New Universal Embryo Test Can Detect 15,000 Genetic Diseases



The Times (London) reports on the development of a new pre-implantation genetic test called karyomapping:

Karyomapping … can be performed within a few weeks, for any inherited condition. At present, costs are comparable to the £1,500 price tag of standard PGD (pre-implantation genetic diagnosis), but these are expected to fall significantly as the technology is developed.

DNA samples are first obtained from the parents and a close relative, usually a child who has the disease in question. This can be done using a noninvasive cheek swab.

This information is then compared with DNA from an embryo, obtained by a biopsy in similar fashion to PGD, to map how its chromosomes are built from the genetic material of its four grandparents. The map can determine whether the embryo has inherited chunks of chromosome that contain any faulty gene…

Karyomapping works by analysing chromosomes – the packets that hold genes. Humans have 46 chromosomes arranged into two sets of 23, one provided by the mother and one by the father, through eggs and sperm.

When these are made, they each receive just one set of 23 chromosomes, so that when they fuse they create an embryo with the normal complement of 46.

During this process, a man's sperm acquires some blocks of DNA that originally came from his mother (the embryo's grandfather), and some that he inherited from his father (the embryo's grandfather). The same applies to a woman's eggs.

Karyomapping involves drawing up a chart of where these grandparental chunks lie on an embryo's chromosomes. This can be done by comparing DNA from the parents, at least one close relative, and the embryo itself.

Scientists examine more than 300,000 DNA markers throughout the genetic code, which together can show which grandparent provided a particular block of DNA. Once the map is complete, it can be examined for faulty genes.

It is not necessary to know the DNA code of a particular mutation, only its position on a chromosome and the grandparent who passed it on. The gene that causes cystic fibrosis, for example, lies on chromosome 7. If the embryo's paternal grandfather was a carrier, and the embryo has inherited a chunk of his DNA at the critical position, it will have the faulty gene.

The same thing can be done again and again across all the chromosomes, to allow screening for multiple genes. In practice, this is difficult for more than two or three traits, because few embryos will have the desired DNA at every point. A karyomap could also be reused after a screened embryo has developed into a child. This could reveal genes that give a raised risk of Alzheimer's or heart disease.

As the Times headline suggests, widespread use of karyomapping "could kill off inherited illnesses." 

Whole Times story here