Is there a genetic link between endometriosis and the brain?

FEW PEOPLE want to talk about women’s periods. The reluctance to speak plainly about “that time of the month” might explain why some gynaecological conditions are often undiagnosed. Take endometriosis, a chronic disease that causes period pain and excessive bleeding. The condition is common and debilitating: around 10% of women of reproductive age have it. Many wait ten years for a diagnosis. One study in Australia found that, on average, patients with endometriosis used 60% of their statutory sick leave to cope with the symptoms. Yet funding for research is surprisingly low, given the disease’s heavy toll.

Scientists have little understanding of what causes endometriosis and how to cure it. Doctors have noted that patients with the condition tend to suffer from other ailments, including migraines and mental disorders, but these links are still poorly understood. Scientists had long assumed that women with endometriosis were depressed because they suffered from chronic pain. But a study published in JAMA, an academic journal, argues that this is not the entire story: patients with endometriosis are more likely to have mental disorders even when accounting for pain, age and other confounding factors (see chart). Why?