Multifactorial Inheritance

Question 1

What are the properties of common complex diseases (multifactorial diseases)

Answer 1

They are multifactorial environmental and genetic causes

Polygenic (many genes are effected)

Question 2

Are they easy to identify inheritance patterns?

Answer 2

No
Some familial clustering suggesting some genes are involved but there is no obvious inheritance pattern
e.g. CHD
Breast and bowel cancer
Diabetes
hypetension

Question 3

How can you identify the environmental and the genetic causes of a diseases?
4 Studies?

Answer 3

Using observational studies

Familial clustering (is the incidence in a family higher than in a pop)

Twin studies
compare incidence between monozygotic (share all genes) and dizygotic (share 50%) and there environment
High concordance in MZ indicates a genetic component
Low concordance in MZ indicates low genetic component

Adoption studies
What is the incidence in adopted children of disorders there biological parents had

Population and migration studies
what is the incidence in people from a particular ancestral group when the move to a new geographical are

Question 4

What is polygenic inheritance

Answer 4

Many genetic factors and genes are involved each making an small additive contribution to overall phenotype

Question 5

What are the characteristics of multifactorial diseases?

Give some examples

Answer 5

They are polygenic
And usually only affect one organ system

e.g. diabetes mellitus
glaucoma
hypertension
CHD

Congenital hip dislocation
neural tube defects
cleft lip

Question 6

What is a liability curve?

Answer 6

Model that can be used

bell shaped curve poltted from genetic and environmental factors form population from which it was gathered

There is a theoretical threshold value above which the person develops the multifactorial condition

Question 7

What facors increase the probability of recurrence of. a multifactorial condition within family?

Answer 7

Close relationship to person with condition
severe and early onset of condition
multiple family members affected

Question 8

How are genes that are involved in common complex disorders identified?

Answer 8

Done through association studies in large populations

SNP’s used as genetic markers

test thousands of individuals with and without condition

compare SNP patterns looking to see if SNP patterns more common in own group

Relative risk generated if a person has a particular SNP associated with diseased group

Question 9

What is the benefit of finding out you have a predisposition?

Answer 9

Can change some environmental factors to reduce likelihood of developing disease