A family in Trollhättan in western Sweden has received permission from the authorities for the complicated procedure to pick an embryo with the right characteristics, following a change in the law two years ago.

Their sons, aged 12 and 4, suffer from a rare metabolic disorder. The elder is too ill to be treated, but it's hoped that the younger can be saved by a transplant of blood stem cells from a new sibling.

Three other Swedish families have also received permission to go through the procedure. Critics warn that the new child might suffer from psychological problems in the future.