My son Christopher was only the second ever child in this country to receive pioneering gene therapy for the life-threatening immune deficiency disorder, X-linked severe combined immunodeficiency (X-SCID). The groundbreaking treatment was developed at Great Ormond Street Hospital in London thanks to funding from the Jeans for Genes Appeal.

Diagnosed in 2001 at the age of eight months with X-SCID, an inherited condition which effectively meant he had no functioning immune system, Christopher's risk of infection was so great that he was not allowed to see other children. In fact, before the operation at Great Ormond Street, Christopher had to spend several months in a sterile isolation unit.

In December 2001, an operation carried out at Great Ormond Street introduced an artificially created gene - mixed with his bone marrow - into his body to correct the problem. Although it took a while to work, the gene therapy has now restored much of his immune system. Doctors will continue monitoring Christopher closely for years to come.

Without gene therapy, Christopher would not have lived to see his first birthday. Even if we had decided to opt for a bone marrow transplant he could have become a casualty. We have to be thankful for every day that we have Christopher.

Christopher has changed from an unsettled, shy and miserable baby into a confident and happy toddler with a wonderful sense of humour. Gone are the days of crying as soon as a stranger entered the room. Instead, we have a child full of confidence who loves nothing better than being out of doors. We know that all parents think that their child is the most wonderful in the world, but considering all that our gorgeous blond-haired, blue-eyed little boy has gone through, he has to be the biggest star of them all.

Image: Christopher Reid

The views and opinions expressed by writers herein do not necessarily reflect those of the Wellcome Trust.