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One-Stop Genetic Test For Embryos Unveiled

6 July 2009
Appeared in BioNews 515

A one-step gene mapping test for identifying genetic and chromosomal abnormalities in embryos may be available in the UK within a year. The technique, known as karyomapping, can screen for almost any inherited disease and is much faster than those currently available as it does not need prior knowledge of the specific gene mutation involved. The method was unveiled last week at the annual conference of the European Society for Human Reproduction and Embryology (ESHRE), in Amsterdam, after researchers from the UK and US announced they had successfully screened cells taken from donated embryos that were known to have cystic fibrosis (CF).

Since 1989, couples who are known to be at risk of having a child with a genetic disorder have had the option of screening their embryos using a technique called PGD (preimplantation genetic diagnosis). PGD involves identifying the exact mutation causing a particular disease in a particular family, then spending many months developing a custom test. The process costs several thousand pounds and can only pick up two per cent of known genetic disorders.

Now, for a similar price, karyomapping can identify any known genetic disorder and is faster because scientists do not need to know the exact DNA mutation they are looking for. Instead they compare the DNA of affected and unaffected family members to work out which DNA section is carried only by those affected by the condition. Embryos can then be screened for this section of DNA to find out if they have inherited the mutation. In practice this involves DNA comparisons at over 300,000 locations genome-wide, but can be achieved rapidly through current microchip technology known as 'microarrays'. Another advantage is that karyomapping can simultaneously check for abnormal numbers of any of the 23 pairs of chromosomes, which can lead to conditions such as Down syndrome or trigger miscarriages.

'The hope is that clinicians will be able to test embryos for specific genetic diseases and know that, with one test, they are transferring chromosomally normal embryos. This will be a step forward from current technology that is mostly limited to choosing one test or the other,' explained karyomapping's inventor, Professor Alan Handyside of the London Bridge Fertility Gynaecology and Genetics Centre in London.

Some have argued the new technique may add to the controversy over 'designer babies' because it widens the range of genetic characteristics for which embryos can be screened and could theoretically be used to screen for non-serious conditions, or non-medical traits such as blue eyes. Professor Handyside believes this is not an issue because the relevant regulations in the UK are very strict and would remain so. 'We're not mad Frankensteins working away in our laboratories to create designer babies. We are only allowed to look for major diseases which cause handicaps,' he retorted.

Elsewhere at ESHRE scientists announced that up to 90 per cent of IVF embryos contain chromosomal abnormalities, even those produced by young, fertile couples. The surprising finding implies that current PGD techniques do nothing to improve pregnancy and live birth rates, and can potentially lead to viable embryos being discarded. This news means that the timely announcement of the new karyomapping method will be warmly welcomed by many.

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