Inclusion criteria:

For inclusion in the study subjects must fulfil all of the following criteria:

1. Provision of written informed consent
2. A diagnosis of schizophrenia by Diagnostic and Statistical Manual of Mental Disorders- Fourth Edition (DSM-IV)
3. Able to understand and comply with the requirements of the study
4. Age 18 - 65 years

Exclusion criteria:

Any of the following is regarded as a criterion for exclusion from the study:

1. Any DSM-IV Axis I disorder not defined in the inclusion criteria
2. Patients who, in the opinion of the investigator, pose an imminent risk of suicide or a danger to self or others
3. Known intolerance or lack of response to quetiapine fumarate, as judged by the investigator
4. Use of any of the following cytochrome P450 3A4 inhibitors in the 14 days preceding enrolment including but not limited to: ketoconazole, itraconazole, fluconazole, erythromycin, clarithromycin, troleandomycin, indinavir, nelfinavir, ritonavir, fluvoxamine and saquinavir
5. Use of any of the following cytochrome P450 inducers in the 14 days preceding enrollment including but not limited to: phenytoin, carbamazepine, barbiturates, rifampin, St. John's Wort, and glucocorticoids
6. Administration of a depot antipsychotic injection within one dosing interval (for the depot) before inclusion
7. Substance or alcohol dependence at enrolment (except dependence in full remission, and except for caffeine or nicotine dependence), as defined by DSM-IV criteria
8. Opiates, amphetamine, barbiturate, cocaine, cannabis, or hallucinogen abuse by DSM-IV criteria within 4 weeks prior to enrolment
9. Medical conditions that would affect absorption, distribution, metabolism, or excretion of study treatment
10. Unstable or inadequately treated medical illness (e.g. diabetes, angina pectoris, hypertension) as judged by the investigator
11. Involvement in the planning and conduct of the study
12. Previous enrolment in the present study.
13. Participation in another drug trial within 4 weeks prior enrolment into this study or longer in accordance with local requirements
14. Actual treatment with clozapine or clozapine treatment during the previous three month. Other antipsychotic drugs will be allowed, if intake can be terminated during the two day wash out period.
15. Previous history of major head injuries or neurological disorders
16. Intake of homocysteine lowering vitamins (folate, B12, B6)
17. Renal failure
18. Intake of nutritional derivatives which influence epigenetic patterns (butyrate from milk products, tea polyphenol or epigallo-catechin-3-gallate which inhibits DNMT)