Base editing is a new method of gene editing.

The traditional CRISPR-Cas9 editing technique depends on making a targeted (using a guide RNA) double-strand DNA break (DSB). This DSB is repaired by the error-prone non-homologous end joining, causing disruption of the gene, or homology-directed repair using a template DNA. Correction of faulty genes by this technique proved to be difficult and of low efficiency. See applications described in this site here and here.

DNA base editing also uses a guide RNA to find the target sequence, then makes a transition mutation in DNA. Cytosine base editing (CBE) uses a cytosine deaminase to convert cytosine to uracil, which is recognized as thymine during DNA replication. Thus, the C-G base pair becomes T-A. Adenosine base editing (ABE) uses an adenosine deaminase to convert adenosine to inosine, which is recognized as guanosine. Thus, the A-T base pair becomes G-C by replication.

Base editing has a potential application in treating diseases caused by single nucleotide mutation. The continuous developing of new techniques carries the hope of treating such diseases with a high efficiency.

You can find a 2020 review of this subject here

Please refer to this post for the clinical application that has just started:

https://bioinformaticshub.net/news/clinical-application-of-base-editing-started/