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-caused by atherosclerosis
-family history of CAD = x2 to suffer from CAD than those without a family history of CAD.
-Risk is greater if affected person is female and if onset in relative occurred below age of 55.
- linked with genes encoding LDL receptor
-Heterozygosity for a mutation (1/500 individuals) and causes hypercholesterolemia.
-Environmental factors include, smoking, diet exercise.
i.e., hypertension.
Some traits do not follow a normal distribution and don’t follow the pattern for a single gene disorder.
Explained by a liability distribution.
Liability distribution:-
if at low end little chance of developing the disease
if at higher end have more disease causing genes and more environmental factors so at higher risk of that disease.
Means that a threshold of liability must be exceeded before a disease is expressed.
Causes vomiting, weight loss & electrolytic imbalance, treated by surgery.
Prevalence in Caucasian population – 3/1000 but incidence is 1/200 for males and 1/1000 for females.
Difference in incidence reflects a lower prevalence threshold in males and higher prevalence threshold in females.
Low prevalence threshold – fewer factors required cause diseaseAutosomal SGDs - 50% for dominant, 25% for recessive.
Multifactorial – more complex because number of genes contributing are unknown
Achieved by:-
a) Examining large number of families with proband(1st person in familia to receive genetic counselling for genetic disorder) .
b) Determining the % of relatives to develop the disease.
Example – Neural tube defects – in US, defects seen in 2-3% of proband siblings, so recurrence risk for parents with one affected child is 2-3%.
Empirical recurrence risk is disease specific.
Families, genes & a common environment, thus, family members may share common traits, i.e. hypertension.
Is this down to genetics or environment (nature or nurture).
Examined using:-
genetically identical
derived from two ova being fertilised, so genetically no more alike than any other siblings. DZ twins can have different fathers! Any differences due to genetics and environmental factors.
twins share the same trait
If a trait is entirely due to genetics MZ twins should be 100% concordant and DZ twins should be less concordant.
Concordance in DZ twins can vary between opposite sex and same sex twins for some traits.
twins do not share the same trait.
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