AD	Anxiety Disorders
ADD	Attention Deficit Disorder
ADHD	Attention Deficit and Hyperactivity Disorder
BD	Bipolar Disorder
CNS	Central Nervous System
CARS	Childhood Autism Rating Scale
CD	Coeliac Disease
CRP	C-Reactive Protein
DAO	Diamine Oxidase
GI	Gastro-Intestinal
GALT	Gut-Associated Lymphoid Tissue
GBA	Gut-Brain Axis
HPA	Hypothalamic Pituitary Adrenal Axis
IL-6	Interleukin 6
IP	Intestinal Permeability
LPS	Lipopolysaccharide
LBP	Lipopolysaccharide Binding Protein
MDD	Major Depressive Disorder
NOS	Newcastle-Ottawa Scale
NCGS	Non-Coeliac Gluten Sensitivity
OCD	Obsessive–Compulsive Disorder
PANS	Pediatric Acute-onset Neuropsychiatric Syndrome
PANDAS	Pediatric Autoimmune Neuropsychiatric Disorders Associated with Streptococcal Infections
PRISMA	Preferred Reporting Items for Systematic Reviews and Meta-Analysis
PICO	Participants, Interventions, Comparisons, Outcomes
SCZ	Schizophrenia
sIgA	Secretory IgA
STROBE	Strengthening the Reporting of Observational Studies in Epidemiology
TG6	Transglutaminase 6
TG2	Type 2 Tissue Transglutaminase
ZTM	Zonulin Transgenic Mouse Model