Brett Favre’s announcement that he has Parkinson’s disease is bringing renewed attention to the potential links between football and a risk of brain disease.

Mr. Favre, the former N.F.L. quarterback who fell from grace after Mississippi officials accused him of helping divert funds meant for low-income residents, announced the diagnosis before Congress.

Brett Favres Parkinsons diagnosis raises concerns about footballs link to brain disease and the risks of repeated head injuries in contact sports