Vasectomy dementia correlation

This press release about a possible link between vasectomy and dementia caught my eye. It just seems so, well, random.

The dementia is Primary Progressive Aphasia (PPA), a neurological disease in which people have trouble recalling and understanding words. In PPA, people lose the ability to express themselves and understand speech. It differs from typical Alzheimer's disease in which a person's memory becomes impaired.
Sandra Weintraub, principal investigator and professor of psychiatry and behavioral sciences and of neurology at Northwestern's Feinberg School of Medicine, began investigating a possible link between the surgery and PPA when one of her male patients connected the onset of his language problem at age 43 to the period after his vasectomy.
At a twice-yearly Chicago support group for PPA patients Weintraub sees from around the country, the male patient rushed into the room and asked the men sitting there, "OK, guys, how many of you have PPA?" Nine hands went up.
"How many of you had a vasectomy?" he demanded next. Eight hands shot up.

The actual association is much more slight, although highly significant in the sample. They haven't figured out a cause, but they have a hypothesis. It's the hypothesis that made the story really interesting for me, because it proposes a link between two rapidly-evolving tissue types: brain and testis:

Weintraub theorizes a vasectomy may raise the risk of PPA (and possibly FTD) because the surgery breeches the protective barrier between the blood and the testes, called the blood-testis barrier.
Certain organs - including the testes and the brain - exist in what is the equivalent of a gated community in the body. Tiny tubes within the testes (in which sperm are produced) are protected by a physical barrier of Sertoli cells. The tight connections between these cells prevent blood-borne infections and poisonous molecules from entering the semen.
After a vasectomy, however, the protective barrier is broken and semen mixes into the blood. The immune system recognizes the sperm as invading foreign agents and produces anti-sperm antibodies in 60 to 70 percent of men.
Weintraub said these antibodies might cross the blood-brain-barrier and cause damage resulting in dementia. "There are other neurological models of disease which you can use as a parallel," Weintraub said. Certain malignant tumors produce antibodies that reach the brain and cause an illness similar to encephalitis, she noted.

I suppose that if such antibodies actually do cause trouble in the brain, it is because neurons and sperm express one or more proteins in common that are rare elsewhere in the body. It seems not too surprising that two different systems closed off from the immune system might evolve to exploit similar protein networks in different ways.