Revision

Question 1

What occurs during an acute enteroviral infection of beta cells?

Answer 1

The hosts antiviral response is impaired. The enterovirus establishes a lytic infection. There is rapid synthesis of large numbers of viral particles. Followingcell lysis, viral and beta cell specific antigensare released,triggering activation of islet autoreactive immune cells. There is some beta cell destruction but eventually the virus is cleared and this stops.

Question 2

What occurs during a persistent enteroviral infection of beta cells?

Answer 2

The hosts antiviral response is partially successful.There are deletions in the 5’ UTR of the viral genome leading to problems with replication.The virus produces equal amounts of +ve and -ve RNA strands, forming dsRNA.Presence of dsRNA activates pathogen recognition receptors such as Mda5 leading to enhanced IFN production. IFN upregulatesMHC I on beta cell surface leading to insulitis and autoimmune destruction of beta cells

Question 3

Why does detection of Mda5 and RIG-1 in beta cells indicate viral infection?

Answer 3

Mda5 and RIG-1 induce expression of IFNs (e.g. IFNalpha) in response to detection of viral dsRNA. Mda5 normally expressed only in alpha cells

Question 4

Describe the genome replication process of +ve ssRNA viruses

Answer 4

The viral +ve ssRNA is directly translated into proteins involved in genome replicaiton, such as RNA dependent RNA polymerase.

The +ve ssRNA is then recruited to viral replication complexes.

Formation of dsRNA intermediates.

Replication takes place in membrane invaginations to avoid dsRNA detection.

Question 5

How do thiazide diuretics work and what are the side effects?

Answer 5

Antagonists of the NCC cotransporter
E.g. chlorothiazide

Leads to increased potassium excretion in collecting duct (hypokalemia)
Increased excretion of hydrogen ions (metabolic alkalosis)
Hypercalcaemia

Question 6

How do loop diuretics work and what are the side effects?

Answer 6

Inhibitor of the NKCC2 cotransporter
E.g. Furosemide
Prevents formation of concentration gradient in the medulla, so less reabsorption of water in the collecting duct

Can also cause hypokalemia

Question 7

How does hypoaldosteronism lead to

1. Hyperkalemia
2. Hyperchloremia
3. Metabolic acidosis

Answer 7

1. Reduced Na+/K+ ATPase activity means reduced K+ excretion
2. Increased chloride reabsorption in the collecting duct
3. Increased chloride reabsorption leads to hyperchloremic acidosis

Question 8

What are the possible mutations that can lead to Gordon’s Hypertension Syndrome?

Answer 8

WNK1 - cannot be ubiquitinated
WNK4 - missense mutation in C terminal non-catalytic domain where KLHL3 would bind, so cannot be ubiquitinated
The BTB domain of KLHL3 - cannot interact with CUL3
CUL3 - cannot ubiquitinate WNK

All lead to gain of function in WNK1/4

Question 9

What are the implications of mutations in epigenetic proteins?

Answer 9

Global DNA hypomethylation can lead to activation of proto-oncogenes and genomic instability
Promoter hypermethylation can lead to silencing of tumour suppressor genes

Question 10

How can epigenetic processes be involved in cancer?

Answer 10

Mutations in epigenetic writers, readers and erasers - particularly DNMT3a and TET are mutated in blood cancers
Mutations in proteins in the chromatin remodelling complex
Methylated cytosines can become deaminated into guanine - major DNA sequence change

Question 11

How does histone acetylation lead to gene expression?

Answer 11

1. Reduced affinity of histone tail for adjacent nucleosomes
2. Removal of histone positive charge, DNA doesn’t bind as tightly
3. Recruitment of proteins with bromodomains, such as transcription factors and HAT

Question 12

How does DNA methylation lead to transcriptional silencing?

Answer 12

Inhibition of transcription factor binding, either directly or via altered histone acetylation.
Also attracts methyl binding proteins.

Question 13

How can transdifferentiation be used to create new beta cells?

Answer 13

Adult liver cells, such as alpha cells, can be transdifferentiated into beta cells by using a virus to deliver transcription factors to them such as PDX-1, Ngn3 and Mafa

Question 14

How can a patients own beta cells be regenerated?

Answer 14

Patients that still have some detectable levels of C-peptide have some remaining beta cells. Application of IGF-1, hepatocyte growth factor, adenosine agonists or GABA may increase their proliferation. Also the fasting-mimicking diet may promote proliferation.

Question 15

Describe 3 ‘amplifying pathways’ that regulate insulin secretion independently of glucose

Answer 15

Fatty acids metabolised by krebs cycle to produce ATP, close channels…
Also bind to cell surface receptor GPR40 which increases protein kinase C and A

GLP-1 hormone secreted by gut when eating, increases cAMP and PKA

Amino acids metabolised by krebs cycle, direct depolarisation of cell membrane

Question 16

How is insulin release controlled by the neural pathway?

Answer 16

PSNS secretes Ach, Ach binds a GPCR that activates phospholipase C, activation of protein kinase C promotes vesicle fusion

SNS secretes NA, NA binds adrenergic receptor that inhibits formation of cAMP, less protein kinase A leads to less vesicle fusion

Question 17

Name some sources of genetic variation

Answer 17

Chemical agents
UV radiation
Hydrolysis of bases
Deamination of methylated cytosine into uracil
Base pair mismatch during replication
Replication slippage
Recombination errors
Chromosome/chromatid segregation errors

Question 18

Why are DDDs difficult to diagnose?

Answer 18

1. High heterogeneity - large possible numbers of affected genes
2. Every genome has novel variation - which variation is disease causing?
3. Most genetic variation is benign, lots of variants to filter out
4. Similar phenotypes can be caused by different affected genes
5. Inheritance patterns can vary between diseases

Question 19

What are the uses of trio exome sequencing?

Answer 19

1. Exclusion of benign inherited variants
2. Highlights de novo mutations
3. Identification of homozygous or compound heterozygous variants
4. Identification of new disease genes

Question 20

If you have identified a de novo mutation in a child that you think might be disease causing, how could you prove this?

Answer 20

1. Show that individuals without the phenotype do not have the variant
2. Show that individuals with the phenotype have the variant (or have a different variant within the same gene)
3. Sequence genome of any affected/unaffected family members to see if they have the variant
4. Use in vitro or in vivo functional studies to find the effect of the variant e.g. animal models
5. Statistical methods such as enrichment analysis

Question 21

How is appetite controlled by neurons within the brain?

Answer 21

Neurons in the arcuate nucleus receive hormone signals and pass signals onto effect neurons
NPY/AGRP neurons project orexigenic signals
POMC/CARt neurons project anorexigenic signals

Question 22

What is the most common and severe type of monogenic obesity and how is it inherited?

Answer 22

Mutation in MC4R
Leads to loss of function or partial loss of function
Causes hyperphagia, hyperinsulinemia, increased lean mass
Codominant inheritance

Question 23

How can genetics influence the type of food we eat?

Answer 23

Certain variants in FGF21 increase affinity for
- snacking on sweet foods
- higher carbohydrate intake
- increased alcohol intake
Elevated fasting levels of FGF21 are associated with decreased affinity for sweet foods

Question 24

What is the cause of Prader-Willi syndrome?

Answer 24

Defect of a gene on chromosome 15 that is normally maternally imprinted. The paternal copy becomes deleted or two maternal copies are inherited. No functioning alleles of the gene.