Nail biters = pathologic groomers.
A new version of the American Psychiatric Association's Diagnostic and Statistical Manual of Mental Disorders (DSM) coming out early next year puts pathological grooming in that same category as OCD.
Nail biting seems to run in families - whether it's simply learned behavior picked up by watching a parent or a sibling with a digit in their mouth or something genetic or a combo of both isn't clear. It runs in my family. Myself and my son, one of my sister's and an Uncle - that I'm aware of. I guess it could be said that my son and I are more prone to compulsive behavior than the other half of my immediate family. However, my husband should really get labeled as a compulsive groomer as he showers a lot.