Changes in a new type of genomic accordion may open the pallets to increased monkeypox transmissibility

The currently expanding monkeypox epidemic is caused by a subclade IIb descendant of a monkeypox virus (MPXV) lineage traced back to Nigeria in 1971. In contrast to monkeypox cases caused by clade I and subclade IIa MPXV, the prognosis of current cases is generally favorable, but person-to-person transmission is much more efficient. MPXV evolution is driven by selective pressure from hosts and loss of virus–host interacting genes. However, there is no satisfactory genetic explanation using single-nucleotide polymorphisms (SNPs) for the observed increased MPXV transmissibility. We hypothesized that key genomic changes may occur in the genome’s low-complexity regions (LCRs), which are highly challenging to sequence and have been dismissed as uninformative. Using a combination of highly sensitive techniques, we determined a first high-quality MPXV genome sequence of a representative of the current epidemic with LCRs resolved at unprecedented accuracy. This effort revealed significant variation in short-tandem repeats within LCRs. We demonstrate that LCR entropy in the MPXV genome is significantly higher than that of SNPs and that LCRs are not randomly distributed. In silico analyses indicate that expression, translation, stability, or function of MPXV orthologous poxvirus genes (OPGs) 153, 204, and 208 could be affected in a manner consistent with the established “genomic accordion” evolutionary strategies of orthopoxviruses. Consequently, we posit that genomic studies focusing on phenotypic MPXV clade-/subclade-/lineage-/strain differences should change their focus to the study of LCR variability instead of SNP variability. ### Competing Interest Statement The work for this study at Instituto de Salud Carlos III was partially funded by Accion Estrategica Impacto clinico y microbiologico del brote por el virus de la viruela del mono en pacientes en Espana (2022): proyecto multicentrico MONKPOX-ESP22 (CIBERINFEC). The work for this study at the GP laboratory was funded by instiutional funds of the Department of Microbiology, Icahn School of Medicine at Mount Sinai in support of Global Health Emerging Pathogen Institute activities. The A.G.-S. laboratory has received research support from Pfizer, Senhwa Biosciences, Kenall Manufacturing, Blade Therapuetics, Avimex, Johnson & Johnson, Dynavax, 7Hills Pharma, Pharmamar, ImmunityBio, Accurius, Nanocomposix, Hexamer, N-fold LLC, Model Medicines, Atea Pharma, Applied Biological Laboratories and Merck, outside of the reported work. A.G.-S. has consulting agreements for the following companies involving cash and/or stock: Castlevax, Amovir, Vivaldi Biosciences, Contrafect, 7Hills Pharma, Avimex, Vaxalto, Pagoda, Accurius, Esperovax, Farmak, Applied Biological Laboratories, Pharmamar, Paratus, CureLab Oncology, CureLab Veterinary, Synairgen and Pfizer, outside of the reported work. A.G.-S. has been an invited speaker in meeting events organized by Seqirus, Janssen, Abbott and Astrazeneca. A.G.-S. is inventor on patents and patent applications on the use of antivirals and vaccines for the treatment and prevention of virus infections and cancer, owned by the Icahn School of Medicine at Mount Sinai, New York, outside of the reported work.