Aims:

Associations are consistently seen between cigarette use and psychosis, although direction of causation is not known. There is also a large body of literature showing cognitive impairment in patients with schizophrenia. There has been some suggestion that high rates of smoking in schizophrenia could be to alleviate cognitive impairment from both the disorder and anti-psychotic medication side-effects, as nicotine has been posited as a cognitive enhancer. We aim to investigate whether associations between cigarette use, cognition and psychotic experiences are causal, using Mendelian Randomisation.

Hypotheses:

As these are exploratory analyses, we do not have hypotheses as to what we will find in terms of causality.

Exposure variables:

Genetic instruments as proxy variables for cigarette use and for risk of schizophrenia.

Outcome variables:

Cognitive tasks at age 18, smoking at age 18, psychotic experiences at age 18 (all measured at clinic).

Confounding variables:

As this is a Mendelian randomisation design, the analyses should not be subject to the usual confounders that impact upon observational studies. However, gender and ethnicity will be accounted for in our analyses. Data on confounders has been requested to check for pleiotropy.