Sarah Palin with her youngest son Trig during the 2008 presidential campaign

Former US vice-presidential candidate Sarah Palin has criticised TV show Family Guy for "mocking" her son who has Down's syndrome.

Palin said on Facebook that an episode in which a character with Down's said she was daughter of the ex-governor of Alaska was "a kick in the teeth".

The politician's daughter Bristol went on to say that the "insults hurt too much for us to remain silent".

The animation's creator said the show was "an equal opportunity offender".

'Heartless jerks'

"From its inception, Family Guy has used biting satire as the foundation of its humour," Seth McFarlane said in a statement to the Los Angeles Times.

Bristol Palin went on to say in the posting: "If the writers of a particularly pathetic cartoon show thought they were being clever in mocking my brother and my family yesterday, they failed.

"All they proved is that they're heartless jerks."

Her mother, who stepped down as governor of Alaska last year, said her daughter's reaction was "a much more restrained and gracious statement than I want to make".

She added that the issue "begs the question, when is enough enough"?

The episode of the animation featured Chris - the Griffin family's son - bringing home a girlfriend with Down's syndrome.

When quizzed by his parents about her family, she said that her mother used to be Alaskan governor.

The show is broadcast on the Fox network in the US.

Palin is commentator for cable station Fox News, also owned by Rupert Murdoch's News Corporation, but separate from its namesake.