not had the procedure (62 years).

In addition, they found preliminary evidence connecting fronto-temporal dementia (FTD) to vasectomy. In a smaller group of 30 men with FTD, 37% had undergone a vasectomy. The earliest symptoms of FTD are personality changes, lack of judgment, and bizarre behavior. While Alzheimer’s disease is the most common form of dementia in older men, there was no increased rate among the vasectomy patients.

Vasectomy may raise the risk of PPA and possibly FTD because the surgery breeches the blood-testis barrier, allowing semen to mix with blood. The immune system recognizes the sperm as invading foreign agents and produces antibodies in 60%-70% of men.

Dr. Weintraub said these antibodies might cross the blood-brain barrier and result in dementia. She cautioned that the “surprising” findings are preliminary. “Based on this report, the link between PPA and vasectomy is correlational.”