My 12 Yo Son Has Just Been Diagnosed With Ehler's

My 12 yo son has just been diagnosed with Ehler's Danlos (EDS Type 3), and we are suspicious that his sister has it as well. She has been fighting intestinal polyps since she was 5 years old (actually before, but that is when we found out what was causing her bleeding). They say they are having a very hard time "naming" her polyps, and I'm wondering if there is any evidence that intestinal polyps might be caused by an underlying case of EDS?