Former Green Bay Packers quarterback and football Hall of Famer Brett Favre announced that he has Parkinson’s disease during a congressional hearing on Tuesday about his alleged misuse of welfare funds in Mississippi. Favre, who is 54, tied his diagnosis to multiple concussions he suffered during his football career. Research says that head injuries could be linked to the development of Parkinson’s disease and that those who play football are also more likely to develop it.

Parkinson’s disease is a degenerative and progressive condition in which parts of the brain become damaged and die, according to the National Institute of Neurological Disorders and Stroke . Neurons in the brain that produce dopamine tend to be most affected in people with Parkinson’s, which impacts a person’s ability to make smooth movements. What are the signs of Parkinson’s disease? Parkinson’s disease is known to start slowly and advance with time, although how it looks varies from person to person .

One of the most common symptoms of the disease is tremors, particularly in the hand, according to the Parkinson’s Foundation . These tremors tend to happen when your hand (or other affected muscles) are at rest. This phenomenon tends to be the first sign of the condition.

Other red flags related to Parkinson’s disease include limb rigidity and stiffness, balance trouble, posture changes, slowed movements, drooling, loss of smell and reduced blinking. Oftentimes, these symptoms start on on.