Sunday, November 24, 2019

Deafness Gene GJB2 Edited in Human Eggs

Denis Rebrikov is a Russian biologist that started editing the GJB2 gene, associated with deafness, in human eggs donated by women who can hear. The GJB2 gene produces a protein in gap junctions, the channels that help move chemical signals like potassium between cells, including in the inner ear. Rebrikov told Science that he plans to do extensive safety checks before seeking approval to implant an edited embryo. First, he wants to sequence the entire genomes of each parent to get a baseline for assessing off-target mutations in their edited embryos. He then wants to stimulate the woman’s ovaries, obtain about 20 eggs, fertilize them with her partner’s sperm, and finally add the mutation fixing CRISPR. He’ll grow these embryos for 5 days, at which point they will have about 250 cells and be in the blastocyst stage. Then he will do repeated rounds of whole-genome sequencing of 10 of these blastocysts, which will reveal all mutations that differ from the genomes of the parents. he will move to the next stage with the remaining edited embryos: a preimplantation test, then he will check the cells for many types of genetic defects and for mosaicism for the CRISPR edit.

He does not plan to create gene-edited babies just yet. He is studying normal copies of GJB2 to better understand potentially harmful mutations associated with using CRISPR. His eventual goal is to edit the eggs of deaf women in order to allow deaf couples with GJB2 mutations to have children with functioning copies of the gene and typical hearing. The experiment is similar to work done by researcher He Jiankui, who announced last year that he had created CRISPR-edited twin babies whose genomes were modified in hopes of making them resistant to HIV.


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