Olfactory identification performance in individuals with psychometrically-defined schizotypy

While deficits in olfaction have been well documented in individuals with schizophrenia, less research has focused on olfactory identification performance in psychometrically-defined schizotypy. The Abbreviated Schizotypal Personality Questionnaire was used to define two groups of 26 individuals (62% female) reporting high and average levels of schizotypy. Overall group differences on the Brief Smell Identification Test did not approach statistical significance, and this finding did not differ within either sex. The findings may reflect either the abbreviated nature of the measures used, or a lack of reliable olfactory performance differences in schizotypy.     

An auditory processing abnormality specific to liability for schizophrenia

Abnormal brain activity during the processing of simple sounds is evident in individuals with increased genetic liability for schizophrenia; however, the diagnostic specificity of these abnormalities has yet to be fully examined. Because recent evidence suggests that schizophrenia and bipolar disorder may share aspects of genetic etiology the present study was conducted to determine whether individuals with heightened genetic liability for each disorder manifested distinct neural abnormalities during auditory processing. Utilizing a dichotic listening paradigm, we assessed target tone discrimination and electrophysiological responses in schizophrenia patients, first-degree biological relatives of schizophrenia patients, bipolar disorder patients, first-degree biological relatives of bipolar patients and nonpsychiatric control participants. Schizophrenia patients and relatives of schizophrenia patients demonstrated reductions in an early neural response (i.e. N1) suggestive of deficient sensory registration of auditory stimuli. Bipolar patients and relatives of bipolar patients demonstrated no such abnormality. Both schizophrenia and bipolar patients failed to significantly augment N1 amplitude with attention. Schizophrenia patients also failed to show sensitivity of longer-latency neural processes (N2) to stimulus frequency suggesting a disorder specific deficit in stimulus classification. Only schizophrenia patients exhibited reduced target tone discrimination accuracy. Reduced N1 responses reflective of early auditory processing abnormalities are suggestive of a marker of genetic liability for schizophrenia and may serve as an endophenotype for the disorder.     

Brief Report: No Association Between Premorbid Adjustment in Adult-Onset Schizophrenia and Genetic Variation in Dysbindin

Whereas Dysbindin is considered a schizophrenia vulnerability gene, there is no consistency of findings. Phenotype refinement approaches may help to increase the genetic homogeneity and thus reconcile conflicting results. Premorbid adjustment (PMA) has been suggested to aid the phenotypic dissection. Gornick et al. (J Autism Dev Disord 35:831–838, 2005) reported an association between Dysbindin and PMA in US-Caucasian individuals with childhood-onset psychosis. In a sample of 222 adult-onset schizophrenia inpatients from Germany, we could not detect an association between PMA and 36 SNPs in Dysbindin. Our results suggest that genetic variation in Dysbindin may not contribute to the schizophrenia phenotype with an onset beyond childhood. Further studies including even larger samples and more SNPs may be warranted to clarify the relationship between Dysbindin and PMA.     

Brief Report: An Autistic Spectrum Subtype Revealed Through Familial Psychopathology Coupled with Cognition in ASD

This study identified a possible autistic spectrum subtype expressed through family psychopathology coupled with autistic probands’ cognitive functioning (i.e., an endophenotypic profile). Participants included 24 children with Autism Spectrum Disorder (ASD) and 49 children with Learning Disorder (LD). There were significantly higher rates of Mood and Anxiety Disorder in first degree maternal relatives and of LD and Attention-Deficit Hyperactivity Disorder in first degree paternal relatives of ASD probands. Significantly higher visuospatial functioning was noted in all ASD probands for which there were higher rates of Mood Disorder on the maternal side suggesting a possible marker for an ASD subtype and indicating that maternal psychopathology may have a neuroprotective effect on visuospatial functioning.     

Is the P3 amplitude reduction seen in externalizing psychopathology attributable to stimulus sequence effects?

P3 amplitude reduction (P3-AR) is associated with biological vulnerability to a spectrum of externalizing (EXT) disorders, such as conduct disorder, antisocial behavior, and substance use disorders. P3 amplitude, however, can be affected by the context within which it is measured, for example, by the position of the target in the sequence of stimuli during an oddball task. We hypothesized that EXT-related P3-AR may be due to attention or working memory deficits in EXT that would weaken these stimulus sequence effects. Using a community-based sample of adolescent males, we examined the relationship between P3 and EXT as a function of the number of standards preceding the target. Higher EXT was associated with significantly smaller P3 amplitude, regardless of the number of standards preceding the target. These results suggest that P3-AR in EXT does not vary as a function of stimulus sequence, further supporting P3-AR as an endophenotype for EXT disorders.     

Exploring the neurocognitive signature of poor set-shifting in anorexia and bulimia nervosa

Poor set-shifting has been implicated as a risk marker, maintenance factor and candidate endophenotype of eating disorders (ED). This study aimed to add clarity to the cognitive profile of set-shifting by examining the trait across ED subtypes, assessing whether it is a state or trait marker, and whether it runs in families. A battery of neuropsychological tasks was administered to 270 women with current anorexia (AN) and bulimia nervosa (BN), women recovered from AN, unaffected sisters of AN and BN probands, and healthy control women. Set-shifting was examined using both individual task scores and a composite variable (poor/intact/superior shifting) calculated from four neuropsychological tasks. Poor set-shifting was found at a higher rate in those with an ED particularly binge/purging subtypes. Some evidence for poor set-shifting was also present in those recovered from AN and in unaffected sisters of AN and BN. Clinically, poor set-shifting was associated with a longer duration of illness and more severe ED rituals but not body mass index. In sum, poor set-shifting is a transdiagnostic feature related to aspects of the illness but not to malnutrition. In part it is a familial trait, and is likely involved in the maintenance of the illness.     

Genetics of human prefrontal function

Evolution of the prefrontal cortex was an essential precursor to civilization. During the past decade, it became increasingly obvious that human prefrontal function is under substantial genetic control. In particular, heritability studies of frontal lobe-related neuropsychological function, electrophysiology and neuroimaging have greatly improved our insight. Moreover, the first genes that are relevant for prefrontal function such as catechol-O-methyltransferase (COMT) are currently discovered. In this review, we summarize the present knowledge on the genetics of human prefrontal function. For historical reasons, we discuss the genetics of prefrontal function within the broader concept of general cognitive ability (intelligence). Special emphasis is also given to methodological concerns that need to be addressed when conducting research on the genetics of prefrontal function in humans.