Heritability of Trail Making Test performance in multiplex schizophrenia families: implications for the search for an endophenotype

A family study on first episode of psychosis patients: Exploring neuropsychological performance as an endophenotype

INTRODUCTION

Family studies provide a suitable approach to analyzing candidate endophenotypes of schizophrenia, including cognitive features.

OBJECTIVE

To characterize different neurocognitive functions in a group of patients with first episode of psychosis (FEP), their first-degree relatives (parents and siblings), and healthy controls (HC), in order to identify potential endophenotypes for schizophrenia spectrum disorders (SSD).

METHODS

Participants were assessed in the context of a national project in Spain called PAFIP-FAMILIAS. They completed the same neuropsychological battery, which included tests of verbal memory, visual memory, processing speed, working memory, executive functions, motor dexterity, attention, and theory of mind. Group comparisons were performed using one-way ANOVA, followed by tests of multiple comparisons when appropriate.

RESULTS

One hundred thirty-three FEP patients were included, as well as 244 of their first-degree relatives (146 parents and 98 siblings) and 202 HC. In general, relatives showed an intermediate performance between the HC and the FEP patients in all neurocognitive domains. However, the domains of executive functions and attention stood out, as relatives (especially parents) showed similar performance to FEP patients. This was replicated when selecting patients subsequently diagnosed with schizophrenia and their relatives.

CONCLUSION

These findings suggest that executive and attention dysfunctions might have a family aggregation and could be relevant cognitive endophenotypes for psychotic disorders. The study shows the potential of exploring intra-family neuropsychological performance supporting neurobiological and genetic research in SSD.

Schizotypal traits, neurocognition, and paternal age in unaffected first degree relatives of patients with familial or sporadic schizophrenia

Studies comparing cognitive processes between familial and sporadic schizophrenia have yielded inconsistent findings. In this study we examined differences in neurocognition and schizotypal traits in unaffected relatives of schizophrenia-spectrum patients with either the familial (multiplex) or the sporadic (simplex) subtype of the disorder, taking paternal age at birth into consideration. Simplex (n = 65; SR), multiplex (n = 35; MR) relatives and controls (n = 114) were compared on several cognitive functions and schizotypal traits; between-group differences were evaluated with and without including paternal age in the analyses. SR and MR had higher negative and paranoid traits compared with controls, but paternal age abolished the differences between the SR and control groups. When taking into account schizotypal traits and participants' age, controls outperformed MR in strategy formation and set-shifting and SR in psychomotor speed, set-shifting and executive working memory. After including paternal age in the analyses, controls outperformed MR in strategy formation, working memory and executive working memory and both groups in psychomotor speed and set-shifting. These findings suggest that multiplex relatives present with a "riskier" personality and cognitive profile when considering the effects of paternal age. Nevertheless, simplex relatives are impaired in fundamental cognitive processes, thus highlighting the detrimental effects of paternal age on neurocognition.

Executive function and genetic loading in nonpsychotic relatives of schizophrenia patients

Executive functions meet the "endophenotype candidate" criteria in neuropsychological measures for schizophrenic patients. To determine which area of executive functioning has the greatest value in differentiating the so called "candidate endophenotype" of schizophrenia through comparing the effect sizes of four commonly used executive function tests. A Wisconsin Card Sorting Test, a Stroop Test, a Trail Making Test and a Verbal Fluency Test were used to evaluate executive function in two study groups: healthy relatives of schizophrenia patients from simplex and multiplex families and a healthy control group. In all four tests, study groups performed poorly in contrast to the control group. In the B time, A error and B error results of the Trail Making Test, the multiplex group performed poorly compared to the simplex group; control group did better than both study groups. Our findings support that the presence of a schizophrenia patient in a family predicts worse performance on executive function tests in a group of healthy relatives of that individual. The results of our study suggest that the Trail Making Test in particular may signify a stronger endophenotypic trait.

Dopaminergic gene polymorphisms and cognitive function in a north Indian schizophrenia cohort

BACKGROUND

Associations of polymorphisms from dopaminergic neurotransmitter pathway genes have mostly been reported in Caucasian ancestry schizophrenia (SZ) samples. As studies investigating single SNPs with SZ have been inconsistent, more detailed analyses utilizing multiple SNPs with the diagnostic phenotype as well as cognitive function may be more informative. Therefore, these analyses were conducted in a north Indian sample.

