© Banff and Buchan College 2004

Depression – Biological Factors

Mood Disorders

• Biological explanations– Genetics– Neurochemical abnormalities

Mood Disorders – Genetic

• Zubenko et al (2001)– Family history – 50% of FD relatives, 25% of SD

relatives also had mood disorder– Relatives had increased risk of suicide & liver

disease

• McGuffin et al (1996)– MZ 46%, DZ 20%– MZ concordances substantially inflated in more

serious cases

Mood Disorders – Genetic

• Depression tends to run in families

• The closer the relationship with a sufferer, the more likely a person will have a mood disorder

• Genetic evidence is strongest for most severe forms of the disorder

• Concordance rates also indicate a substantial environmental contribution

Mood Disorders - Neurochemical

• Abnormality in neurochemicals

• Too much or too little of some chemicals e.g. serotonin affects the functioning of the brain – this might have an effect on emotion regulation

Mood Disorders - Neurochemical

Mood Disorders - Neurochemical

• Noradrenanaline (NA)– Too little leads to depression, too much to mania

(catecholamine hypothesis)

• Serotonin (5-HT)– Regulates NA activity, so too little allows abnormal

fluctuations in NA (permissive amine hypothesis)

• Dopamine (DA)– Involved in reinforcement, so too little results in anhedonia

(dopamine hypothesis)

Mood Disorders - Neurochemical

• Some evidence (but not all) suggests that mood disorder patients have abnormal levels of NA & 5-HT– Might be sensitivity to neurotransmitters that

matters, not raw levels in brain– Interactions between neurotransmitters are

poorly understood – likely to be complex– Problems with direction of causality

Mood Disorders - Neurochemical

• Drugs that alter brain levels of NA & 5-HT are effective in treating depression in about 60% of cases– So what about the non-responsive patients?– Relapse when drugs are discontinued?– Treatment-aetiology fallacy?

© Banff and Buchan College 2004

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