Maxwell Begley, 13, who lives in Oshawa, a city in southern Ontario, spends a lot of time with his grandmother, the Toronto Star reported Monday. Brenda Millson lives in Newcastle, about 10 miles away.
"It made me sick to my stomach to think that somebody hated my son that much and they didn't even know him," an emotional Karla Begley, Maxwell's mother, told the newspaper. "But they just hated him because he was different. That's the only reason they had to hate him."
The typed letter was sent in the mail. The writer said she lives in Millson's neighborhood and said Maxwell makes noises that frighten her "normal children."
"Do the right thing and move or euthanize him!!! Either way, we are ALL better off!!!" the the writer concluded, adding "Sincerely, One pissed off mother!"
Julie Smith, a Millson neighbor, said she decided to visit everyone both to let them know about the letter and to watch their reactions. She said everyone seemed genuinely horrified.
A spokesperson said Durham Region police are investigating the letter but have not yet determined if the writer broke the law.
When a news crew came to Millson's home, 120 people turned up to support her.
His family says Maxwell has limited verbal ability but can type on a computer and usually gets his point across. He loves watching the movie "Grease," often with his grandmother, and proudly wore his musician father's first Elvis suit on Halloween last year.
Karla Begley said Maxwell does not know about the letter and seems to enjoy the attention he's getting.
Jordana Brewster on Paul Walker: 'He was an enormous presence in my life'
Gal Gadot cast as Wonder Woman for 'Batman vs. Superman'