A mother has been arrested over the deaths of her two severely disabled adult children who were originally believed to have committed suicide.

Police will allege the Gold Coast woman, 51, slowly poisoned her 18-year-old daughter and 26-year-old son over an 'extended period', Nine News reported.

The deaths occurred between September 2012 and July last year, police said.

A mother has been arrested over the deaths of her two severely disabled adult children

The daughter is believed to have been found dead at a home in Maudsland, before her brother's body was discovered at the same address nearly five years later.

The woman has been taken into custody and is expected to face Brisbane Magistrates' Court on Wednesday.

She is expected to be charged with murder later on Wednesday.

More to come.