Biological 2) Genetic Predisposition

Question 1

Family Studies

Answer 1

Notes occurrence of ASD is family members.
1st degree- share 50% of genes.
2nd degree - share 25%.
Concordance rate represents proportion of pairs of relatives that have disorder.
If there is a genetic basis - higher concordance rate in 1st degree.

Question 2

Twin Studies

Answer 2

MZ - identical.
DZ - non-identical.
Takes advantage of naturally occurring genetic differences between twins.
If concordance rate is higher for MZ twins, genetic factors are implicated.

Question 3

Szatmari

Answer 3

Combined data from several family studies to calculate the over all sibling risk.
Risk was 2.2%.
Corresponding rate for no siblings is 0.11%.
20 times greater risk of having ASD is sibling has it.

Question 4

Bailey et al.

Answer 4

Analysed data from British Twin society.
Concordance rate for MZ was 60%, 0% for DZ.
Broadened scope - found 92% concordance rate for MZ, 10% for DZ.

Question 5

Ritvo et al.

Answer 5

Environment and upbringing have an influence as well as genetics.

Question 6

Incomplete Explanation

Answer 6

Twins studies can’t rule out environmental factors.
Diathesis-stress model proposed ASD is caused by interaction of genetic predisposition with an early damaging “insult” to the developing brain.
Genes don’t offer a complete explanation.

Question 7

Complexity

Answer 7

Researchers claim about 90% of ASD is caused by multiple genes interacting with each other and with environmental factors.
So complex that there is no convincing genetic explanation. for majority of ASD cases.