Diagnosis and treatment of autism spectrum disorder

A method for improving behavioral performance in a subject suffering from anxiety, Fragile X, Rett syndrome, obsessive compulsive disorder, attention deficit disorder, autistic disorder (classic autism), Asperger's disorder (Asperger syndrome), pervasive developmental disorder not otherwise specified (PDD-NOS), childhood disintegrative disorder (CDD), or autism spectrum disorder (ASD), the method comprising:

• (a) measuring the blood level of 4-ethylphenylsulfate in the subject,
• wherein the blood level of said 4-ethylphenylsulfate in the subject is altered relative to the blood level of said 4-ethylphenylsulfate observed in a subject not suffering from or showing symptoms of anxiety, Fragile X, Rett syndrome, obsessive compulsive disorder, attention deficit disorder, autistic disorder (classic autism), Asperger's disorder (Asperger syndrome), pervasive developmental disorder not otherwise specified (PDD-NOS), childhood disintegrative disorder (CDD), or ASD;
• and
• (b) administering a composition comprising bacteria selected from the group consisting of B. fragilis, B. thetaiotaomicron, and B. vulgatus to the subject until a correction of the deficiency in at least one of the one or more symptoms of anxiety, Fragile X, Rett syndrome, obsessive compulsive disorder, attention deficit disorder, autistic disorder (classic autism), Asperger's disorder (Asperger syndrome), pervasive developmental disorder not otherwise specified (PDD-NOS), childhood disintegrative disorder (CDD), or ASD is observed.