They did the "gold standard" test to see if IBS is hereditary.And the answer is somewhat.Like many other problems in humans (like heart disease) the answer is that some part of the problem is genetic, but environmental factors also play a role.What they do is they collect twins. Identical and Fraternal. You look at how many pairs of twins both have it, and how many only one has it.If fully completely genetic in all cases if one identical twin has it the other one does too. IBS is not like that.But there is a difference between the Identical and Fraternal twins so genetics is part of the story. That is more often the identical twins both have it than is seen in the fraternal twins.They use this technique all the time for various diseases and disorders, so the results are pretty well understood.K.