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.

R.M.M. has received honoraria for lectures from Janssen, Lundbeck, Lilly, Otsuka and Sunovian.

Numerous studies have reported neuropsychological impairment in schizophrenia and increasing evidence suggests that individuals with schizophrenia or schizophrenia spectrum disorders and their unaffected first-degree family members exhibit similar deficits in some neuropsychological domains. Substantial modifications to the Wechsler Memory Scale (WMS) have resulted in more sensitive and reliable indicators of various aspects of memory functioning in the WMS-III, which enables generation of auditory, visual and working memory indices.

The aim of the present study was to examine the memory profile of individuals with schizophrenia or schizophrenia spectrum disorder (n = 19), their unaffected first-degree family members (n = 11), and healthy controls (n = 9).

The study involved neuropsychological testing, including the immediate and working memory subtests of the WMS-III, utilizing both auditory and visual domains. Symptom assessment was performed using the Schedules for Clinical Assessment in Neuropsychiatry (SCAN), version 2.0. Two multivariate analyses of covariance (mancova) were conducted: (i) comparing patients, relatives and controls; and (ii) comparing relatives and controls only.

The first analysis indicated that the patient group obtained significantly lower index scores than both relatives and controls on all three indices. The second analysis indicated that the performance of relatives was significantly lower than controls on the working memory index, although there were no significant differences on the auditory and visual immediate index scores.

The differential impairment in working memory performance in clinically asymptomatic family members suggests that the WMS-III working memory index score may be a potential phenotypic marker of schizophrenia.

Recent evidence points to partially shared genetics of neuropsychiatric disorders.

We examined risk of intellectual disability and other neuropsychiatric outcomes in 3174 children of mothers with schizophrenia, bipolar disorder or unipolar major depression compared with 3129 children of unaffected mothers.

We used record linkage across Western Australian population-based registers. The contribution of obstetric factors to risk of intellectual disability was assessed.

Children were at significantly increased risk of intellectual disability with odds ratios (ORs) of 3.2 (95% CI 1.8–5.7), 3.1 (95% CI 1.9–4.9) and 2.9 (95% CI 1.8–4.7) in the maternal schizophrenia, bipolar disorder and unipolar depression groups respectively. Multivariate analysis suggests familial and obstetric factors may contribute independently to the risk. Although summated labour/delivery complications (OR = 1.4, 95% CI 1.0–2.0) just failed to reach significance, neonatal encephalopathy (OR = 7.7, 95% CI 3.0–20.2) and fetal distress (OR = 1.8, 95% CI 1.1–2.7) were independent significant predictors. Rates of rare syndromes in children of mothers with mental disorder were well above population rates. Risk of pervasive developmental disorders, including autism, was significantly elevated for children of mothers with bipolar disorder. Risk of epilepsy was doubled for children of mothers with unipolar depression.

Our findings provide epidemiological support for clustering of neuropsychiatric disorders. Further larger epidemiological studies are warranted.

The epidemiology of intellectual disability co-occurring with schizophrenia and other psychiatric illness is poorly understood. The separation of mental health from intellectual disability services has led to a serious underestimation of the prevalence of dual diagnosis, with clinicians ill-equipped to treat affected individuals.

To estimate the prevalence of dual diagnosis and describe its clinical profile.

The Western Australian population-based psychiatric and intellectual disability registers were cross-linked (total n=245 749).

Overall, 31.7% of people with an intellectual disability had a psychiatric disorder; 1.8% of people with a psychiatric illness had an intellectual disability. Schizophrenia, but not bipolar disorder and unipolar depression, was greatly overrepresented among individuals with a dual diagnosis: depending on birth cohort, 3.7–5.2% of those with intellectual disability had co-occurring schizophrenia. Pervasive developmental disorder was identified through the Intellectual Disability Register and is therefore limited to individuals with intellectual impairment. None the less, pervasive developmental disorder was more common among people with a dual diagnosis than among individuals with intellectual disability alone. Down syndrome was much less prevalent among individuals with a dual diagnosis despite being the most predominant cause of intellectual disability. Individuals with a dual diagnosis had higher mortality rates and were more disabled than those with psychiatric illness alone.

The facility to combine records across administrative jurisdictions has enhanced our understanding of the epidemiology of dual diagnosis, its clinical manifestations and aetiological implications. In particular, our results are suggestive of a common pathogenesis in intellectual disability co-occurring with schizophrenia.