By the year 2000, the number of women dying from COPD had surpassed the number of men. But the rising number of cases in women has not been matched by medical understanding of the disease’s apparent gender bias, according to a review published in the second issue for December of the American Journal of Respiratory and Critical Care Medicine.

Fernando Martinez, MD, professor of internal medicine at the University of Michigan, says that the disease expression of COPD in women is different than in men. “The main reason that we did this study was to highlight that there really are gender differences in the disease, and that they require additional study,” Martinez reports. Martinez is the senior author of the review.

Martinez and his colleagues assessed the state of medical and scientific knowledge on gender and COPD and found that not only are the manifestations of the disease different in men and women, but the risk factors, symptoms, disease, progression, and even diagnosis, are markedly different between the sexes.

COPD comprises what used to be considered two distinct diseases: emphysema and chronic bronchitis. Women tend to develop more airway obstruction, whereas men tend to develop a more emphysematic manifestation of the disease. Researchers are unclear as to why that is.

“It may reflect differences in exposures, or [genetic] differences in how males and females manifest damage,” said Martinez. “Or it may have nothing to do with underlying genetic differences that are gender-based.”