Can genetics inform the management of cognitive deficits in schizophrenia?

D2/D3 dopamine receptor binding with [F-18]fallypride correlates of executive function in medication-naïve patients with schizophrenia

Converging evidence indicates that the prefrontal cortex is critically involved in executive control and that executive dysfunction is implicated in schizophrenia. Reduced dopamine D2/D3 receptor binding potential has been reported in schizophrenia, and the correlations with neuropsychological test scores have been positive and negative for different tasks. The aim of this study was to examine the relation between dopamine D2/D3 receptor levels with frontal and temporal neurocognitive performance in schizophrenia. Resting-state ¹⁸F-fallypride positron emission tomography was performed on 20 medication-naïve and 5 previously medicated for brief earlier periods patients with schizophrenia and 19 age- and sex-matched healthy volunteers. Striatal and extra-striatal dopamine D2/D3 receptor levels were quantified as binding potential using fallypride imaging. Magnetic resonance images in standard Talairach position and segmented into gray and white matter were co-registered to the fallypride images, and the AFNI stereotaxic atlas was applied. Two neuropsychological tasks known to activate frontal and temporal lobe function were chosen, specifically the Wisconsin Card Sorting Test (WCST) and the California Verbal Learning Test (CVLT). Images of the correlation coefficient between fallypride binding and WCST and CVLT performance showed a negative correlation in contrast to positive correlations in healthy volunteers. The results of this study demonstrate that lower fallypride binding potential in patients with schizophrenia may be associated with better performance. Our findings are consistent with previous studies that failed to find cognitive improvements with typical dopamine-blocking medications.

Association of KIBRA rs17070145 polymorphism with episodic memory in the early stages of a human neurodevelopmental disorder

A common T/C polymorphism within the ninth intron of the KIBRA gene (rs17070145) is thought to influence memory in humans. Since cognitive impairment, including memory, is a core feature of schizophrenia, we attempted to investigate this association in an independent sample of adolescent patients with early-onset schizophrenia (EOS; onset before age 18) probands and their healthy siblings. In a sample of 25 pairs of EOS proband-healthy full sibling, we sought to investigate the association of KIBRA with memory performance. Episodic memory was measured using immediate and delayed recall measures of the California Verbal Learning Test. EOS underperformed at immediate and delayed recall compared with siblings. In a combined analysis (TT vs. TC/CC) assuming a C dominant model of inheritance, we found a main effect of genotype where individuals with TT genotype outperformed non-TT-carriers at immediate and delayed recall. A genotype by group interaction showed that EOS with TT genotype did not show a memory advantage over siblings with TT or non-TT-carriers at immediate or delayed recall. Siblings with TT genotype showed enhanced immediate recall (not delayed recall) compared with non-TT-carriers. This study demonstrates an association between the KIBRA gene and episodic memory (immediate free recall) and suggests a differential effect of this genetic variant in EOS and healthy siblings.

T102C polymorphism of serotonin-2A receptor gene in Turkish schizophrenia patients: Association with cognitive impairment and soft neurological signs

AIM

Previous studies have shown an association between the T102C polymorphism of the serotonin-2A receptor gene and schizophrenia. In addition, an association of this polymorphism with clinical phenotypes in schizophrenia such as treatment response and cognitive impairment has been observed.

MATERIALS AND METHODS

In this case-control study conducted in Turkish Caucasians, we compared T102C polymorphism genotype and allele frequencies in 76 schizophrenic patients and 165 healthy controls. We also investigated interaction of this polymorphism with clinical and cognitive variables in patients.

RESULTS

No significant difference was observed in the distribution of the three genotypes (T/T, T/C and C/C) and in the allele frequencies in controls and patients with schizophrenia. No evidence of association was detected at various clinical phenotypes including symptom severity, suicidality, treatment response, age of disease onset, number of hospitalizations and history of violence (in co-dominant, dominant, or recessive models). However, as compared to the C/C genotype, patients with 1 or 2 copies of the T allele were characterized by better stroop test performances and less "motor coordination" soft neurological signs.

CONCLUSION

Further research is needed to elucidate the impact of T102C polymorphism on neurocognitive functions in both healthy and patient populations.

Treatment of early onset schizophrenia: recent trends, challenges and future considerations

Early onset schizophrenia (onset before adulthood) is a rare, severe, and chronic form of schizophrenia. The clinical presentation of schizophrenia at this unusually early age of onset has been associated with premorbid developmental abnormalities, poor response to neuroleptic treatment, greater admission rates, and poor prognosis. This is a brief, condensed review of current treatment strategies for the early onset population highlighting the need for novel treatment strategies for these generally treatment-refractory cases. Based on the current literature, second-generation antipsychotics remain the mainstay of treatment, although current medications provide suboptimal response at best. Based on the adult literature, combining antipsychotic treatment with psychotherapeutic intervention may be a more comprehensive treatment strategy. Indeed, early detection, identification of relevant biomarkers, coupled with advancing knowledge of the neurochemical and neuroanatomic pathways may help design informed and novel treatment strategies.