Quick questions on Future directions of genetic research: germline editing, gene drives and synthetic biology: HSC Biology Module 6

The deepest impact of editing the germline is that the change is heritable. A somatic edit treats one patient and stops there; a germline edit is built into the embryo, so it is copied into every cell, including that person's eggs or sperm, and is therefore passed to their children, their grandchildren, and so on. This is exactly why germline editing is treated so differently from ordinary gene therapy.

Technically possible since 2014 (CRISPR in mouse embryos) and demonstrated in humans by He Jiankui in 2018, who edited the CCR5 gene in twin embryos in an attempt to confer HIV resistance. He was prosecuted in China and the scientific community condemned the experiment as premature and unethical.

Prevention of severe inherited disease in families where preimplantation diagnosis cannot help (both parents homozygous for a recessive condition).

Banned or strictly limited in almost every jurisdiction; a global moratorium has been proposed by leading scientists.

Irreversibility, cross-border spread, ecosystem consequences, governance gap.

A "search and replace" CRISPR system that can write small new sequences into a chosen location without a double-strand break. Lower off-target rate than original CRISPR-Cas9. Approaching clinical trials for sickle cell and other monogenic diseases.

Converts one base directly to another (e.g. C to T) without cutting both strands. Verve Therapeutics has run trials for inherited hypercholesterolaemia.

"Evaluate" wants a justified judgement weighing benefits against impacts; "compare" wants the same features for both technologies (e.g. somatic vs germline); "explain" wants the mechanism, not just the outcome.

Somatic = body cells, not inherited; germline (and gene drives) = inherited. This single distinction underpins most marks on the impacts of these technologies.