ABC	Aberrant Behavior Checklist;
ABC-2	Aberrant Behavior Checklist second edition;
AFU	Active Fluorescent Units;
ASD	autism spectrum disorders;
ATECAutism	Treatment Evaluation Checklist;
CARS	Childhood Autism Rating Scale;
CFU	colony-forming units;
CNS	central nervous system;
CGI	Clinical Global Impression;
CPRS-R	Conners’ Parent Rating Scale—Revised;
FDA	Food and Drug Administration;
FMT	fecal microbiota transplantation;
GABA	gamma-aminobutyric acid;
GI	gastrointestinal;
GM	gut microbiota;
GOS	galactooligosaccharides;
GR	glucoraphanin;
ISAPP	International Scientific Association for Probiotics and Prebiotics;
IU	international unit;
KD	ketogenic diet;
LPS	lipopolysaccharide;
MGBA	microbiota–gut–brain axis;
MTT	microbiota transfer therapy;
OXT	oxytocin;
PEG	polyethylene glycol;
PICOS	population, intervention, comparison, outcome, study design;
PRISMA	Preferred Reporting Items for Systematic Reviews and Meta-Analyses;
PRIMSA-Scr	PRISMA Extension for Scoping Reviews;
PROSPERO	International Prospective Register of Systematic Reviews;
RBS-R	Repetitive Behavior Scale—Revised;
SCFA	short-chain fatty acids;
SHGM	Standardized Human Gut Microbiota;
SpCO	carboxyhemoglobin;
SRS	Social Responsiveness Scale;
TD	typically developing.