It is hypothesized, that local retinoic acid (RA) homeostasis is functionally involved in the pathophysiology of depression. In a cross-sectional (and partly longitudinal) analysis, serum RA status will be assessed in healthy controls and subjects with Major Depression, Alzheimer's disease, alcoholism and in subjects with schizophrenia.

Retinoids comprise of a group of small-molecule derivatives of Vitamin A with retinoic acid (RA) representing the biologically most active endogenous form. RA has multiple functions central nervous system (CNS). It is hypothesized, that local RA homeostasis is functionally involved in the pathophysiology of numerous neuropsychiatric diseases.

MDD-Group

Inclusion Criteria:

• depressive episode in the context of unipolar major depression
• at least 18 points or more on the BDI and HAMD-17

Exclusion Criteria:

• additional or comorbid axis-I or axis-II disorder
• current history of any neurological or other serious medical condition
• any psychopharmacological treatment or substance use within the last two weeks or 5 half-lives (whichever is longer) of the respective substance
• any oral or topical application of retinoid-containing preparations within the last 3 months

AD-Group

Inclusion Criteria:

• diagnosed AD

Exclusion Criteria:

• any other neurodegenerative disorder
• any oral or topical application of retinoid-containing preparations within the last 3 months

Schizophrenia-Group

Inclusion Criteria:

• subjects with schizophrenia
• intended therapy with clozapine, olanzapine or aripiprazole
• BMI: 18 - 29,9 kg/m2

Exclusion Criteria:

• presence of diabetes or pathological glucose tolerance
• presence of and chronic inflammatory disease
• any psychopharmacological treatment of clozapine, olanzapine or aripiprazole within the last 3 months
• any oral or topical application of retinoid-containing preparations within the last 3 months

Alcoholism-Group

Inclusion Criteria:

• subjects with alcoholism who either still consume alcohol or are abstinent for at least 4 weeks

Exclusion Criteria:

• any oral or topical application of retinoid-containing preparations within the last 3 months
• current history of any neurological or other serious medical condition despite liver diseases

Out- and inpatients are eligible and will be recruited from patients seeking medical treatment at the Department of Psychiatry, Campus Benjamin Franklin, Charité, University Medicine Berlin.