The great-granddaughter of one of Australia's most prominent artists says she is disappointed there is still no information on the whereabouts of a family heirloom she gave to the Prime Minister's Office as a gift.

Key points: Lisa Roberts donated the coin belonging to Tom Roberts but it has since disappeared

Lisa Roberts donated the coin belonging to Tom Roberts but it has since disappeared Coin allegedly handed to a prime ministerial adviser at official opening of NGA retrospective exhibition

Coin allegedly handed to a prime ministerial adviser at official opening of NGA retrospective exhibition Dr Roberts says "the value of the gift was consistently played down"

Dr Lisa Roberts donated a coin belonging to renowned Australian impressionist artist Tom Roberts, which has been handed down through her family.

It has since disappeared and Dr Roberts wants answers.

She said she would have expected officials to be in touch with her about the artefact after the story became public, but she has had no contact.

"I did actually tell the three people involved, the ones I was closely in discussion with, everything — that I was talking to the media and the police after the internal investigation turned up nothing," Dr Roberts said.

"I was hoping to continue that openness and transparency between us, but suddenly everything has shut down."

The coin was allegedly handed to a prime ministerial adviser at the official opening of the National Gallery of Australia's (NGA) major retrospective exhibition on December 2.

Dr Roberts said she entrusted Bruce Parncutt, a former president of the National Gallery of Victoria's council of trustees, with the coin.

It was enclosed in an envelope addressed to Prime Minister Malcolm Turnbull.

Mr Parncutt is alleged to have passed it to Michael Napthali, who is the adviser on arts, communications and intellectual property, to the Prime Minister.

Value of the gift 'consistently played down'

The ABC does not suggest the people involved have acted unlawfully and Dr Roberts said she is open to the possibility the coin has been lost.

"But I'd like that official, I've asked for a statutory declaration from all the people involved," Dr Roberts said.

"The thing that most upsets me is that I wasn't even told of the loss for neatly three months after the event.

"I wasn't given any acknowledgement of it being accepted and certainly the value of the gift was consistently played down by everybody I spoke with."

The ABC tried repeatedly to contact Mr Napthali and Mr Parncutt, but neither has responded.

The Prime Minister's Office told the ABC it was aware of the situation.