Multifactorial Inheritance

Question 1

What is a multifactorial inheritance:

Answer 1

Diseases due to a combination of genetic and environmental factors. Most common diseases are multifactorial.

Question 2

What are the traditional clinical genetic techniques:

Answer 2

Family, twin and adoption studies

Question 3

Explain family studies:

Answer 3

Compare the prevalence of disease amongst relatives of affected vs general population.
In MF:
- Risk of condition to relatives higher than general population
- Risk varies with degree of genetic relationship

Question 4

Explain twin studies:

Answer 4

Compare MZ genetically identical with DZ non genetically identical
In MF:
- Concordance rate % (both have) higher in monozygotic twins then dizygotic twins if genetic component

Question 5

Explain adoption studies:

Answer 5

Compare with group of adoptees w/ normal biological parents and parent w/condition
Adopted child with parent with MF condition have a higher risk of developing disease.

Question 6

Characteristics of MF:

Answer 6

• Incidence of condition greater amongst relatives of severely affected
• Risk greatest for 1st degree relatives, decreases rapidly further down

Question 7

What is liability threshold model ?

Answer 7

Factors influence MF - liability
Liabilities of individuals form a continuous variable w/ normal distribution
Relatives - Curve shifts to right compared to general population, closer relationship, shift to the right
Threshold - above this abnormal phenotype is expressed

Question 8

What is population and familial incidence?

Answer 8

• Population incidence - General population above threshold
• Familial incidence - Relatives above threshold

Question 9

What is neural tube defect?

Answer 9

Defective closure of developing neural tube during 1st month of embryonic life
Environmental factors include poor socioeconomic status, multiparity and valproate.

Question 10

Environmental Agents on Embryogenesis:

Answer 10

• Drugs and chemicals - thalidomide, alcohol
• Maternal infections - rubella, CMV
• Physical agents - radiation
• Maternal illness - diabetes, phenylketonuria

Question 11

Postnatal Environmental Factors:

Answer 11

• Obesity - type 2 diabetes
• Hormonal factors - breast cancer
• Smoking - lung cancer
• Recreational drugs - schizophrenia