- NEW: Casey Kasem's longtime manager said the star is still of sound mind
- Kasem's children not being allowed to see father, says his daughter Kerri
- Kasem, 81, is suffering from Parkinson's disease
- Popular radio host best known as the voice behind "American Top 40"
(CNN) -- Casey Kasem's children are being prevented from visiting their ailing father, his daughter Kerri told CNN.
Casey Kasem, known for his years hosting the countdown shows "American Top 40" and "Casey's Top 40," is suffering from Parkinson's disease. He's 81 and retired from his radio hosting in 2009.
According to Kerri Kasem, about three months ago, her stepmother, Jean Kasem, suddenly barred her sister, her uncle and some of Kasem's friends from seeing him. She's perplexed by the decision.
"I don't get it, I don't understand it," Kerri Kasem, who co-hosts the radio show "Sixx Sense" with Motley Crue's Nikki Sixx, told CNN. "He has Parkinson's and all the research we've done indicates socialization would help him."
CNN has reached out in an attempt to get a statement from Jean Kasem, but has so far been unsuccessful.
Los Angeles TV station KABC reported that Kerri Kasem and other members of the family held a protest at Kasem's Holmby Hills house on Tuesday.
"He can't really speak, but he knows we're there," she told the station. "And last time we saw him, he could shuffle a little bit. He had a hard, very hard, time walking. He was just deteriorating due to Parkinson's disease."
"We fear that he's been isolated and neglected, and so that's why we stand here today," said Gonzalo Venecia, Casey's former personal assistant.
Asked about accusations that her family was trying to become beneficiaries of Kasem's will, Kerri Kasem told CNN that wasn't the case.
"My dad told us a long time ago we were not in the will, and we're OK with that. We've known that for years," she said. "I've never asked him for anything, nor have I asked Jean for anything."
Don Pitts, Kasem's agent of more than 35 years, said he did not want to take sides in the argument, but he did say Casey is still of sound mind at age 81.
"He has Parkinson's, has it very bad. It took his speech, and for somebody who made millions of dollars using his voice -- for him to lose that gift, that beautiful instrument -- it must be frustrating. But he's handling it very well," Pitts said.
"His mind is very sharp, his brain works well. You can tell in his eyes he understands everything you're saying. He just has trouble translating it from the brain to his vocal cords."
Besides the famed countdown shows, Casey Kasem was also the voice of Shaggy in the cartoon "Scooby Doo" and an announcer for NBC. He was a popular DJ and occasional actor before "American Top 40" began in 1970.
CNN's Denise Quan contributed to this report.
