Stuttering has been documented since biblical times and blamed on everything from poor parenting to demonic possession. But emerging evidence points the finger at genetics.

"Half of the people who come to stuttering therapy have a family history of the disorder," says Dennis Drayna of the National Institutes of Health. Drayna recently lead a study that – for the first time – pinpointed a set of genetic mutations associated with stuttering.

He hopes the research will help reduce stigma and alleviate the misconception it's a social problem. "Our findings clearly demonstrate that stuttering is a biological disorder," he says.