Patty Duke
Patty Duke celebrates with her sons Mackenzie (L) and Sean Astin in in 2004 as she gets the 2,260th star on the Hollywood Walk of Fame in Los Angeles.Reuters

Patty Duke, the beloved American child actor who played her own twin on a hugely popular sitcom to later reveal her struggles with bipolar disorder, has died at the age of 69. She passed away in hospital near her home in Coeur d'Alene, Idaho, from complications of a ruptured intestine, said her husband, Michael Pearce.

Patty Duke roared into acting at the tender age of 12 in 1959 in her role as deaf and blind Helen Keller in the Broadway play The Miracle Worker. She won an Academy Award as Best Supporting Actress when the play was adapted to film in 1962.

America was truly smitten when she starred in the TV sitcom The Patty Duke Show, playing both roles of down-to-earth Brooklyn girl Patty Lane, and her worldly Scottish "identical cousin," Cathy Lane.

The series theme song ("they laugh alike, they walk alike, at times they even talk alike") is forever trapped in the minds of Americans of a certain age. But not all was bobby socks and hairbows.

Duke later revealed a painful life of parental alcoholism and abandonment by her father, manipulation by embezzling managers whom she accused of sex abuse and of plying her with drugs and alcohol, troubled marriages and several suicide attempts. One marriage lasted just 13 days. She even confessed later that The Patty Duke Show had been a struggle.

"I hated being less intelligent than I was," she later wrote. "I hated pretending I was younger than I was, I hated not being consulted about anything, having no choice in how I looked or what I wore, I hated being trapped."

But she continued to act and was eventually treated for her bipolar disorder. She became a caring spokeswoman for mental health and AIDS treatment, and for nuclear disarmament. She won three Emmy awards for TV roles, including a reprised Miracle Worker in 1979 in which she played Annie Sullivan, Helen Keller's teacher, and Helen was played by Melissa Gilbert.

Her son with actor John Astin, Sean Astin, called his mom a "tireless warrior," lauding her campaign for mental health awareness, which he wants to continue, he said on Good Day LA after her death. "I feel rock solid at this moment because I'm charged with a sense of mission for her," said the 45-year-old actor, a star of Goonies and The Lord of the Rings series (as Samwise Gamgee).

The family said in a statement: "Our beloved wife, mother, grandmother, matriarch and the exquisite artist, humanitarian, and champion for mental health, Anna Patty Duke Pearce, closed her eyes, quieted her pain and ascended to a beautiful place."