Session 4b - Genetics of affective disorders Flashcards
The following studies will be looked at in this session:
Family, twin and adoption studies, models of transmission, sex differences, linkage/association, and new developments.
Enjoy! ;)
Homotypia can be unipolar (UP) and bipolar (BP) depression bread through. What is the general correlation of UP and BP in families.
In families of BP pro bands, there is an increase of BP and UP depression.
In families of UP pro bands, there is an increase of UP, but not of BP depression
(it was found that monozygotic/identical twins has an increased risk developing both UP and BP than dizygotic/un identical twins)
what is the lifetime risk of getting A) unipolar depression B) bipolar depression
5-15% - unipolar
0.5-1% - bipolar
Adoptees from depressed biological parents have an increased risk than from healthy biological parents. True or false?
True.
Revise MGD: genes, DNA,RNA, mitosis, meiosis, transcription, translation.
What is a gene?
What is meant by ‘genotype’ and ‘phenotype’?
A gene is part of a chromosome that can synthesise mRNA and thus a protein
Genotype: what the chromosome of an individual looks like.
Phenotype: what the individual looks like
There are two main forms of inheritance in affective disorder: (see reverse)
SML = single major locus with variable penetrance
X
QTL = Quantitative trait loci, which refers to loci that contribute significantly to the variation in quantitative traits in the population
Linkage & Association: these are methods for mapping disease loci. In linkage the co-occurance with a known disease and a known location is measured. Association reverse to the co-occurenc of an allele at a particular locus and a disease. What is meant by the terms ‘allele’ and ‘locus’?
What is a polymorphism?
allele - version of a gene
locus - the location of a particular gene on a given chromosome
Polymorphism - there are two or more alleles with a frequency of at least 1%
Linkage can be calculated into a LOD (log of the odds) score. What does a score of a) >3 and b)
> 3 means support for linkage
Association studies and depression: This is a two stage process. What are the two stages?
From this, what are 2 polymorphisms found with regards to depression?
What effects may these polymorphism have?
- systematic polymorphism detection
- ## association studies of disease comparison
- The serotonin transporter gene (Chrom 17). Altered response to SSRIs.
- The BDNF (brain derived neurotropic factor) gene (Chrom 11). Changes to childhood experiences and stressful events.
GWAS (genome wide association studies) focus on modern genetic studies in psychiatry. The genetic load of CNV (copy number variants) has been significant.
What is meant by CNV?
A copy number variation (CNV) is when the number of copies of a particular gene varies from one individual to the next. Following the completion of the Human Genome Project, it became apparent that the genome experiences gains and losses of genetic material.
Genetics and environment go hand in hand when predisposing someone to developing depression. In some cases the environment can alter DNA - what is this referred to as?
Epigenetic: relating to or arising from non-genetic influences on gene expression. (Can have epigenetic changes in response to childhood maltreatment (methylation))
Statistically, more female than males suffer from depression. Suggest a genetic reason for this?
Gene on the X chromosome may predispose woman to depression.
Protective gene found on the Y chromosome.
Describe the general summary of current thinking of depression and genetics.
About 50% of behaviour disorders due to genes (very rough estimate).
Complex genetic mechanisms with Quantitative Trait Loci (QTLs). Each QTL responsible for small amount of difference. A focus on traits rather than diagnosis.
