A mother who killed her disabled son because of concerns over his "pedophillic tendencies" and his vow to take his own life did so out of her great love for him, a judge has said.

Kim Margaret Earle, 49, sobbed and shook as she was sentenced on Tuesday in the Brisbane Supreme Court, which heard she was of diminished responsibility when she killed her 18-year-old Brandon on the Gold Coast in 2013.

Credit:Tamara Voninski

Justice Roslyn Atkinson said Brandon's interest in sadomasochism and child porn had reached the point where he wanted to kill himself following his arrest for child pornography offences and his mother couldn't see any way out.

"Essentially, you helped him to die out of your great love for him," Justice Roslyn Atkinson said as she sentenced Earle.