Yolken believes that the retrovirus itself has to be triggered by yet another infection: a herpes virus. But Malaspina thinks the mechanism may be even stranger. Last year researchers at the Genetics Institute Inc. in Massachusetts announced that a gene carried by Yolken’s retrovirus may play an integral role in building the human placenta. The protein for which the gene codes, called syncytin, both prompts placental cells to knit together to nourish a fetus and enables the virus to fuse with the cells it infects. The source of schizophrenia, in other words, may lie far back in fetal development, perhaps in faulty neuronal wiring. “It could be that it’s a neurodevelopmental disease,” Malaspina says, “in which a flawed gene derails the normal development of brain neurons.”

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