A Brisbane grandmother has been charged with the murder of her autistic son who disappeared almost 50 years ago.

Maureen Enright was arrested after police received new information in August about her son Peter's disappearance.

Peter was born on 17th of June 1964 and is one of 11 children to Maureen and Michael Enright.

Peter was never reported missing, but detectives believe he disappeared between 1968 and 69, making him three to four years old at the time.

Homicide Detective Inspector Damien Hansen said that forensic officers are using ground-penetrating radar at the property.

"We are searching for remains," he said.

"We are optimistic at this stage but that will be dependent on a lot of environmental factors".