GRIN2B and attention deficit-hyperactivity disorder: For example, a recent study showed that the genetic variants of N-methyl-d-aspartate receptor subunit-encoding genes (GRIN2A and GRIN2B) confer an increased susceptibility to attentional impairment measured by CPT in ADHD patients [40]; a genome-wide association study of CPT performance in adults with ADHD reported 27 suggestive loci were associated with CPT outcomes [41], implying that CPT deficits might be helpful in detecting genetic etiology of ADHD.