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Background: Most schwannomas are isolated tumours occurring in otherwise healthy people. However, bilateral vestibular schwannomas (BVS) or multiple non-vestibular schwannomas indicate an underlying genetic predisposition. This is most commonly NF2 -related schwannomatosis (SWN), but when BVS are absent, this can also indicate SMARCB1 -related or LZTR1 -related SWN., Methods: We assessed the variant detection rates for the three major SWN genes ( NF2 , LZTR1 and SMARCB1 ) in 154 people, from 150 families, who had at least one non-vestibular schwannoma, but who did not meet clinical criteria for NF2 -related SWN at the time of genetic testing., Results: We found that 17 (11%) people from 13 families had a germline SMARCB1 variant and 19 (12%) unrelated individuals had a germline LZTR1 variant. 19 people had an NF2 variant, but 18 of these were mosaic and 17 were only detected when 2 tumours were available for testing. The overall detection rate was 25% using blood alone, but increased to 36% when tumour analysis was included. Another 12 people had a germline variant of uncertain significance (VUS)., Conclusions: There were similar proportions of LZTR1 , SMARCB1 or mosaic NF2 . However, since an NF2 variant was detected in tumours from 103 people, it is likely that further cases of mosaicism would be detected if more people had additional tumours available for analysis. In addition, if further evidence becomes available to show that the VUSs are pathogenic, this would significantly increase the proportion of people with a genetic diagnosis. Our results indicate the importance of comprehensive genetic testing and improved variant classification., Competing Interests: Competing interests: GE has received consultancy fees from AstraZeneca, Springworks and Everything Genetic., (© Author(s) (or their employer(s)) 2024. No commercial re-use. See rights and permissions. Published by BMJ.)

Some antibiotics tend to select for R-factor-carrying Escherichia coli in the human gut, with complex long-term consequences. Some resistant strains disappear rapidly when treatment ends, while others persist for months in the absence of obvious antibiotic selection pressure, and the performance of individual resistant strains seems to depend more on the nature of the strain than on the plasmid carried. R plasmids are relatively rare in those E coli that colonize well in the gut and resistant bacteria therefore tend to disappear when treatment ends, but this situation could change dramatically if R plasmids became prevalent among those strains of E coli that colonize effectively.