Behind the News: Michelle Tierney, mother

Michelle Tierney’s son, Tommy, was fine when he was born. Then, at about six months old, “he stopped responding and started to have infantile spasms”.

During a two-week stay at Our Lady’s Children’s Hospital, in Crumlin, he was diagnosed with Leigh disease, a rare disorder of the mitochondria – parts of cells that produce the energy the body needs to function. When they are faulty they cause degenerative brain and neuromuscular diseases.

Tierney was tested, too, and she now knows that she also carries the mutated gene, although without her son’s symptoms. “I was often sick as a child, and I suffer a lot with migraine, but I never got seizures like Tommy did,” she says.

Tommy, who is now almost five, uses a wheelchair, and can’t sit up, stand or crawl. “He has no co-ordination or muscle strength. He can react to what you say, but he still doesn’t have any speech.”

His mother is glad that he’s able to attend St Anne’s special-needs school in Roscrea, Co Tipperary, four days a week. “He has a very severe learning disability, but it’s good for him to go to school to mix with other children.”

Tierney, who says her only option if she wants another child is through in vitro fertilisation, using a donor egg, believes that British MPs’ approval this week of mitochondrial donation offers hope to many people in her situation.

The process involves removing a piece of DNA from a donor’s healthy egg to replace the faulty parts of an affected woman’s egg – so-called three-parent IVF – leaving the woman able to produce a healthy baby with her partner.

Dr Ellen Crushell helps families with mitochondrial diseases at the National Centre for Inherited Metabolic Disorders, at Temple Street Children’s University Hospital, in Dublin. “This development will be relevant to women who carry a mitochondrial DNA mutation and are at high risk of having a child with severe mitochondrial disease,” she says. “This gene manipulation will mean that all of their other characteristics – carried in the DNA in the cell nucleus – can be passed on while the mitochondria containing the mutated gene will be replaced by healthy mitochondria of another woman.”

Tierney, who gets help from the LauraLynn Children’s Hospice Foundation, which supports parents of children with life-limiting conditions, says it’s easy for people who aren’t affected by conditions like Tommy’s to be against the new procedure.

“I can’t have another child [at present] or get a job, because Tommy needs so much looking after. It’s like having to put your life on hold,” she says. “For so long something like this needed to happen. I don’t think it’s fair to take a risk to have a child if you’ve a high risk of passing on a condition like this. It’s no life for any child.”