Resistance to a CRISPR-based gene drive at an evolutionarily conserved site is revealed by mimicking genotype fixation

CRISPR-based homing gene drives can be designed to disrupt essential genes whilst biasing their own inheritance, leading to suppression of mosquito populations in the laboratory. This class of gene drives relies on CRISPR-Cas9 cleavage of a target sequence and copying ('homing') therein of the gene drive element from the homologous chromosome. However, target site mutations that are resistant to cleavage yet maintain the function of the essential gene are expected to be strongly selected for. Targeting functionally constrained regions where mutations are not easily tolerated should lower the probability of resistance. Evolutionary conservation at the sequence level is often a reliable indicator of functional constraint, though the actual level of underlying constraint between one conserved sequence and another can vary widely. Here we generated a novel adult lethal gene drive (ALGD) in the malaria vector Anopheles gambiae, targeting an ultra-conserved target site in a haplosufficient essential gene (AGAP029113) required during mosquito development, which fulfils many of the criteria for the target of a population suppression gene drive. We then designed a selection regime to experimentally assess the likelihood of generation and subsequent selection of gene drive resistant mutations at its target site. We simulated, in a caged population, a scenario where the gene drive was approaching fixation, where selection for resistance is expected to be strongest. Continuous sampling of the target locus revealed that a single, restorative, in-frame nucleotide substitution was selected. Our findings show that ultra-conservation alone need not be predictive of a site that is refractory to target site resistance. Our strategy to evaluate resistance in vivo could help to validate candidate gene drive targets for their resilience to resistance and help to improve predictions of the invasion dynamics of gene drives in field populations.

Systemic Capillary Leak Syndrome triggered by SARS-CoV2 infection: Case Report and Systematic Review

Objective: Systemic capillary leak syndrome (SCLS) is a severe condition characterized by the coexistence of hypovolaemic shock, haemococentration, and hypoalbuminaemia, without albuminuria, that may progress to multiorgan failure and an unfavourable outcome. Its development is often triggered by viral infections, such as influenza A virus, but it is unclear whether it is also triggered by severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2). We aimed to investigated the association between SARS-CoV-2 and SCLS.Method: We present the case of a 55-year-old-woman affected by SARS-CoV-2 infection who developed SCLS. Moreover, we performed a systematic review of the literature to identify any common features with other cases and to describe clinical characteristics and outcomes.Results: We found three other cases of SCLS occurring during SARS-CoV-2 infection in 2020. Taking all cases together, the mean age was 50 years (range 38-63), with a 1:1 gender ratio. Respiratory manifestations were the most common symptom, and all patients required admission to the intensive care unit. The mortality rate was 50%.Conclusions: SARS-CoV-2 infection may trigger SCLS disease, either by an overproduction of proinflammatory cytokines or by direct viral infection of the endothelium. Since SCLS may have a poor prognosis, in every SARS-CoV-2-infected patient presenting the suggestive triad of hypovolaemic shock, haemoconcentration, and hypoproteinaemia, an SCLS diagnosis should be considered and early treatment initiated.