Scientists know this much about polycystic ovary syndrome: It is one of the most common causes of infertility. It's linked to diabetes and several other troubling health problems. It affects as many as 5 million U.S. women.

But the condition, also known as PCOS, largely remains a mystery. Researchers are trying to better understand the disorder, which is generally defined by an excess production of the hormone testosterone, irregular ovulation and cysts—fluid-filled sacs—within the ovaries. Some teams are trying to improve...