METHODS

Indian SZ case-parent trios (n = 601 families); unscreened controls (n = 468) and an independent set of 118 trio families were analyzed. Representative SNPs in the Dopamine D3 receptor (DRD3), dopamine transporter (SLC6A3), vesicular monoamine transporter 2 (SLC18A2), catechol-o-methyltransferase (COMT) and dopamine beta-hydroxylase (DBH) were genotyped using SNaPshot/SNPlex assays (n = 59 SNPs). The Trail Making Test (TMT) was administered to a subset of the sample (n = 260 cases and n = 302 parents).

RESULTS

Eight SNPs were nominally associated with SZ in either case-control or family based analyses (p < 0.05, rs7631540 and rs2046496 in DRD3; rs363399 and rs10082463 in SLC18A2; rs4680, rs4646315 and rs9332377 in COMT). rs6271 at DBH was associated in both analyses. Haplotypes of DRD3 SNPs incorporating rs7631540-rs2134655-rs3773678-rs324030-rs6280-rs905568 showed suggestive associations in both case-parent and trio samples. At SLC18A2, rs10082463 was nominally associated with psychomotor performance and rs363285 with executive functions using the TMT but did not withstand multiple corrections.

CONCLUSIONS

Suggestive associations with dopaminergic genes were detected in this study, but convincing links between dopaminergic polymorphisms and SZ or cognitive function were not observed.

Neuregulin 3 is associated with attention deficits in schizophrenia and bipolar disorder

Linkage and fine mapping studies have established that the neuregulin 3 gene (NRG3) is a susceptibility locus for schizophrenia. Association studies of this disorder have implicated NRG3 variants in both psychotic symptoms and attention performance. Psychotic symptoms and cognitive deficits are also frequent features of bipolar disorder. The aims of the present study were to extend analysis of the association between NRG3 and psychotic symptoms and attention in schizophrenia and to determine whether these associations also apply to bipolar disorder. A total of 358 patients with schizophrenia and 111 patients with bipolar disorder were included. Psychotic symptoms were evaluated using the Operational Criteria Checklist for Psychotic Illness (OPCRIT) and attention performance was assessed using the Trail Making Test (TMT). Symptoms and performance scores were then tested for association with the NRG3 variant rs6584400. A significant association was found between the number of rs6584400 minor alleles and the total OPCRIT score for psychotic symptoms in patients with schizophrenia. Moreover, in both schizophrenia and bipolar disorder patients, minor allele carriers of rs6584400 outperformed homozygous major allele carriers in the TMT. The results suggest that rs6584400 is associated with psychotic symptoms and attention performance in schizophrenia. The finding of a significant association between rs6584400 and attention performance in bipolar disorder supports the hypothesis that this NRG3 variant confers genetic susceptibility to cognitive deficits in both schizophrenia and bipolar disorder.

[Schizophrenia and/or bipolar disorder: the neurocognitive endophenotypes]

Although Kraepelinian dichotomous conceptualization of psychosis was historically beneficial, modern studies do not support the existence of a sub-typing of psychotic illnesses into schizophrenic and affective psychoses. Years of intensive investigation on the genetic bases of schizophrenia and bipolar disorder suggest that these disorders, rather than being wholly distinct disorders, share common genetic risks. However, one of the most serious difficulties for genetic research in these illnesses is their enormous phenotypic heterogeneity. A response to this problem is the use of neurocognitive functions as endophenotypes or intermediate phenotypes. A review of the literature suggests that in both schizophrenia and bipolar disorder, neurocognitive functions are influenced by genetic factors and that there exists neuropsychological deficits in the nonaffected relatives of probands. However, it is unclear whether or not patterns of performance on neurocognitive tasks across probands as well as unaffected family members offer potential for identifying shared and illness-specific neurocognitive phenotypes for schizophrenia and bipolar disorder. Overlapping and unique neurocognitive endophenotypic signatures of the two psychoses are comprehensively described.

Prefrontal deviations in function but not volume are putative endophenotypes for schizophrenia

This study sought to systematically investigate whether prefrontal cortex grey matter volume reductions are valid endophenotypes for schizophrenia, specifically investigating their presence in unaffected relatives, heritability, genetic overlap with the disorder itself and finally to contrast their performance on these criteria with putative neuropsychological indices of prefrontal functioning. We used a combined twin and family design and examined four prefrontal cortical regions of interest. Superior and inferior regions were significantly smaller in patients. However, the volumes of these same regions were normal in unaffected relatives and therefore, we could confirm that such deficits were not due to familial effects. Volumes of the prefrontal and orbital cortices were, however, moderately heritable, but neither shared a genetic overlap with schizophrenia. Total prefrontal cortical volume reductions shared a significant unique environmental overlap with the disorder, suggesting that the reductions were not familial. In contrast, prefrontal (executive) functioning deficits were present in the unaffected relatives, were moderately heritable and shared a substantial genetic overlap with liability to schizophrenia. These results suggest that the well recognized prefrontal volume reductions are not related to the same familial influences that increase schizophrenia liability and instead may be attributable to illness related biological changes or indeed confounded by illness trajectory, chronicity, medication or substance abuse, or in fact a combination of some or all of them.

