A US woman accused of abandoning her daughter has claimed the girl she adopted in 2010 was in fact an adult suffering from dwarfism who ‘tried to kill’ the family.

Kristine Barnett and ex-husband Michael Barnett were charged with neglect after leaving Ukraine-born Natalie Grace in an apartment shortly before the family moved to Canada in 2013.

The family paid Natalie’s rent after they left the United States but otherwise broke off contact, Michael Barnett reportedly told police.

Natalie Grace allegedly smeared blood on mirrors and put chemicals in the family's coffee

Natalie is 3ft tall and has trouble walking.

In a defence echoing the 2009 horror film ‘The Orphan’, Ms Barnett, 45, says Natalie was 22-years-old when they left her behind - not nine, as court documents claim.

According to a letter from the family doctor, which Ms Barnett provided to a local TV station, Natalie’s date of birth at the time of adoption was 'clearly inaccurate'.

The letter, which Indiana University Health have not confirmed as genuine, states that she had adult teeth and had begun menstruating.

Kristine and Michael Barnett surrendered to the authorities last week

It also states that the girl had made a ‘career of perpetuating her age facade’, and was diagnosed with sociopathic personality disorder.

The Barnetts had the girl’s age legally changed from eight to 22 in 2012, making her legal date of birth September, 4 1989. Ms Barnett has told Daily Mail TV that the she had attempted to harm other members of the family whilst she was under their care.

“She was hiding knives in our couches. She was talking about [how] she was going to kill family members. She put chemicals in the coffee,” Ms Barnett said.

‘She was jumping out of moving cars. She was smearing blood on mirrors. She was doing things you could never imagine a little child doing.’

“She would stand over people in their sleep. She would be standing in the middle of the room and say ‘I’m waiting for the right time’.”

Natalie was in and out of mental health facilities, but was left in an apartment in Lafayette, Indiana in 2013 when the Barnetts moved to Canada to support their son, Jacob, in further education.

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The family are already known to the world through Jacob - a child prodigy who was the subject of a 2012 episode of ‘CBS 60 Minutes’. At the age of 12, Jacob was taking university maths classes and is currently pursuing a PhD in quantum gravity at the Perimeter Institute for Theoretical Physics.

It is not clear what happened to Natalie since she was left in Layafette, although court documents obtained by local media suggest that she was evicted from the apartment in 2014.

Mr Barnett is due to appear in court later this month.