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Executive dysfunctions have been studied as a potential endophenotype associated with the genetic basis of autism. Given that recent findings from clinical and molecular genetic studies suggest that autism and obsessive-compulsive disorder (OCD) could share a common pattern of heritability, we assessed executive functions as a possible common cognitive endophenotype in unaffected family members of individuals with either autism or OCD.
Five tests assessing executive functions (Tower of London, verbal fluency, design fluency, trail making and association fluency) were proposed to 58 unaffected first-degree relatives (parents and siblings) of probands with autism and 64 unaffected first-degree relatives of OCD patients. Results were compared with those of 47 healthy controls matched for age, sex, and level of education.
In the Tower of London test, both groups of unaffected relatives showed significantly lower scores and longer response times compared with controls. No differences were observed between autism and OCD relatives and healthy controls in the four other tasks (verbal fluency, design fluency, trail making test and association fluency).
Our findings show the existence of executive dysfunction in the unaffected first-degree relatives of probands with OCD, similar to those observed in the relatives of patients with autism. These results support and extend previous cognitive studies on probands indicating executive dysfunctions in autism and OCD. Planning and working memory processes could thus represent a common cognitive endophenotype in autism and OCD that could help in the identification of genes conferring vulnerability to these disorders.
Progress in identifying the genetic vulnerability factors in autism requires correct identification of the inherited phenotype(s). This can be achieved not only by the accurate description of the affected subject but also by the identification of vulnerability traits in non-affected relatives of autistic probands. This review will focus on this last strategy and principally on clinical, biochemical and cognitive traits.
Background. Failure to resist chronic obsessive–compulsive symptoms may denote an altered state of cognitive control. We searched for the cerebral regions engaged in this dysfunction.
Method. Differences in brain regional activity were examined by event-related functional magnetic regional imaging (fMRI) in a group of adolescents or young adults (n=12) with childhood-onset obsessive–compulsive disorder (OCD), relative to healthy subjects. Subjects performed a conflict task involving the presentation of two consecutive and possibly conflicting prime and target numbers. Patients' image dataset was further analysed according to resistance or non-resistance to symptoms during the scans.
Results. Using volume correction based on a priori hypotheses, an exploratory analysis revealed that, within the prime-target repetition condition, the OCD subjects activated more than healthy subjects a subregion of the anterior cingulate gyrus and the left parietal lobe. Furthermore, compared with ‘resistant’ patients, the ‘non-resistant’ OCD subjects activated a bilateral network including the precuneus, pulvinar and paracentral lobules.
Conclusions. Higher regional activations suggest an abnormal amplification process in OCD subjects during the discrimination of repetitive visual stimuli. The regional distribution of functional changes may vary with the patients' ability to resist obsessions.
Background. Age at onset (AAO) has been useful to explore the clinical, neurobiological and genetic heterogeneity of obsessive–compulsive disorder (OCD). However, none of the various thresholds of AAO used in previous studies have been validated, and it remains an unproven notion that AAO is a marker for different subtypes of OCD. If AAO is a clinical indicator of different biological subtypes, then subgroups based on distinct AAOs should have separate normal distributions as well as different clinical characteristics.
Method. Admixture analysis was used to determine the best-fitting model for the observed AAO of 161 OCD patients.
Results. The observed distribution of AAO in OCD is a mixture of two Gaussian distributions with mean ages of 11·1±4·1 and 23·5±11·1 years. The first distribution, defined by early-onset OCD, had increased frequency of Tourette's syndrome and increased family history of OCD. The second distribution, defined by late-onset OCD, showed elevated prevalence of general anxiety disorder and major depressive disorder.
Conclusions. These results, based on a statistically validated AAO cut-off and those of previous studies on AAO in OCD, suggest that AAO is a crucial phenotypic characteristic in understanding the genetic basis of this disorder.
Objective: To evaluate sleep and alertness and to investigate the presence of possible
underlying sleep/wake disorders in children with attention-deficit/hyperactivity disorder
(ADHD). Method: After 3 nights of adaptation in a room reserved for sleep studies in the
department of child psychiatry, children underwent polysomnography (PSG) followed by the
Multiple Sleep Latency Test (MSLT) and reaction time tests (RT) during the daytime. Thirty
boys diagnosed as having ADHD (DSM-IV), aged between 5 and 10 years, and 22 age-
and sex-matched controls participated in the study. All children were medication-free
and showed no clinical signs of sleep and alertness problems. Results: No significant
differences in sleep variables were found between boys with ADHD and controls. The mean
latency period was shorter in children with ADHD. Significant differences were found for
MSLT 1, 2 and 3 (p<.05). Mean reaction time was longer in children with ADHD, with
significant differences in all tests (p<.05). Number and duration of sleep onsets measured
by the MSLT correlated significantly with the hyperactivity-impulsivity and inattentive-
passivity indices of the CTRS and CPRS. Conclusion: Children with ADHD were more
sleepy during the day, as shown by the MSLT, and they had longer reaction times. These
differences are not due to alteration in the quality of nocturnal sleep. The number of daytime
sleep onsets and the rapidity of sleep-onsets measured as MSLT were found to be pertinent
physiological indices to discriminate between ADHD subtypes. These results suggest that
children with ADHD have a deficit in alertness. Whether this deficit is primary or not
requires further studies.
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