Neuropsychological performance and auditory event related potentials in schizophrenia patients and their siblings: a family study

BACKGROUND

Various neuropsychological domains, and P300 auditory event-related potentials (ERP) and mismatch negativity (MMN) exhibit abnormalities in schizophrenia patients and their first-degree relatives. The aims of this study were to compare cognitive and P300/MMN measurements in schizophrenia patients, their siblings, and controls, and to identify the degree of familial influence on each measure.

METHODS

Thirty patients diagnosed with schizophrenia according to DSM-IV, 20 unaffected siblings and 25 healthy controls were able to complete all neuropsyhological and neurophysiological assessments. All participants were administered SCID-I and the patients were also evaluated regarding symptom severity and functioning. Neuropsychological battery testing results and P300/MMN measurements were obtained for all the participants.

RESULTS

Both schizophrenia patients and their siblings had lower working memory, as measured by the Auditory Consonant Trigram Test (ACT), and lower MMN amplitude scores than the controls. In addition, the patients had lower attention, verbal memory, executive function, visuomotor speed, and figural memory scores than both the siblings and controls, and lower verbal fluency scores than controls. MMN and P300 amplitudes were lower and P300 latency longer in the schizophrenia patients, as compared to controls. P300 latency was also longer in the schizophrenia patients as compared to siblings and, MMN amplitudes were significantly lower in the siblings compared to controls. Working memory performance measured by ACT significantly predicted inclusion in both the patient and sibling groups and showed significant familial influence. MMN amplitude significantly predicted inclusion only to the patient group and did not show significant familial influence.

CONCLUSION

The schizophrenia patients exhibited impairment in various cognitive domains and P300/MMN measurements, versus impairment only in working memory and MMN amplitude in their siblings. Working memory seems to have a relatively strong familial influence among all the neuropsychological and neurophysiological parameters evaluated.

Genetic overlap between schizophrenia and selective components of executive function

Impairments in selective components of executive function are seen in unaffected family members of patients with schizophrenia and may represent the biological expression of increased genetic risk. However no study has quantified the extent to which liability to schizophrenia overlaps genetically with that of executive dysfunction. We studied a total of 418 monozygotic and dizygotic twins, including pairs concordant and discordant for schizophrenia. Participants completed the trail making test part A and verbal fluency tasks to assess initiation, TMT part B to test mental flexibility, and the WAIS-III to assess general intellectual function. Bivariate genetic modeling was used to investigate whether selective measures of executive processing are genetically linked to schizophrenia and to quantify the genetic (i.e. heritability) and environmental contributions to their variability. Genetic influences contributed substantially to test variance for initiation and mental flexibility. Genetic factors were the main source of the phenotypic correlations between schizophrenia and these processes. Verbal fluency tasks shared a large genetic correlation with IQ whilst TMT scales did not, suggesting that they measure discreet processes, and therefore indexing discreet endophenotypes. Both verbal fluency and mental flexibility meet some of the criteria for endophenotypes, but our data suggest that mental flexibility is a purer cognitive process sharing very little common variance with general intellectual functioning. The inclusion of this mental flexibility phenotype in linkage or association analysis should improve the power to detect susceptibility genes for schizophrenia.

Longitudinal alterations of executive function in non-psychotic adolescents at familial risk for schizophrenia

Genetic diathesis to schizophrenia may involve alterations of adolescent neurodevelopment manifesting as cognitive deficits. Brain regions mediating executive function (fronto-striatal circuits) develop during adolescence while those supporting elementary aspects of attention (e.g. sustained focused attention) have a more protracted maturation beginning in childhood. We hence predicted that adolescents at risk for schizophrenia would show a failure of normal maturation of executive function. We prospectively assessed 18 offspring and 6 siblings of schizophrenia patients (HR) and 28 healthy controls at baseline, year-1 and year-2 follow-up using the Continuous Performance Test [visual-d'] and Wisconsin Card Sort Test (WCST). Perseverative errors on the WCST in HR remained stable but decreased in controls over the follow-up (study-group by assessment-time interaction, p=0.01, controlling for IQ). No significant study-group by assessment-time interactions were seen for sustained attentional performance. HR may not improve while healthy subjects progressively improve on executive function during adolescence and early adulthood. Our results suggest an altered maturational trajectory of executive function during adolescence in individuals at familial risk for schizophrenia.