Why are we studying twins?
We are studying twins because twins share either 100% of their genes (identical twins) or 50% of their genes (fraternal twins). By looking at the concordance rates for PCOS among twins (when both twins in a pair have the disease), we can tell how much of the disease is hereditary and how much is environmental. For example, if identical twins are concordant for PCOS more often than fraternal twins, this is a good indication that genetics play a larger role in developing PCOS. On the other hand, if identical twins are concordant at about the same rate as fraternal twins, then genetics and the environment might have more equivalent roles.
Also, by comparing the environments of identical twins who are discordant for PCOS (only one twin in the pair has the disease), we might be able to uncover what environmental factor triggered that twin in the pair to develop PCOS. In future studies, we hope to monitor discordant twin pairs over time for PCOS. This is very powerful as it allows us to detect new cases of PCOS as they occur, and more readily identify the environmental triggers. The same is true for the secondary conditions that women with PCOS often develop, such as diabetes or heart disease. If we can identify new cases of diabetes among twins with PCOS, we might be able to determine what triggered them to develop diabetes.