A couple in Colorado, United States, has used in vitro fertilisation and preimplantation genetics to produce embryos and have them screened for a child who could be a stem cell and bone marrow donor for their daughter.

The case, which has provoked widespread discussion about the ethical issues involved, is believed to be the first known instance where preimplantation genetics was used both to screen for a disease and to ensure a tissue donor match in a sibling.

The couple's daughter, 6 year old Molly Nash, was born with Fanconi's anaemia. Fanconi's anaemia is a rare, autosomal recessive disease …