Lecture 15: Neuropsychiatry and the Gut Microbiota 2

Question 1

Which tools are used to study genetic basis of disease?

Answer 1

genome wide association studies and exome sequencing of parents / affected patients / unaffected siblings

Question 2

What do genome wide association studies tend to miss?

Answer 2

rare, high impact mutations

Question 3

When does exome sequencing work best?

Answer 3

if you have the whole triad of parents, affected patients and unaffected siblings

Question 4

What does exome sequencing of parents / affected patients / unaffected siblings identify?

Answer 4

copy number variations, single nucleotide polymorphisms (SNPs), within gene deletions

Question 5

What do protein-protein interactions show?

Answer 5

strong overlap between diseases

Question 6

What does each gene cluster produce?

Answer 6

proteins with related functions

Question 7

What happens once a mutation has been identified?

Answer 7

generate an animal model expressing the mutation identified by sequencing and test its behaviour to see if that behaviour mimics what is seen in humans with the mutation

Question 8

What happens if the animal mutation behaviour does mimic what is seen in humans with the mutation?

Answer 8

test the physiological and neural circuit changes that might underline the alterations in behaviour and then generate animals models in which the relevant proteins are up- or down-regulated to begin to determine the function of the protein

Question 9

What are some examples of biological models?

Answer 9

cultures expressing the mutant gene to identify changes in cell biology produced by the mutation
zebrafish much more complex with a vertebrate CNS, but relatively easy to manipulate and short breeding and embryogenesis cycle

Question 10

What must an animal model have to be really useful?

Answer 10

construct validity, face validity and predictive validity

Question 11

What is construct validity?

Answer 11

expresses the mutation implicated in the genetic studies

in the same or equivalent locations

Question 12

What is face validity?

Answer 12

exhibit behaviours considered characteristic of the disease

in the case of ASD: aggression, stereotyped behaviour and abnormal communication

Question 13

What is predictive validity?

Answer 13

treatments that change behaviour in the model should produce similar outcomes in human patients

Question 14

What are problems with mouse models?

Answer 14

human brain is much more complex
predictions about the results of treatment made from rodent studies usually fail in humans when applied to brain disorders
the lifestyle of laboratory mice is very different from even the most confined of humans

Question 15

Which proteins are commonly mutated in ASDs?

Answer 15

synaptic proteins of which their central role is maintaining synapse function (neuroligin-neurexin)

Question 16

What is ASD associated with?

Answer 16

up to 90% of ASD patients reported to have GI dysfunction, notably constipation

Question 17

What complicates interpretation of ASD gut issues?

Answer 17

ASD patients are often very selective in what they will eat

Question 18

What might cause constipation in ASD patients?

Answer 18

ASD patients might engage in “faecal withholding”

changes in ENS function might parallel changes in CNS function

Question 19

Are all mutations relevant to ENS?

Answer 19

no, some mutations might not present in the ENS and proteins that regulate spine morphogenesis may have alternative functions in the ENS

Question 20

Why are neuroligins and neurexins relevant?

Answer 20

ASD-causing mutations in these genes would be expressed in ENS
mutations causing other neuropsychiatric diseases would also be expressed

Question 21

Why is neuroligin 3 important?

Answer 21

two mutations in neuroligin 3 produce ASD

1: gene deletion
2: point mutation that substitutes a cysteine for an arginine at position 451 in protein

Question 22

What neurons do NL3 R451C mice have more of in comparison to their wild type litter mates?

Answer 22

more myenteric neurons and more nitric oxide synthase neurons in jejunum

Question 23

Does ENS development differ between NL3 R451C mice and their wild type litter mates?

Answer 23

yes and this may be expected to have functional consequences

Question 24

What are the consequences of altered ENS development in NL3 R451C mice?

Answer 24

small intestinal transit in vivo is accelerated in these mice
weight of caecum is reduced and associated with altered lymphoid tissue in caecum

Question 25

Does the faecal microbiome in 5 week old NL3 R451C mice differ from wild type? What does this mean?

Answer 25

yes, this means that mutations in synaptic proteins that lead to ASD produce GI dysfunction