Gene therapy for "normal" embryos

Genome editing was tested on viable human embryos

Anna Manshina, N+1

Chinese geneticists have edited the genome in viable human embryos for the first time. It turned out that the CRISPR/Cas9 editing system corrects genetic mutations in them more effectively than in "abnormal" embryos that geneticists have worked with before. An article about the study was published by the journal Molecular Genetics and Genomics (Tang et al., CRISPR/Cas9-mediated gene editing in human zygotes using Cas9 protein).

To date, it is possible to avoid hereditary genetic diseases in newborns by diagnosing and selecting healthy embryos for IVF. But this method helps only when there are healthy embryos, and such cases are quite rare. An effective alternative to this method can be editing the embryo genome using the CRISPR/Cas9 method. This method is already being used in the first clinical trials to correct genetic errors in somatic cells (i.e. those that are not involved in the production of sex cells). However, editing the genome at the level of the whole embryo implies the inevitable transmission of changes by inheritance, which raises concerns of some scientists and politicians. There is no consensus on the legal status of such studies in Western countries yet, but in China there are no ethical restrictions on working with the embryo and the human sexual line now. Two years ago, a group of Chinese geneticists published the first results of editing the embryonic genome. Scientists used only non-viable embryos that could not develop into a fetus. Then the efficiency of CRISPR/Cas9 was very low, it was possible to correct mutations in only one embryo out of ten.

In a new study, geneticists tested CRISPR/Cas9 on "normal" embryos that can develop into a fetus. The researchers used immature eggs rejected for IVF. They brought these eggs to maturity and fertilized them with sperm from two men with different genetic diseases.

The first donor had a G1376T mutation in the G6PD enzyme gene. This mutation is a common cause of favism, a disease in which the consumption of certain foods, such as beans, causes damage to red blood cells and anemia. In one of the two embryos from this donor, CRISPR/Cas9 completely corrected the mutation. In the second case, the system corrected the mutation only in part of the cells, and in the remaining cells the G6PD gene was simply turned off, the embryo became "mosaic".

The second donor had a mutation beta41-42, which causes beta-thalassemia, a blood disease associated with impaired hemoglobin synthesis. Using the sperm of this donor, the scientists obtained four embryos. But the editing system worked correctly only in one of them, eliminating the mutation in part of the cells. In two more cases, CRISPR/Cas9 did not work at all, and in one it introduced an additional mutation. As a result, the CRISPR/Cas9 genome editing system successfully corrected mutations in half of the embryos, in one completely and in two partially. All the embryos were subsequently destroyed, it was not planned to plant them to continue pregnancy.

Despite the fact that the study is very small and the efficiency of genome editing is still low, its results are already much better than those of previous similar experiments with non-viable embryos.

Portal "Eternal youth" http://vechnayamolodost.ru  10.03.2017