British fertility specialists have developed a powerful new way to test embryos for inherited diseases, offering hundreds of couples their first realistic chance of having healthy children. The procedure has been hailed as a big advance, boosting the number of diseases clinics can test for from about 200 to nearly 6,000.
It will allow doctors to test for the first time a vast array of inherited diseases for which the specific genetic mutation is not known, such as Duchenne's muscular dystrophy (DMD) and some forms of cystic fibrosis. Using the technique, doctors can examine every embryo created for a couple through IVF, and determine whether each is healthy and unaffected, a carrier of the disease, or destined to develop the full-blown medical condition.
Such detailed knowledge of the genetic make-up of embryos will lead to a radical shift in the way couples at risk of passing on certain diseases are treated.
Some inherited conditions, known as x-linked diseases, usually only affect males, but because the mutations that cause the diseases are unknown, clinics can only screen them out by discarding every male embryo created, even if only half are affected. The new test will allow doctors to see which male embryos are free of the disease-causing mutation, so fewer embryos will be wasted. In some cases, the test will allow doctors the controversial option of asking couples to choose the sex of the embryos that are transplanted.
"This is a big, big change in what we are going to be able to do. It changes everything," said Professor Peter Braude of King's College London, who was involved in the research. Specialists at Guy's hospital in London have already used the technique to "cherry pick" healthy embryos for seven women at risk of passing on inherited diseases. Five of the women are pregnant and past the first trimester.
Two of the women had embryos screened for DMD, an x-linked disease which causes crippling muscle wastage. About 100 boys are born with DMD in Britain every year and their average life expectancy is 17 years. Two more women were at risk of passing on cystic fibrosis. While 70% of CF is caused by a well-known genetic mutation that can easily be picked up by screening, the women were among the 30% who carry an unknown mutation that causes the disease. The fifth woman had embryos tested for an unusual condition called hydatidiform mole, in which a fertilised egg grows into a tumour.
The work is due to be revealed at the annual meeting in Prague of the European Society of Human Reproduction and Embryology. The technique, called preimplantation genetic haplotyping, was pioneered by Ali al-Hellani, a Saudi Arabian fertility specialist in 2004, but has been developed further by Pamela Renwick at Guy's hospital genetics centre and Prof Braude, who runs a fertility centre at Kings College, London.
To test for an inherited disease, doctors remove one of eight cells from a three-day-old embryo and extract the tiny amount of DNA from the cell. They then use a technique called multiple displacement amplification to replicate the DNA overnight until there is enough to analyse. Next they take blood samples from family members, including at least one person affected by the disease. By comparing DNA strands of affected and unaffected family members, it is possible to identify the region of a chromosome that is responsible for the disease. The doctors are then able to test embryos to see which have inherited that chromosome and which are disease-free. The treatment costs £4,100.
The Guy's team have applied to the Human Fertilisation and Embryology Authority for licences to test for other genetic diseases, such as fragile X- syndrome which affects one in 4,000 boys and myotonic dystrophy, which affects upwards of one in 8,000.
Stuart Lavery, a fertility expert at Hammersmith hospital, London, said the research would give many couples the first chance of having healthy children. "The idea of a universal tool that can be applied regardless of what the mutation is means many more patients will have access to this," he said.
Case study: Linda Ball, 37, is married to Steven, 38. They live in Daventry, Northamptonshire
Linda Ball was 13 when her brother Vaun died of Duchenne's muscular dystrophy, an inherited muscle-wasting disease that affects boys. He was 18.
Linda was brought up knowing she might be a carrier of the disease and when she and her husband Steven started trying for children she considered having a prenatal test to find out the sex of her baby. The plan was to have an abortion if the test revealed she was carrying a boy.
But when Linda became pregnant, she decided against the test. "I just couldn't bring myself to have an abortion knowing there was a child growing inside me," she said. The couple worked on the basis that by the laws of genetic inheritance, there was a 75% chance the child would be healthy. But Daniel was born five and half years ago and has Duchenne's.
"Unfortunately we were in the 25%. Daniel is a wonderful little boy, he is very intelligent, cheeky and I wouldn't swap him for anyone. But I do blame myself sometimes for passing on this terrible disease," she said. "There is nothing worse than knowing you are going to watch your own child die." Linda became pregnant again some years later, and decided to have the test, even though she knew that again, she would not have an abortion if the baby was male. A scan revealed there was a 95% chance the baby was a girl. After a traumatic pregnancy, Linda gave birth to Helena, who is now one. She has not yet been tested to see if she carries the genetic mutation that causes Duchenne's, but her parents have decided to allow her to decide whether to have the test herself when she is 16.
Linda believes that the PGH test, which could diagnose Duchenne's from one cell taken from a three-day-old IVF embryo before it has been implanted, is easier to consider than a test that could lead to an abortion. "At this point, you're talking about cells, not a foetus that looks like a human being that you're carrying inside yourself. It's never going to be an easy decision, but it is different," she said.
• This article was amended on 15 November 2013. The original version said "Some inherited conditions, known as x-linked diseases, are only passed on to boys". The vast majority of those affected by x-linked diseases are male, but some of those affected are females. As it says in an article on the Wellcome Trust website, "Affected females, with two deficient X chromosomes, are the rare products of a marriage between an affected male and a carrier female."