A new report estimates one in four North Carolinians under the age of 65 have a health condition that could lead them to be denied insurance coverage. In some counties that rate is closer to one-in-three. An advocacy group that commissioned the report calls it a compelling argument for the Affordable Care Act. Diabetes, heart disease and cancer are among the most common "pre-existing" conditions to which an insurance company might say, "No way do we want to cover you - you'll cost too much." More than 2 million North Carolinians under the age of 65 fall into that category, according to a new study from Families USA. While many of those people have insurance, they all live in fear of losing it, says Adam Linker of the North Carolina Health Access Coalition. "Again and again, the fear of being diagnosed with a pre-existing condition emerges as people's top concern in health care," says Linker. "One diagnosis can be a 'scarlet letter' that brands someone as uninsurable for life." Nikki Leahy understands that fear. Her 11-year old daughter is one of some 800,000 Mecklenburg County residents under 65 who have a pre-existing condition. Leahy's daughter was diagnosed with Type 1 diabetes three years ago - just as debate over the Affordable Care Act began in earnest. Suddenly the legislation was very important to Leahy because it prohibits insurers from denying coverage to children with pre-existing conditions. Beginning in 2014, that will also be true for adults. Leahy says her family is lucky to have good insurance now, but things can change quickly and her daughter's diabetes supplies cost thousands of dollars a year. Leahy says the Affordable Care Act gives her peace of mind to know that when her daughter is an adult, she won't be "discriminated against by an insurance company who says 'You have a pre-existing condition, we will no longer cover you.' Because for Type 1 diabetic, that would be pretty much catastrophic." The Families USA report finds Robeson County in south-central North Carolina has the highest percentage of non-elderly people with a pre-existing condition - 30 percent. Mecklenberg County is on the lower end with 23.5 percent. The national average is 25 percent.