The distinct features of microbial 'dysbiosis' of Crohn's disease do not occur to the same extent in their unaffected, genetically-linked kindred.

BACKGROUND/AIMS: Studying the gut microbiota in unaffected relatives of people with Crohn's disease (CD) may advance our understanding of the role of bacteria in disease aetiology. METHODS: Faecal microbiota composition (16S rRNA gene sequencing), genetic functional capacity (shotgun metagenomics) and faecal short chain fatty acids (SCFA) were compared in unaffected adult relatives of CD children (CDR, n = 17) and adult healthy controls, unrelated to CD patients (HUC, n = 14). The microbiota characteristics of 19 CD children were used as a benchmark of CD 'dysbiosis'. RESULTS: The CDR microbiota was less diverse (p = 0.044) than that of the HUC group. Local contribution of ß-diversity analysis showed no difference in community structure between the CDR and HUC groups. Twenty one of 1,243 (1.8%) operational taxonomic units discriminated CDR from HUC. The metagenomic functional capacity (p = 0.207) and SCFA concentration or pattern were similar between CDR and HUC (p>0.05 for all SCFA). None of the KEGG metabolic pathways were different between these two groups. Both of these groups (HUC and CDR) had a higher microbiota α-diversity (CDR, p = 0.026 and HUC, p<0.001) with a community structure (ß-diversity) distinct from that of children with CD. CONCLUSIONS: While some alterations were observed, a distinct microbial 'dysbiosis', characteristic of CD patients, was not observed in their unaffected, genetically linked kindred.