Biological explanation - genetic predisposition

Question 1

What does this explanation state?

Answer 1

• states that those with AD have a genetic predisposition to the disorder
  family studies and twin studies are used to investigate

Question 2

Family and twin studies

Answer 2

Szatmari (1999) combined data from several family studies to calculate the sibling risk - risk was found to be 2.2%
Bailey et al (1995) analysed data from the british twin study
- concordance rate for MZ twins was 60% and DZ twins was 0%
- the researchers then widened the definition of autistic behaviours to include other characteristics and found 92% concordance for MZ` AND 10% for DZ

Ritvo et al found concordance rates of 96% for MZ twins and 23% for DZ twins

Question 3

Simplex or multiplex

Answer 3

• in some families only 1 member has ASD known as simplex ASD
• in multiplex ASD families, either more than one member has a diagnosis of ASD or several have autistic traits

it is thought that the mechanism of genetic vulnerability differs in simplex and multiplex families
multiplex - ASD is caused by genetic variations that are inherited
simplex - new genetic mutations occur when sequences of the DNA are duplicated at fertilisation
- affects multiple genes which are called copy number variations (CVNS)

CNVs account for 10% of all diagnosed case of ASD

Question 4

Syndromic and non syndromic

Answer 4

ASD can be diagnosed on its own which is known as non syndromic and it is unclear what the underlying genetic cause is
- ASD can be syndromic, meaning it accompanies another biological condition, that is the the main disorder
- this other condition may also have a well established genetic cause

Question 5

Syndromic comorbidity rates for ASD and ADHD

Answer 5

• Studies show that between 30 and 50% of individuals with ASD have ADHD symptoms (particularly at pre-school age
• similarly 2/3rds of individuals with ADHD show features of ASD (Davis and Kollins, 2012)

Question 6

Evaluating Genetic explanations (A03)

Answer 6

Scientific - can be falsified, research can be objective and quantitative

Reductionist - easier to conduct scientific research due to high level of control but it tends to ignore strong evidence from the cognitive explanations and less robust evidence from psychodynamic approach

Deterministic - able to identify predisposing factors which allows for predictions to be made with potential help to develop appropriate therapies
- however this can lead to feelings of parental blame

Question 7

Evaluation

Answer 7

Benvenuto et al (2009) identified at least 10 candidate genes with various roles
- it is claimed that 90% of ASD is caused by multiple genes interacting with each other and other environmental factors
- this supports the genetic explanation for ASD because it shows how biological factors influence the development of ASD and the theory is seen to be correct

Question 8

Evidence against the genetic explanation of ASD

Answer 8

-Studies with a large number of families are underway to hunt for the predisposing genes for ASD
- however other additional factors can be looked over e.g
- problems may occur in early pregnancy
- certain viral infections of the mother during pregnancy are thought to be a risk factor
- low intake of the B vitamin folate
- Any unknown effect of a drug taken, that affects the brain during the pregnancy or early childhood
- toxic chemicals that the developing brain may be exposed to in early pregnancy e.g high level of air pollution

• these offer evidence against the genetic explanation as it may not just be genetics playing a role but how the child was developed during pregnancy and if any problems were seen to have occured