Unit 6: Intelligence

This week's class focused on the genetics of intelligence.  This unit was very interesting to me because Joshua's deletion (and most chromosomal deletions where the child is missing millions of bases) can potentially have some effect on cognitive ability.  It was encouraging to learn that intelligence is one of the main areas where environment, and not just genes, can play a big role.  Here are the notes from this week's class:

Definition of Intelligence -

• to understand and use complex ideas
• to adapt effectively to the environment
• to learn from experience
• to engage in abstract reasoning

Is intelligence one thing or many things (and what should be emphasized)?

• Verbal ability
• Numerical ability
• Spacial ability
• Mechanical ability

How does your performance in one area predict your peformance on other types of abilities?

• Could be positively associated, negatively associated, or unrelated.
• Performance on multiple ability tests are always positively correlated, so it implies something common across the 4 tests - your General Cognitive Ability.  
• "General Cognitive Ability" - general intelligence - your performance across the 4
• The absence of perfect correlation does show that they are distinct abilities.

IQ Test

• IQ test samples your skills in multiple intellectual domains and summarizes it in a  number.  
• IQ is a measure of general cognitive ability.  
• Average IQ is 100.  2/3rds of population fall between 85-115.  2.5% below 70, 2.3% above 130.  

What do twin & adoption studies show about the contribution of genetics and environment to intelligence?

• Genetics:  50% heritable
• Shared environment:  35%
• Non-shared environment:  15%
• So, both genetics and environment play an important part in intelligence.  

Gene Environment Interplay

• Average IQs in population have increased 3-5 points per decade in the last several decades.
• Better public health, better public schools
• Adoption studies show that children who were adopted (v. siblings who were not) tend to score much higher in both IQ and school achievement.
• Adoption in general (not just compared to biological siblings) is correlated with higher IQ and higher school achievement, because in general it means a shift to a more advantaged home.
• This is true in working, middle, and professional class homes - but greater benefits as the socioeconomic class goes up.  
• Heritability of GCA is diminished in poor and working class homes.
• This is because in wealthier homes, kids get opportunities which allow them to fully realize their genetic potential; in less wealthy homes, kids don't get these same opportunities and therefore do not always realize their full genetic potential.

Genetic Factors

• Total brain volume is highly heritable.
• Total brain volume is associated with GCA, but probably not the best way to measure GCA.
• Common genetic factors contribute to brain volume and GCA.
• Researchers have not had much success yet in identifying which genes are most highly associated with GCA.  
• Using a genome wide study, they found places on Chromosome 1, 2, and 6, that were correlated with how far students went in school - but extremely small effects.  (consistent with schizophrenia, height, etc.)

Genetics of Intellectual Disability

• What is intellectual disability?
• IQ less than 70. AND
• Deficit in intellectual functioning results in impairments in adaptive functioning AND
• Onset in child
• Implications of the non-normal distribution of IQ
• More individuals with intellectual disability than we would expect with normal distribution.
• 90% of individuals with intellectual disability have mild disability - can live independently but require some assistance; 
• There's 6x greater population of moderate intellectual disability than we would expect, and 6,000x greater population of profound intellectual disability than we would expect.
• Two groups
• Single major trauma - can be genetic, perinatal trauma, etc. (5-10% of all individuals with intellectual disability)
• Due to cumulative impact of many small factors (90-95%, usually the more mild disability, this is who would be expected on the bell curve)
• Males are at higher risk for intellectual disability than females
• 40-50% more likely
• X-linked intellectual disability is a major factor
• Males only have one X chromosome so only require one hit; since females have two X chromosomes, would need two mutations to be affected.  
• Secondly, males are biologically more vulnerable than females - eg, higher mortality rate at all ages, more vulnerable to consequences of low birth weight and birth trauma, higher risk for most neurodevelopmental disorders.  
• Study found that females with intellectual disability have a higher load of genetic risk factors than males affected with intellectual disability.