Crohns and IBS occur by two very different mechanisms so I don't really see how genetically having a parent with Crohn's sets you up for IBS.HOWEVER, people with Crohn's often have functional bowel problems as well. It is reasonably common for people with Inflamatory Bowel Diseases to have symptoms during times when all indicators show that they Inflamation is under control. Some think this may be from functional problems that are caused as a fall out of having the nerves in the gut damaged by inflamation. And how much this damage effects you seems to be part of the genetic stuff with IBS. At least it is a good working theory (the more suseptible the Enteric Nervous System is to being disrupted the more likely your environment will trigger IBS)It is also possible that something psychosocial is going on in the family that adds to all the kids having more of a chance of getting IBS (like stressors from your Mom being sick, how that altered the family dynamics, etc). Or other environmental risk factors that you all had in common (like food poisoning, what particular colonic flora you all got, and sometimes IBD patients have different flora from normals because of all the inflamation and your main exposure during the time you get colonized is when you are a baby and from Mom).So there could be any number of environmental factors you have in common in addition to some genetic predisposition.K.