Allelic variation in the gene encoding brain-derived neurotrophic factor (BDNF) has been associated with affective disorders, but generally not schizophrenia. Brain-derived neurotrophic factor variants may help clarify the status of schizoaffective disorder.

To test the hypothesis that BDNF haplotypes are associated with psychiatric illness marked by a prominent affective component.

Frequencies of a 5-marker BDNF haplotype were examined in 600 White participants across four diagnostic categories and healthy controls.

Individuals with schizoaffective disorder and other affective disorders were significantly more likely to carry two copies of the most common BDNF haplotype (containing the valine allele of the Val66Met polymorphism) compared with healthy volunteers. Moreover, when compared with people with schizophrenia, individuals with schizoaffective disorder were significantly more likely to carry two copies of the common haplotype.

To our knowledge, this is the first candidate gene study to demonstrate association with schizoaffective disorder but not schizophrenia. Variation in the BDNF gene may be associated with the clinical phenotype of affective dysregulation across several DSM–IV diagnostic categories.

Despite the high prevalence of cannabis use in schizophrenia, few studies have examined the potential relationship between cannabis exposure and brain structural abnormalities in schizophrenia.

To investigate prefrontal grey and white matter regions in patients experiencing a first episode of schizophrenia with an additional diagnosis of cannabis use or dependence (n=20) compared with similar patients with no cannabis use (n=31) and healthy volunteers (n=56).

Volumes of the superior frontal gyrus, anterior cingulate gyrus and orbital frontal lobe were outlined manually from contiguous magnetic resonance images and automatically segmented into grey and white matter.

Patients who used cannabis had less anterior cingulate grey matter compared with both patients who did not use cannabis and healthy volunteers.

A defect in the anterior cingulate is associated with a history of cannabis use among patients experiencing a first episode of schizophrenia and could have a role in poor decision-making and in choosing more risky outcomes.

Studies have shown increased bilateral activation in the prefrontal cortex when normal individuals lie, but there have been no structural imaging studies of deceitful individuals.

To assess whether deceitful individuals show structural abnormalities in prefrontal grey and white matter volume.

Prefrontal grey and white matter volumes were assessed using structural magnetic resonance imaging in 12 individuals who pathologically lie, cheat and deceive (‘liars’), 16 antisocial controls and 21 normal controls.

Liars showed a 22–26% increase in prefrontal white matter and a 36–42% reduction in prefrontal grey/white ratios compared with both antisocial controls and normal controls.

These findings provide the first evidence of a structural brain deficit in liars, they implicate the prefrontal cortex as an important (but not sole) component in the neural circuitry underlying lying and provide an initial neurobiological correlate of a deceitful personality.