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PSYC20006 Biological Psychology > Behavioural & Psychiatric Genetics > Flashcards

Behavioural & Psychiatric Genetics Flashcards

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1
Q

Define a monogenic disorder.

A

A monogenic (‘single gene’) disorder is a disorder, the origins of which can be traced back to a single gene.

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2
Q

List a monogenic disorder or two.

A

Examples of a monogenic disorder would be ‘Fragile X Syndrome’ (FMR1), and ‘Huntington’s disease’ (HT).

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3
Q

Fragile X syndrome. What is it caused by?

A

FXS results from a copy-number variant in the 5’-untranslated region of the gene FMR1. FMR1 is critical to synaptic plasticity.

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4
Q

What does the 5’-untranslated region of a gene contain?

A

This region contains the ‘promotor region’, where chemicals bind to start the process of transcribing a gene into a protein.

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5
Q

Fill in the blanks: The expansion of ______ sequence of bases triggers _______.

A

The expansion of repeated CGG sequence of bases triggers methylation.

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6
Q

What does methylation do?

A

Methylation constricts the X chromosome and causes ‘fragile’ appearance.

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7
Q

Describe what the methylated promoter region does.

A

The methylated promoter region prevents transcription of the gene.

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8
Q

Define a polygenic disorder.

A

A polygenic (‘more than one gene’) disorder is a disorder, the origins of which can be traced back to/caused by several genes.

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9
Q

What does GWAS stand for?

A

Genome-Wide Association Studies.

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10
Q

What are GWAS used for?

A

Genome-Wide Association Studies (GWAS) are used to measure psychiatric disorders, psychological traits and cognitive traits.

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11
Q

What do GWAS examine?

A

GWAS examine the statistical association between a phenotype and many SNP markers throughout the genome, typically around 500,000 to 2,000,000 markers.

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12
Q

What is linkage disequilibrium?

A

Linkage disequilibrium (LD) is the correlation between two different SNPs.

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13
Q

True or False: There is no single gene for schizophrenia, autism, bipolar disorder, depression or anxiety.

A

True.

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14
Q

Why can we sample common variation sparsely (in a thinly dispersed manner; in small numbers)?

A

Because linkage disequilibrium (LD) allows us to observe indirect associations, chromosomes are mosaics and many variants are correlated.

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15
Q

What happens in a direct association?

A

The phenotype has a functional association with a non-genotyped SNP that is in LD with a genotyped SNP.

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16
Q

What is an allelic dosage model used for?

A

For quantatitive traits.

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17
Q

What is an allelic association model used for?

A

Categorical and binary traits.

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18
Q

What does a manhattan plot do?

A

Graphically summarises the results of all of our individual tests of association.

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19
Q

What does each point on a manhattan plot represent?

A

The outcome of a test for one SNP.

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20
Q

What is on the horizontal axis on a manhattan plot?

A

Physical location on the genome and within a chromosome.

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21
Q

What is on the vertical axis of a manhattan plot?

A

Transformed p value, lower p values are higher on the axis, emphasising the strongest associations.

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22
Q

Why are thresholds for significance stringent?

A

Because multiple comparisons increase the likelihood of Type 1 error.

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23
Q

What are the thresholds for significance typically set at?

A

Typically set around α = 5 x 10-8 (p

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24
Q

What does that threshold for significance correspond to?

A

The Bonferroni correction for around 1 million independent (uncorrelated) tests.

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25
Q

What does imputation predict?

A

Genotypes at non-genotyped SNPs.

26
Q

What does imputation rely on?

A

On data from a reference panel of individuals genotyped at high density.

27
Q

What patterns does imputation apply?

A

Applies patterns of linkage disequilibrium discovered in the reference panel.

28
Q

What does genetic distance and recombination rate reflect?

A

The frequency with which two markers are inherited together, helps define the region likely to contain the functional variant.

29
Q

What does conservation indicate?

A

The extent to which a sequence is maintained across species.

30
Q

What does high conservation suggest?

A

An important function preserved during evolution

31
Q

What can ‘skyscrapers’ be explained by?

A

Multiple SNPs in linkage disequilibrium with a functional SNP, multiple functional SNPs in the same gene.

32
Q

What did a meta-analysis of bipolar disorder GWAS find?

A

Found an association with the ANK3 and CACNA1C genes.

33
Q

What do the proteins transcribed from both of these gene regulate?

