In a world first, an Irish couple whose child has a rare genetic disease are now expecting a baby unaffected by the same condition as a result of the fertility procedure, pre-implantation genetic diagnosis (PGD).

The couple, who were treated at the Cork Fertility Centre - one of only two fertility centres in Ireland licensed to carry out PGD - have a daughter with the rare disease, mucolipidosis. This is an inherited metabolic disorder which results in growth stopping around the age of two.

Most of those affected do not live beyond early childhood.

In this case, the couple are both carriers of a mutation affecting the mucolipidosis gene. Without PGD, they had a one-in-four chance of having another baby with the condition.

PGD involves one extra step within the IVF (in vitro fertililisation) process. With IVF, a woman's eggs are fertilised with sperm outside the body in a test tube and then placed back inside her womb. With PGD, following egg collection, these eggs are fertilised to produce pre-implantation embryos, which are cultured and monitored for progression.

After five days, embryos which appear to be developing normally are biopsied, which involves the removal of several cells. These cells are then analysed for specific genetic abnormalities before the embryo is transferred into the womb. Embryos that are free from a specific disorder are considered safe to be used.

At the Cork Fertility Centre, PGD is only available to people at risk of passing on certain life-limiting and debilitating conditions. These include cystic fibrosis, muscular dystrophy and fragile X syndrome.

In this case, doctors used PGD with a new technique known as karyomapping, and the couple in question are now expecting a child next month who will not be affected by mucolipidosis.

Karyomapping is a technique that has ‘transformed the field of PGD due to its rapid and robust method of detecting a wide range of genetic diseases in embryos', the Cork Fertility Centre said.

This is the first reported case in the world where PGD with karyomapping has been used in the case of mucolipidosis.

"The success of our PGD programme has been really encouraging. Until very recently, couples had to travel abroad for PGD, adding stress and expense to an already demanding process. We are delighted to say that one of our couples is expecting a baby unaffected by mucolipidosis, which the couple were at high risk of transmitting," commented Dr John Waterstone, medical director at the Cork Fertility Centre.

Last July, Lisa Cooke and Patrick Mullane from Cork became the first couple to have a baby born as a result of PGD carried out in Ireland. They underwent PGD at the Cork Fertility Centre to try to prevent their child from inheriting cystic fibrosis. Their baby, who does not have cystic fibrosis, is now eight months old.

Since then, almost 70% of couples who have undergone PGD at the Cork centre have become pregnant.

"This is a very promising success rate for this highly complex IVF treatment. We hope that these couples will be the first of many to avoid passing on inherited conditions as a result of PGD," Dr Waterstone said.

The news was welcomed by Anne Lawlor of the Genetic and Rare Disorders Organisation ahead of Rare Diseases Day (February 28).

"An estimated 300,000 Irish people will be affected by a rare disease in their lifetime, 80% of which are genetic in origin. Progress in medical research is resulting in more options becoming available, allowing those with genetic conditions in their families to make informed decisions on future healthcare options, both for themselves and for their families," she said.

For more information on PGD, see our past feature here

For more information on pregnancy, see our Pregnancy Clinic here