Causes of Disease

Question 1

What is aetiology? What does idiopathic refer to?

Answer 1

Aetiology refers to the causes of disease which can have a single cause or be a product of multiple factors
Conditions with no known cause are called idiopathic

Question 2

What does it mean when we refer to intrinsic causes of disease? Give some examples

Answer 2

= Changes in an individual’s genome
- Nuclear or mitochondrial
- Inherited mutations and other genetic variations
- de novo mutations
- Epigenetic modifications
Typically alter the function of a gene (or group of genes)
E.g. more/less protein or same amount but more/less activity

Question 3

What are the different levels effects of genetic variations can manifest at?

Answer 3

Cell autonomously:
- Cell X no longer expresses structural protein Y, so cell X is the wrong shape
Cell non-autonomously
- Cell X no longer secretes protein hormone Y, so cell Z no longer functions

Question 4

What are the extrinsic causes of disease?

Answer 4

Numerous!

- Injury
- Infection
- Nutrition and diet
- Lifestyle, e.g. smoking, exposure to workplace toxins
- Chemical poisoning (acute and chronic)
- Exposure to radiation

Question 5

What are the grey areas of the extrinsic and intrinsic classification system?

Answer 5

The terms intrinsic or extrinsic can be ambiguous
Causes of disease are often a chain of events
- Are allergies caused by a sensitive immune system (intrinsic) or the preceding allergen (extrinsic)?
Intrinsic or extrinsic depends on viewpoint,
i.e. extrinsic to what: cell, tissue, organ, body?
- Pay attention to the context!

Question 6

Which category of extrinsic/intrinsic does age fit into?

Answer 6

Age really just means ‘time’, in the context of causes that accumulate
Age can be an intrinsic cause when it describes the biological process of ageing
For example:
Many diseases associated with chronic inflammation also have a biological ageing as a cause

Question 7

Apply the intrinsic/extrinsic classification to Down’s syndrome and Covid-19

Answer 7

Cause of Down Syndrome
	Trisomy of chromosome 21, inherited at conception
	Intrinsic
Cause of COVID-19
	Infection with SARS-CoV-2
	Extrinsic