A

The flow of ions in and out of neurons during an action potential.

34
Q

What are both the genes down-regulated by?

A

Lithium.

35
Q

What does lithium do to the proteins?

A

Lithium reduces transcription of the protein.

36
Q

What is lithium an effective treatment of?

A

Bipolar disorder (BP).

37
Q

“Strong correlation between the sample size of a GWAS and…” (finish the sentence)

What does this mean?

A

Strong correlation between the sample size of a GWAS and the number of associated markers discovered.

This means that larger samples provide more statistical power to detect small effects.

38
Q

What are one of the things GWAS can do?

A

GWAS can provide new evidence for existing hypotheses.

39
Q

In regards to schizophrenia, how has GWAS provided new evidence for existing hypotheses?

A

Schizophrenia has previously been linked to abnormal dopamine signalling, antipsychotic drugs block dopamine receptors. DRD2, a dopamine-receptor gene, is associated with schizophrenia

40
Q

What is another thing GWAS can do?

A

GWAS can raise new possibilities regarding understanding of behavioural and psychiatric genetics.

41
Q

How has GWAS raised new possibilities?

A

GWAS has posited that the most significant association is the histocompatibility complex (MHC), MHC genes code for cell-surface proteins that allow the immune system to recognise foreign substances.

42
Q

What is the last thing studies that GWAS can do?

A

GWAS can point out environmental factors regarding understanding of behavioural and psychiatric genetics.

43
Q

How has GWAS pointed out environmental factors?

A

GWAS has posited that variants in the CHRNA5-A3-B4 gene cluster are known to be very strongly associated with heavy smoking. Encode subunits of a nicotine acetylcholine receptor, cholinergic receptors that also response to nicotine. Association of schizophrenia with CHRNA5-A3-B4 variants suggests heavy smoking may contribute to schizophrenia.

44
Q

What do disorders consist of?

A

Complex GxE (Gene x Environment) interactions, diagnostic categories, measurement problems, interference from multiple deficits.

45
Q

What do endophenotypes consist of?

A

More immediate relationships, single quantitative traits, psychologically normal participants.

46
Q

What is an endophenotype?

A

A quantitative biological trait that reflects the function of a discrete biological system and is reasonably heritable.

47
Q

What is a cognitive measure of endophenotypes?

A

The Wisconsin Card Sorting test.

48
Q

What does the Wisconsin card sorting test involve?

A

Sort cards according to one rule, then having this rule change.

49
Q

What are neurophysiological measures of endophenotypes?

A

Pre-pulse inhibition of startle response.

50
Q

What is a psychomotor measure of endophenotypes?

A

The antisaccade oculomotor task.

51
Q

What does the antisaccade motor task involve?

A

Watching a dot and look in the opposite direction of its movement when it moves.

52
Q

What are some examples of endophenotypes?

A

Anomalies of basic visual perception, disturbances of visual sensitivity are associated with both schizophrenia and autism.

53
Q

What did they find in a GWAS of visual sensitivity in a psychologically healthy population?

A

The strongest association signal was at a marker on chromosome 1q21.1

54
Q

Where is the marker situated?

A

The 5’-untranslated region of the gene PDZK1

55
Q

What does the 5’-untranslated region contain?

A

The promotor region

56
Q

What happens if the functional SNP is situated in the 5’-untranslated region?

A

It likely affects protein transcription rather than protein structure

57
Q

What do PDZ proteins do?

A

They hold other proteins in appropriate configuration for localisation on the surface of cells

58
Q

What are the interactions between PDZK1 and NMDA receptors?

A

NMDA receptors play a critical role in contrast gain control in the retina, perceptual abnormalities in schizophrenia have been suggested to arise from NMDA receptor dysfunction

59
Q

What are the interactions between PDZK1 and DLG4?

A

Disruption of Dlg4 in a mouse results in an ASD-related phenotype

60
Q

What is the difference between DLG4 and Dlg4?

A

Human genes are all capital, rodent genes are title case

61
Q

What may perceptual abnormalities observed in two different disorders be linked by?

A

Common genetic elements that affect synaptic function

62
Q

How can endophenotypes of psychological disorders yield larger genetic effects than diagnoses?

A

Avoids difficulties assigning diagnostic categories, allows testing of psychologically normal participants, underlying biological mechanisms are likely to be simpler than for psychological disorders

PSYC20006 Biological Psychology (16 decks)

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