Lupus?

We just found out that a friend of my daughters has been diagnosed with Lupus. I understand that this is also an immune system disorder and in the same class as Crohn's. It sounds like it can range from mild to severe as well. Are Crohn's patients likely to develop this disease? Is there any connection between the two?  

  I have had ulcers since I was twelve and was always being tested for Mono.  Turned out I had both SLE and Crohn's Disease.  Both the gastro and the rhumetologist said they see this  because they are both autoimune diseases and it is not all that uncommon to have more than one autoimmune disease.  I asked, couldn't the joint pain and other Lupus symptoms be from the Crohn's and the Rhumetoligist said, yes but it's because of the SLE, you wouldn't have the high ANA with just Crohn's. 

That being said, they both said it's not uncommon but it's not common (whatever that means!)  So I wouldn't worry too much, just keep it in mind.