Neurocognitive deficits are assumed to be underlying the behavioral symptoms of ADHD. Research over the years has identified a host of these neurocognitive deficits, but no single one deficit appears to be dominant or pervasive in all ADHD children. This raises the query whether there can be further subgrouping of ADHD children at the neurocognitive level.

This study aims at disentangling the heterogeneous neurocognitive deficits underlying ADHD. To achieve this, we explore if there are separable neurocognitive subgroups in ADHD children.

One hundred and sixty-four Chinese ADHD boys and 163 typically developing controls, aged 6 to 12, were recruited in Hong Kong. A neurocognitive battery of executive function (EF) measures was administered. Cluster analysis was first conducted to identify subgroups of ADHD children based on their neurocognitive functioning. MANOVA was then employed to further explore the differences between subgroups.

Two ADHD subgroups were identified. One subgroup showed multiple EF deficits, including disinhibition, impaired interference control, distorted temporal information processing, slow processing speed, and delay aversion. The other subgroup, on the contrary, had intact EF but increased response variability. Both subgroups had comparable ADHD phenotypic severity and comorbidity pattern. However, ADHD children in the EF deficits subgroup were more responsive to medication (i.e., methylphenidate).

Results support the neurocognitive heterogeneity of ADHD. EF deficits and response variability are two separable neurocognitive profiles underlying and subgrouping ADHD children of comparable severity. This subgrouping has implication for medication response and offers candidate endophenotypes for neuroimaging and genetic study.

The authors have not supplied their declaration of competing interest.