Experts say that Ozzy Osbourne‘s singing voice could be negatively affected by his Parkinson’s disease diagnosis.

The BLACK SABBATH frontman revealed on Tuesday (January 21) in an interview on “Good Morning America” that he was diagnosed with the progressive neurological condition.

Dr. Rachel Dolhun, vice president for Medical Communications at the Michael J. Fox Foundation For Parkinson’s Research, told Forbes that patients often experience difficulties with speech and swallowing while battling the disease.

She said:

“It does this by affecting the way the vocal cords and swallowing muscles actually move.”

“In people with Parkinson’s, oftentimes the voice gets much quieter. The emotion or tone is taken away. This is really a core part of Parkinson’s for a lot of people and it becomes a very difficult symptom to manage.”

John Lehr, the head of the non-profit Parkinson’s Foundation, said that that 89 percent of people with Parkinson’s experience speech or voice disorders.

“It makes just having a normal conversation, not even just singing, very difficult,” he said.