Causes of Disease

Question 1

What are the two types of causes of disease ?

Answer 1

Extrinsic and Intrinsic

• Extrinsic - from outside
• Intrinsic - from inside

The terms intrinsic and extrinsic can be ambiguous

• causes of disease are often a chain of events
  i. e. are allergies caused by a sensitive immune system (intrinsic) or the preceding allergen (extrinsic)
• Diseases can have a single cause, or be the product of multiple factors. E.g. Huntington’s disease caused by inheriting one of the CAG repeats

Question 2

Define Etiology

Answer 2

The initial events that caused the disease

Question 3

Define idiopathic

Answer 3

Conditions with no known cause are called idiopathic

Question 4

What are sporadic diseases ?

Answer 4

Crop up seemingly at random with no obvious cause

Question 5

What are some intrinsic causes ?

Answer 5

these are changes in an individuals genome

• Nuclear or mitochondrial
• inherited mutations and other genetic variations (i.e. chromosomal abnormalities)
• De novo mutations (occur from new)
• Epigenetic modifications (chemical methylation of DNA // methylation; phosphorylation or acetylation of histones)

Typically alter the function of a gene (or group of genes)
-e.g. more / less protein or same amount but more / less activity

Question 6

What are some effects of the intrinsic causes

Answer 6

Effects of genetic variations can manifest at a variety of levels

• Cell autonomously
  mutation effects the cell in which the protein is expressed
  ‘Cell X no longer expresses structural protein Y, so cell X is the wrong shape’
• Cell non-autonomously
  mutation effects a different cell to that which the protein is expressed / secreted
  ‘Cell X no longer secretes protein hormone Y, so cell Z no longer functions’

Question 7

What are some extrinsic causes ?

Answer 7

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

Question 8

Is age a cause of disease ?

Answer 8

age is a contributing factor to many diseases and really just means ‘time’.

Time increases cartilage damage thus increasing risk of osteoarthritis
Time also increases the number of mutations thus increasing risk of cancer

Age can be an intrinsic cause

e.g. Ageing –> menopause –> decreased estrogen –> risk of osteoporosis

many diseases associated with chronic inflammation also have a biological ageing as a cause

Question 9

What can intrinsic and extrinsic sometimes be categorised as ?

Answer 9

Genetic and Environmental

Question 10

Some examples of intrinsic disease

Answer 10

- Cancer 
Leukaemia, Lymphoma, Myeloma, Breast, prostate)
-Developmental diseases 
neural tube defects
-Inherited anaemia 
sickle cell disease, beta-thalassaemia
-Inherited metabolic diseases
phenylketonuria

Question 11

Down syndrome

Answer 11

Trisomy of chromosome 21
inherited at conception
intrinsic

Question 12

COVID-19

Answer 12

infection with SARS-coV-2

extrinsic

Question 13

some causes of lung cancer (are they extrinsic or intrinsic)

Answer 13

Extrinsic : 
Smoking tobacco 
chemicals and workplace risks
air pollution
exposure to radon gas 

Intrinsic (but with own causes)
previous lung disease

Intrinsic :
family history of lung cancer

Question 14

What are mitogens ?

Answer 14

Mitogens are substances that trigger the process of mitosis. Frequently, mitogens are proteins - compounds consisting of amino acid molecules that facilitate biochemical reactions in organisms