Explanations of Autism Individual Differences

Biological Explanations Individual Differences

Biological Explanations There are two main biological explanations for autism: -  Genetics.  Neurological Correlates.

Genetics Individual Differences

Genetic Explanations Evidence comes from four main areas: -  Family Studies.  Gender Differences.  Twin Studies.  Specific Chromosome/Gene Analysis.

Family Studies Folstein and Piven (1991) found 2-3% concordance rate for siblings of an autistic child (compared to 0.6% for general population).

Task 1 – Folstein and Piven (1991) Write a conclusion for Folstein and Piven’s study onto your handout (i.e. how does it support a genetic influence for autism?)…

Gender Differences Autism is four times more likely to occur in boys than girls.

Task 2 – Gender Differences Explain how the fact that boys are four times more likely to suffer from autism than girls supports a genetic influence.

Twin Studies Evidence comes from a variety of studies including: -  Rivto et al. (1985);  Folstein and Rutter (1977).

Rivto et al. (1985) Studied 23 pairs of identical (MZ) twins and 17 pairs of non-identical (DZ) twins. One twin of each pair had autism. Found 96% concordance between MZ twins (22/23) and 23% concordance between DZ twins (4/17). The higher rate of concordance in the MZ twins indicates that autism may have a genetic component.

Task 3 – Rivto et al. (1985) Explain why a higher rate of concordance in MZ twins than DZ twins indicates that autism may have a genetic component.

Task 4 – Folstein and Rutter (1977) Folstein and Rutter’s study has got mixed up. Copy the correct statement onto your handout under the headings aim,method, results and conclusion… Add to your conclusion why the study indicates that autism may have a genetic component.

Folstein and Rutter (1977) Found 36% concordance between MZ twins (4/11) and 0% concordance between DZ twins (0/10). When broadened to include milder signs of autism (autistic spectrum) they found 90% concordance between MZ twins. The higher rate of concordance in the MZ twins indicates that autism may have a genetic component. Studied 21 same-sex pairs of twins (11 MZ and 10 DZ). One of each twin pair had autism. Ppts were aged between Investigated whether autism had a genetic basis.

Specific Chromosome/Gene Analysis Studies involve comparing chromosomes of affected and unaffected family members. Frith (2003) noted that several large studies have identified sites on 4 chromosomes (2, 6, 15 and 16) as being involved. Roder (2000) has suggested that the HOSA1 gene may have a role in causing autism.

Genetic Explanations: Conclusion Carson at al. (2000) reviewed family and twin studies and found 80-90% of the variance in risk for autism is based on genetic factors, but the exact mode of genetic transmission is not yet understood.

Task 5 – Evaluation Copy the following evaluative statements in a table of strengths and weaknesses…

Genetic Explanations: Evaluation Twin studies suggest a strong genetic basis. Twins share same environment and therefore similarities may be the result of similar environments rather than genetic similarity. Autism has been associated with other genetic disorders, such as Tourette’s syndrome. They share many symptoms such as ritualistic behaviour, adherence to routine and stereotypical movements (Comings and Comings, 1991).

Genetic Explanations: Evaluation Chromosome analysis studies inconclusive. Discovering a gene/genes which cause autism may have ethical consequences (i.e. antenatal screening leading to couples choosing not have an autistic child). Low sample sizes in twin studies so one pair has large effect upon concordance rates. DZ twins and siblings are 50% genetically alike but have different concordance rates (23% v 2%). Supports environmental influence.

Task 6 – Homework! Complete the ‘Hyper and Hypo Sensitivity in Autism’ worksheet.