Objectives: Few studies have seized the opportunity to study the cognitive and neural base of ASD and ADHD in conjunction. Such an investigation, of a carefully selected clinically comorbid sample, could provide an excellent basis to identify pleiotropic genes for ASD and ADHD. The study could also serve as a basis for the investigation of evidence supporting a novel and distinct syndrome that manifests both phenotypes.We aimed to conduct such an investigation.
Methods: We established a large database of ASD probands (with and without co-occurring ADHD) (N=180). Evaluations were also made of affected and unaffected siblings, and parents. In addition we established a database of ADHD probands (N=400), also containing assessments of affected and unaffected siblings, and parents. A third database comprised control subjects and their siblings and parents. Probands, siblings and parents have been phenotyped for ASD and ADHD symptoms, and have been evaluated on a set of cognitive tests including face recognition, emotion recognition and prosody, working memory, inhibition and planning.
Results: We have started to analyse the data in terms of 3 questions: 1) which cognitive impairments are common to both ASD and ADHD and which are specific to ASD or ADHD ?; 2) do the cognitive impairments in ASD map onto one common underlying cognitive construct, or alternatively, do these impairments better fit into a 2- or 3-factor model; and 3) to which extent are these cognitive impairments familial in ASD, in ADHD, and in ASD and ADHD families ?
Conclusions: Results of these forthcoming analyses will provide further insight into the cognitive endophenotypes of ASD and ADHD. They will also provide insights into the nosological issue of whether, as least in a subset of cases, ASD and ADHD are different manifestations of one overarching disorder. These findings could provide evidence of a biological basis for recent observations that children from the general population with persistent hyperactive-inattentive symptoms are almost entirely subsumed within a subgroup of children with persistently impaired social-communication (St Pourcain et al, 2011). The implications of that observation are that children with persistent social communication impairments may comprise a heterogeneous clinical population, with distinct biological substrates underlying their superficially similar symptomatology. Our potential findings will have implications for the revision of rules in DSM-5 regarding the separate recording of ADHD-traits in the presence of an autistic spectrum disorder.