Investigators from Brazil determined if copy number variants (CNVs) in glutamate metabotropic receptor genes (GRM) were overrepresented in 1038 individuals with ADHD compared to 1057 subjects without ADHD. No significant difference in the total number of CNVs was found in the two population samples (P = 0.326). The presence of CNVs was associated with lower IQ scores in ADHD samples (P = 0.026) but not in the sample without ADHD. CNVs in GRM5 were associated with anxiety disorders in ADHD cases (P = 0.002), but not in subjects without ADHD. CNVs in the glutamatergic genes were associated with cognitive and clinical characteristics of ADHD. 
COMMENTARY. The results of this study suggest a role for glutamate in ADHD. In an investigation of the association between metabotropic glutamate receptor subtype 7-gene polymorphism and treatment response to methylphenidate, children with the G/A genotype had a more pronounced response rate than children with the G/G genotype .