13 April 2015
ByAppeared in BioNews 797
The screening technique, called karyomapping, is a type of PGD (preimplantation genetic diagnosis) procedure. Current PGD methods are developed on a case-by-case basis to test embryos for the presence of a specific mutation found in one or both of the parents' DNA and can involve months of laboratory work.
Karyomapping, on the other hand, can test for the same diseases, but can be completed much faster and is no more expensive than traditional PGD methods. It can also be used to check that embryos have the correct number of chromosomes.
Mrs Carmen Meagu suffers from Charcot-Marie-Tooth disease, a group of rare disorders of the peripheral nervous system that cause muscle degeneration and sensation loss in the feet and hands. She inherited the disease from her father, and had a 50 percent chance of passing it on to her children.
Speaking to The Telegraph, Mrs Meagu said: 'For me the risk was too high. I was told I could try and get pregnant and have a test at 16 weeks, but that really wasn't an option for me because it would have been too hard to have an abortion at that stage.
'Then we were told about a clinic in London which could screen the disease out, and we felt we had to try'.
The technique involves using DNA from Mrs Meagu, her husband Gabriel, and another family member, to compare roughly 300,000 different points across the genome called SNPs (single nucleotide polymorphisms). This allows scientists to find characteristic features that are unique to the chromosome carrying the defective gene. Following a standard IVF cycle, embryos are biopsied to find out which ones are free of the genetic disease.
Mr Paul Serhal is the founder and medical director of the Centre for Reproductive and Genetic Health, where the technique was used in December 2013. Also speaking to The Telegraph, he explained: 'Essentially, karyomapping finds a fingerprint that is unique to the chromosome that carries the defective gene.
'It is then possible to test embryos produced using IVF for this presence of this fingerprint. Whenever the fingerprint is seen in an embryo it means that it has inherited the chromosome carrying the defective gene. The test checked for Charcot Marie Tooth disease and at the same time for chromosomal abnormalities, such as Down's syndrome, enabling us to avoid inadvertently transferring an embryo which may otherwise not have been viable.'
Mr and Mrs Meagu's son Lucas was born in December 2014. Mrs Meagu said: 'I obviously worry, like all mothers, but now I worry about normal things. I know for sure that he is not only free of Charcot-Marie-Tooth disease but also other illnesses. I would recommend it to any other mother who is worried about passing on an illness.'
Karyomapping was developed by a team led by Professor Darren Griffin at the University of Kent, in collaboration with researchers at Illumina. It is now available on the NHS for genetic diseases that are licensed by the Human Fertilisation and Embryology Authority.