Molecular Characterisation of Gastrointestinal Microbiota of Children With Autism (With and Without Gastrointestinal Dysfunction) and Their Neurotypical Siblings

Two studies showed increases in alpha diversity and six studies showed no significant changes in alpha diversity.

“Two studies showed increases [31, 33] and six studies showed no significant changes in alpha diversity [36, 42, 43, 48, 50, 54].”

Among seven papers reporting beta diversity, four showed significant differences in beta diversity between ASD and SIB/HC while the rest did not.

“Among the seven [31, 36, 40–42, 48, 50] papers that reported on beta diversity, four [31, 40, 41, 50] papers showed significant differences in beta diversity between ASD and SIB/HC while the rest did not (Additional file 1: Table S2).”

The rest of the studies observed either a decrease in Bacteroidetes percentage or no significant differences between cases and controls.

“The rest of the studies observed either a decrease in Bacteroidetes percentage [50, 54] or no significant differences between cases and controls [31, 36, 48].”

At the Firmicutes phylum level, none of the six studies showed an increase in absolute or relative abundance.

“At the phylum level, none of the six studies showed an increase in absolute or relative abundance [31, 33, 36, 48, 51, 54].”

For relative abundance in total and metabolically active Firmicutes, studies demonstrated either a decrease or no significant differences between children with ASD, SIB, and HC.

“For relative abundance in both total and metabolically active Firmicutes, the studies demonstrated either a decrease [31, 33, 36] or no significant differences between children with ASD, SIB, and HC [48, 51, 54].”

Actinobacteria as a phylum did not reveal any compelling results.

“Actinobacteria as a phylum did not reveal any compelling results [33, 36, 48];”

No specific findings were identified in the Verrucomicrobia phylum and in the Verrucomicrobiaceae family.

“No specific findings were identified in the Verrucomicrobia phylum [31, 33, 36, 39, 48] and in the Verrucomicrobiaceae family [31, 37, 39, 41, 52].”

Differences in the types and composition of various bacterial species in children with ASD have been reported.

“Differences in the types and composition of various bacterial species in children with ASD have been reported.22, 23, 24, 25, 26, 27”

More recent studies failed to reach a consensus as to whether an ASD-specific microbial signature exists.

“but more recent studies failed to reach a consensus as to whether an ASD-specific microbial signature exists.24, 51”

In our meta-analysis, only two studies enrolled children with ASD who had no GI symptoms, and one study did not provide details about GI symptoms.

“In our meta-analysis, only two studies enrolled children with ASD who had no GI symptoms (23, 37), and one study did not provide details about GI symptoms (33).”

Son et al., De Angelis et al. and Gondalia et al. recruited healthy siblings as control, whereas other studies recruited normal control from the whole population.

“Besides, Son et al.21, De Angelis et al.23 and Gondalia et al.26 recruited healthy siblings as control, whereas other studies recruited normal control from the whole population.”

It can be an alternative explanation that studies using NT sibling controls did not find any significant difference, while other studies using non-sibling controls did.

“It can be an alternative explanation that why studies21,26 using NT sibling controls did not find any significant difference, while other studies using non-sibling controls did.”