Human telomere biology disorders (TBD) and short telomere syndromes (STS) are a group of illnesses caused by hereditary loss-of-function mutations in telomere-related genes. For the study, researchers discovered three germline heterozygous missense variations in the RPA1 gene in 4 unrelated probands with short telomeres and various clinical characteristics of TBD/STS, such as bone marrow failure, myelodysplastic syndrome, T- and B-cell lymphopenia, pulmonary fibrosis, or cutaneous symptoms. 

All variations were associated with the RPA1 protein’s DNA-binding domain A. RPA1 is a single-strand DNA-binding protein that is needed for DNA replication and repair, as well as telomere preservation. RPA1E240K and RPA1V227A proteins have higher binding to single-strand and telomeric DNA, reflecting a gain in DNA-binding activity, but RPA1T270A exhibits binding characteristics equal to the wild-type protein. CRISPR/Cas9 was utilized to insert the RPA1E240K mutation into healthy inducible pluripotent stem cells in order to investigate the mutational impact in a biological system. 

As a result, telomeres were severely shortened, and hematopoietic differentiation was compromised. In addition, in patients with RPA1E240K, researchers identified somatic genetic rescue in hematopoietic cells due to an acquired truncating cis RPA1 mutation or a uniparental isodisomy 17p with loss of mutant allele, which coincided with stable blood levels. The 2 somatic genetic rescue events were demonstrated to be acquired separately in hematopoietic stem cells using single-cell sequencing. In summary, they provide the first case of TBD/STS caused by germline RPA1 mutations.