Microdiversity of Enterococcus faecalis isolates in cases of infective endocarditis: selection of non-synonymous mutations and large deletions is associated with phenotypic modifications.

Context: Today, infective endocarditis (IE) caused by Enterococcus faecalis represents 10% of all IE and is marked by its difficult management and the frequency of relapses. Although the precise reasons for that remain to be elucidated, the evolution of the culprit strain under selective pressure through microdiversification could be, at least in part, involved. Material and methods: To further study the in situ genetic microdiversity and its possible phenotypic manifestations in E. faecalis IE, we sequenced and compared multiple isolates from the valves, blood culture and joint fluid of five patients who underwent valvular surgery. Growth rate and early biofilm production of selected isolates were also compared. Results: By sequencing a total of 58 E. faecalis genomes, we detected a considerable genomic microdiversity, not only among strains from different anatomical origins, but also between isolates from the same studied cardiac valves. Interestingly, deletions of thousands of bases including the well-known virulence factors ebpA/B/C, and srtC, as well as other large prophage sequences containing genes coding for proteins implicated in platelet binding (PlbA and PlbB) were evidenced. The study of mutations helped unveil common patterns in genes related to the cell cycle as well as central metabolism, suggesting an evolutionary convergence in these isolates. As expected, such modifications were associated with a significant impact on the in-vitro phenotypic heterogeneity, growth, and early biofilm production. Conclusion: Genome modifications associated with phenotypic variations may allow bacterial adaptation to both antibiotic and immune selective pressures, and thus promote relapses.

Towards a better understanding of adult idiopathic epidermal necrolysis: a retrospective study of 19 cases.

BACKGROUND: Most cases of Stevens-Johnson syndrome and toxic epidermal necrolysis are drug-induced. A small subset of cases remain with unknown aetiology (idiopathic epidermal necrolysis [IEN]). OBJECTIVE: We sought to better describe adult IEN and understand the aetiology. METHODS: This retrospective study was conducted in 4 centres of the French national reference centre for epidermal necrolysis. Clinical data were collected for the 19 adults hospitalized for IEN between January 2015 and December 2019. Wide toxicology analysis of blood samples was performed. Histology of IEN cases was compared with blinding to skin biopsies of drug-induced EN (DIEN, 'controls'). Available baseline skin biopsies were analysed by shotgun metagenomics and transcriptomics and compared to controls. RESULTS: IEN cases represented 15.6% of all EN cases in these centres. The median age of patients was 38 (range 16-51) years; 68.4% were women. Overall, 63.2% (n = 12) of cases required intensive care unit admission and 15.8% (n = 3) died at the acute phase. Histology showed the same patterns of early- to late-stage EN with no difference between DIEN and IEN cases. One toxicology analysis showed unexpected traces of carbamazepine; results for other cases were negative. Metagenomics analysis revealed no unexpected pathological microorganism. Transcriptomic analysis highlighted a different pro-apoptotic pathway in IEN compared to DIEN, with an overexpression of apoptosis effectors TWEAK/TRAIL. CONCLUSIONS: IEN affects young people and is a severe form of EN. A large toxicologic investigation is warranted. Different pathways seem involved in IEN and DIEN, leading to the same apoptotic effect, but the primary trigger remains unknown.

ARL2BP mutations account for 0.1% of autosomal recessive rod-cone dystrophies with the report of a novel splice variant.

We report a novel ARL2BP splice site mutation after whole-exome sequencing (WES) applied to a Moroccan family including two sisters affected with autosomal recessive rod-cone dystrophy (arRCD). Subsequent analysis of 844 index cases did not reveal further pathogenic chances in ARL2BP indicating that mutations in ARL2B are a rare cause of arRCD (about 0.1%) in a large cohort of French patients.

Next-generation sequencing confirms the implication of SLC24A1 in autosomal-recessive congenital stationary night blindness.

Congenital stationary night blindness (CSNB) is a clinically and genetically heterogeneous retinal disorder which represents rod photoreceptor dysfunction or signal transmission defect from photoreceptors to adjacent bipolar cells. Patients displaying photoreceptor dysfunction show a Riggs-electroretinogram (ERG) while patients with a signal transmission defect show a Schubert-Bornschein ERG. The latter group is subdivided into complete or incomplete (ic) CSNB. Only few CSNB cases with Riggs-ERG and only one family with a disease-causing variant in SLC24A1 have been reported. Whole-exome sequencing (WES) in a previously diagnosed icCSNB patient identified a homozygous nonsense variant in SLC24A1. Indeed, re-investigation of the clinical data corrected the diagnosis to Riggs-form of CSNB. Targeted next-generation sequencing (NGS) identified compound heterozygous deletions and a homozygous missense variant in SLC24A1 in two other patients, respectively. ERG abnormalities varied in these three cases but all patients had normal visual acuity, no myopia or nystagmus, unlike in Schubert-Bornschein-type of CSNB. This confirms that SLC24A1 defects lead to CSNB and outlines phenotype/genotype correlations in CSNB subtypes. In case of unclear clinical characteristics, NGS techniques are helpful to clarify the diagnosis.