Mr Altman said he gives his sister monthly financial support, pays her bills and rent, and offered to buy her a house, but that she “continues to demand more money from us”.
But Ms Altman claims her brother “groomed and manipulated” her and performed sex acts on her over several years, including “rape, sexual assault, molestation, sodomy, and battery”, according to a court filing seen by the BBC.
Ms Altman said she sustained “great bodily injury”, severe emotional distress and depression.
She added that she had incurred numerous medical bills because of medical and mental health treatment for her injuries.
In the UK, victims or alleged victims of sexual offences have a right to lifelong anonymity. The UK legislation which creates this right does not apply to people in the US.
“Over the years, we’ve tried in many ways to support Annie and help her find stability,” Mr Altman said, adding that he had taken “professional advice” on how to “be supportive” without “enabling harmful behaviours”.
“This situation causes immense pain to our entire family,” the statement added.