A CRISPR base editing approach for the functional assessment of telomere biology disorder-related genes in human health and aging.

Telomere Biology Disorders (TBDs) are a group of rare diseases characterized by the presence of short and/or dysfunctional telomeres. They comprise a group of bone marrow failure syndromes, idiopathic pulmonary fibrosis, and liver disease, among other diseases. Genetic alterations (variants) in the genes responsible for telomere homeostasis have been linked to TBDs. Despite the number of variants already identified as pathogenic, an even more significant number must be better understood. The study of TBDs is challenging since identifying these variants is difficult due to their rareness, it is hard to predict their impact on the disease onset, and there are not enough samples to study. Most of our knowledge about pathogenic variants comes from assessing telomerase activity from patients and their relatives affected by a TBD. However, we still lack a cell-based model to identify new variants and to study the long-term impact of such variants on the genes involved in TBDs. Herein, we present a cell-based model using CRISPR base editing to mutagenize the endogenous alleles of 21 genes involved in telomere biology. We identified key residues in the genes encoding 17 different proteins impacting cell growth. We provide functional evidence for variants of uncertain significance in patients with TBDs. We also identified variants resistant to telomerase inhibition that, similar to cells expressing wild-type telomerase, exhibited increased tumorigenic potential using an in vitro tumour growth assay. We believe that such cell-based approaches will significantly advance our understanding of the biology of TBDs and may contribute to the development of new therapies for this group of diseases.