What else can cause extremely high triglyceride levels besides diet?

I am 30 years old and my triglyceride levels have been tested at around 1200 before medication.  I am an athlete and eat carefully but can never get rid of the fat around my gut. No one in my family has high triglycerides but almost all the males in my family die in their late 40's or early 50's of heart disease.  The only two causes I have heard are diet and genetics.  Could there be something else causing this?   My body has responded well to medication and it brought the levels back down to close to normal.  My concern is that the medication might only be masking the symptoms of another problem.  Thanks for your input.