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There is increasing evidence for shared genetic susceptibility between schizophrenia and bipolar disorder. Although genetic variants only convey subtle increases in risk individually, their combination into a polygenic risk score constitutes a strong disease predictor.
To investigate whether schizophrenia and bipolar disorder polygenic risk scores can distinguish people with broadly defined psychosis and their unaffected relatives from controls.
Using the latest Psychiatric Genomics Consortium data, we calculated schizophrenia and bipolar disorder polygenic risk scores for 1168 people with psychosis, 552 unaffected relatives and 1472 controls.
Patients with broadly defined psychosis had dramatic increases in schizophrenia and bipolar polygenic risk scores, as did their relatives, albeit to a lesser degree. However, the accuracy of predictive models was modest.
Although polygenic risk scores are not ready for clinical use, it is hoped that as they are refined they could help towards risk reduction advice and early interventions for psychosis.
Declaration of interest
R.M.M. has received honoraria for lectures from Janssen, Lundbeck, Lilly, Otsuka and Sunovian.
Diffusion tensor magnetic resonance imaging studies in schizophrenia to
date have been largely inconsistent. This may reflect variation in
methodology, and the use of small samples with differing illness duration
and medication exposure.
To determine the extent and location of white matter microstructural
changes in schizophrenia, using optimised diffusion tensor imaging in a
large patient sample, and to consider the effects of illness duration and
Scans from 76 patients with schizophrenia and 76 matched controls were
used to compare fractional anisotropy, a measure of white matter
microstructural integrity, between the groups.
We found widespread clusters of reduced fractional anisotropy in
patients, affecting most major white matter tracts. These reductions did
not correlate with illness duration, and there was no difference between
age-matched chronically and briefly medicated patients.
The finding of widespread fractional anisotropy reductions in our larger
sample of patients with schizophrenia may explain some of the
inconsistent findings of previous, smaller studies.
Dimensional structures are established for many psychiatric diagnoses, but dimensions have not been compared between diagnostic groups.
To examine the structure of dimensions in psychosis, to analyse their correlations with disease characteristics and to assess the relative contribution of dimensions v. diagnosis in explaining these characteristics.
Factor analysis of the OPCRIT items of 191 Maudsley Family Study patients with schizophrenia, mood disorders with psychosis, schizoaffective disorder, and other psychotic illnesses, followed by regression of disease characteristics from factor scores and diagnosis.
Five factors were identified (mania, reality distortion, depression, disorganisation, negative); all were more variable in schizophrenia than in affective psychosis. Mania was the best discriminator between schizophrenia and affective psychosis; the negative factor was strongly correlated with poor premorbid functioning, insidious onset and worse course. Dimensions explained more of the disease characteristics than did diagnosis, but the explanatory power of the latter was also high.
Kraepelinian diagnostic categories suffice for understanding illness characteristics, but the use of dimensions adds substantial information.
Intellectual asymmetry with superiority of verbal skills to spatial skills
frequently characterises patients with schizophrenia, but it is unclear
whether this pattern also reflects genetic susceptibility to the disorder.
We examined the association of a continuous measure of genetic liability to
schizophrenia with Verbal-Spatial Contrast IQ (an index of intellectual
asymmetry) in 108 first-degree relatives without psychosis of probands with
schizophrenia. Higher genetic liability was significantly associated with
greater intellectual asymmetry in favour of verbal skills. Intellectual
asymmetry with a relative superiority of verbal skills to spatial skills
represents a putative endophenotype of schizophrenia.
We report cognitive performance of a group of individuals who are likely to have transmitted liability to psychosis to their offspring. Out of 230 relatives of patients with psychosis, 27 met our criteria for a presumed obligate carrier, that is a non-psychotic individual who had a parent or a sibling as well as an offspring with psychosis. The presumed obligate carriers showed impairments in verbal memory and in visuospatial manipulations, suggesting that these individuals transmit vulnerability for psychosis to their offspring in terms of a disability to recall verbal information and an impaired capacity to perceive spatial relations.
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