I found out that my sons great aunty has tested positive for a genetic disease that can cause multiple tumors that sometimes turn malignant and overstimulate the adrenal gland causing heart problems.

She told me this information so that I can get my two year old son checked for this disease and has asked me not to tell my sons father who is not currently a part of my sons life. His mother knows about the disease but has chosen not to tell him.

Even if my son tests negative (the tests are in progress and will be ready in about 4 months) it does not rule out his dad as being a carrier. I have trouble sleeping at night keeping this from my sons dad when I could email him and let him know about this, but if I do it will cause serious conflict in the family in that my sons dad might resent his mother for not telling him and he is already estranged from his own dad and he will disown his great aunty for speaking to me because he strongly resents me for having his child. Considering what might happen if he does have the disease and it is misdiagnosed I think it is worth the possible turmoil it will cause within the family. Just wanted to hear other peoples thoughts cos I feel so alone and I am very stressed about all this. Thank you

This is information that needs to be shared. Whatever upset it causes, so be it.

ok hon, take your time and i will check back.

What does your "gut" tell you to do? It rarely leads you wrong.
Sometimes it's hard to do the right thing in the face of others who have NOT done the right thing and will be angry. Honestly, I'm shocked that his family said nothing to your ex., especially if this is a life-threatening condition.
Do you have any clue as to why they withheld this information?
Please keep us posted.

Yes, deary, take your time. We are all here for you.

that is a very big thing to have lumped on you shoulders jesspants, if nothing else, doesnt it serve to point out how sad it is when people have animosity and anger involved within relationships, I agree with most of the above answers, if its life threatening, then your ex most likely should know, why his family havent told him themselves is quite beyond comprehension. Do they not love him?
Why dont you wait for your results to come back, then discuss the options with your own medical doctor, and ask his suggestion on the problem as well.

and yes, finally, your gut feelings are most often right.

good luck, :)