One of the first couples in the world to be allowed to create a sibling to save their sick child have said they hope the news will help other families.
Charlotte suffers from a rare form of aggressive anaemia
Charlie and Catherine Mariethoz, from Leicester, have been granted a licence from the Human Fertility and Embryology Authority to have a "designer baby" to give a genetic match for a stem cell transplant for daughter Charlotte.
The 20-month-old, who suffers from diamond blackfan anaemia, has undergone several blood transfusions and it is thought a transplant is her only hope.
Her parents said they were delighted by Thursday's news.
Mrs Mariethoz said: "This is the first step in the right direction. Obviously there is a long way to go yet.
"We hope this decision will now help other families in similar situations."
Mrs Mariethoz, who said the couple had always planned to have a brother or sister for Charlotte, insisted the IVF treatment was the only way to help her daughter.
"The next stage would be steroids but that would mean further trauma for Charlotte.
"There are still many hurdles to go over with IVF but the main thing is that we have got the licence and we don't have to go to the USA for treatment.
"The stem cells are so important for Charlotte and the sibling doesn't have to be affected."
The Mariethoz family have now set up the Charlotte Challenge Appeal to raise the thousands of pounds that could be needed for the treatment.
"It is an expensive process. It could cost up to £7,000 a go and could take as many as 10 attempts to find a match, so we are really only at the foot of the mountain.
"The stem cells could be stored forever and there are so many new things going on in that field that they could be used in different ways in the future."