What if a blood test could reveal that your child is at high risk for early heart disease years in the future, giving you a chance to prevent it now? A big study in England did that — screening thousands of babies for inherited risk — and found it was twice as common as has been thought.The study also revealed parents who had the condition but didn't know it, and had passed it on to their children. Ninety percent of them started taking preventive medicines after finding out.Researchers say the two-generation benefits may convince more parents to agree to cholesterol testing for their kids.