Genetic and Environmental Influences on Reading Ability and Disability (Difficulty)

Richard Olson, University of Colorado, Boulder

•Science Announces 2007 Breakthrough of the Year: Human Genetic Variation After years of research into genetic similarities among people and even apes, research advances on several fronts during 2007 defined the degree to which genomes differ from one human to another. This breakthrough represents a conceptual leap that allows discovery of individual risk for disease and specific medical treatment. Science recognized "Human Genetic Variation" as the leading breakthrough of 2007

•In 2007, researchers were dazzled by the degree to which genomes differ from one human to another and began to understand the role of these variations in disease and personal traits.

Colorado Learning Disabilities Difficulties Research Center (CLDRC)

• Twin Studies (Psychometric assessment) (John DeFries, Sally Wadsworth, Erik Willcutt)

• ADHD and executive function (Bruce Pennington, Erik Willcutt)

• DNA Linkage analysis and physical mapping (Shelley Smith)

• Response to Computer Assisted Reading Instruction (Barbara Wise, Brian Byrne, Ron Cole, Sarel van Vuuren)

• Reading and language processes (Jan Keenan, Richard Olson)

How do we know if a “personal trait” is influenced by genes?

• Because we have identified the responsible gene or genes from molecular genetic analyses?

• Because the trait runs in families?

• Because there are two kinds of twins.

Why Study Twins?

• Monozygotic (MZ) twins share 100% of all their genes

• Dizygotic (DZ) twins share 50% of their segregating genes (genes that make us different), on average

• MZ and DZ pairs reared together have similar shared environment in the home and school (assumption of analyses)

• (But, MZ twins may create more similar environments, such as print exposure, because of their genes, a

genotype-environment correlation

Twin Data Can Estimate Population Averages for Three Causes of Individual Differences:

Heritability (genes) : genetic influences.(does not tell us which genes or individuals)

Shared (Common) Environment : environmental influences that affect similarly both twins in a pair.(prenatal, home, school)

Nonshared Environment : environmental influences that are specific to individual twins.(accident, teacher, measurement error)

Population Mean

Our behavior-genetic analyses of twin data assume a normal distribution (the bell curve)

Low Reading High Reading

number

of

people

• Twins’ TOWRE Sight Word Efficiency Standard Scores

• at the End of First Grade

Such normal distributions allow us to estimate genetic and environmental

influences by comparing correlations for MZ and DZ twins

• So lets look at some correlations…

• Expected correlation for randomly paired individuals

P1

P2

T1

T2

Expected DZ correlation if all influence due to genes

Expected MZ correlation if all influence due to genes

T1

T2

Actual MZ correlation for end of first grade word reading efficiency

T1

T2

International Longitudinal Twin Study of Early Reading, Language, and Attention Development

Brian Byrne, Richard Olson, Stefan Samuelsson

Twins seen in homes or pre-schools at age 4, prior to kindergarten

Twins typically tested at home during summer break after kindergarten

And again during summer break after first grade

With a “final” assessment after second grade

Colorado Sample Characteristics for MZ and Same-Sex DZ Twins

• Representative sample of 489 twin pairs ascertained from birth records, all English first language.

• Most from Colorado Front-Range (Colorado Springs-Denver-Boulder-Fort Collins).

• First tested at preschool age 4-5, followed up at end of kindergarten, 1st, 2nd, while children are “learning to read,” and 4th grade while children are “reading to learn”

Genetic and Environmental Influences on Preschool Print Knowledge in Colorado

(Samuelsson et al., 2007)

Heritability = .26(.13-.41)

Australia = .25,Scandinavia = .20

Shared Environment = .65(.51-.76)

Nonshared Environment = .09(.06-.14)

(95% confidence intervals in parentheses)

Kindergarten TOWRE Word Reading Efficiency in Colorado (Samuelsson et al., 2007)

Heritability = .61(.45, .81)

Australia = .89,Scandinavia = .38

Shared Environment = .33(.12, .49)

Nonshared Environment = .07(.05, .09)

Genetic and Environmental Influences on Individual Differences in Preschool and Kindergarten Reading

• Shared family environment influence is the major influence on preschool print knowledge in all countries

• Genetic influence on reading increases in kindergarten, but varies depending on amount and consistency of kindergarten instruction which is high in Australia (heritability 89%), medium in Colorado (heritability 61%), and low in Scandinavia (heritability 38%)

• The country differences in kindergarten heritability are related to when reading is taught.

End-of-First Grade Word Reading Efficiency in Colorado (Byrne et al., 2007)

Heritability = .79(.55, .92)

Australia = .74,Scandinavia = .78

Shared Environment = .09(.00, .30)

Nonshared Environment = .11(.08, .15)

Conclusions about genetic and environmental influences on the early development of word

reading efficiency in Colorado

• Shared environment influences are dominant for “print knowledge” at preschool age

• Genetic influence begins its dominance for word reading efficiency by the end of kindergarten, but shared environment influence remains significant

• Genetic influence becomes strongly dominant by the end of first grade, as children vary in their responses to formal instruction in their schools (RTI!)

• We see a similar developmental pattern for spelling from kindergarten through first grade

End of Kindergarten Spelling in Colorado (Byrne et al., 2007)

Heritability = .35(.14, .58)

Australia = .72,Scandinavia = .45

Nonshared Environment = .25(.20, .33)

SharedEnvironment = .40(.18, .57)

End of First Grade Spelling in Colorado (Byrne et al., 2007)

Heritability = .65(.36, .82)

Australia = .74,Scandinavia = .85Shared

Environment = .12(.00, .38)

Nonshared Environment = .23(.17, .31)

End of First Grade Woodcock-Johnson III Reading Comprehension in Colorado

(Byrne et al., 2006)

Heritability = .77(.51-.94)

Australia = .77,Ohio, Petrill .76

Shared Environment = .04(.00-.26)

Nonshared Environment = .19(.06-.26)

1st grade Woodcock Reading Comprehension in Australia, Colorado, and Ohio (Petrill)

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Genetic

Shared Env.NonShared E.

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Moderator

Standardized Variance

A^2

C^2

E^2

G x E interaction with parents’ average years of educ.

for individual differences in TOWRE word rec. at the

end of kindergarten in the Colorado sample

genetic

Shared Env.

Non Shared Env.

Low Years of Ed. High

A2, C2 and E2 Estimates as a Function of Parental Ed. In First Grade

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-3.00 -2.50 -2.00 -1.50 -1.00 -0.50 0.00 0.50 1.00 1.50 2.00 2.50 3.00

Moderator

Standardized Variance

A 2̂

C 2̂

E 2̂

Are there different genes influencing different reading skills?

• Genetic correlations are above .9 for word reading, spelling, and reading comprehension at the end of first grade (Byrne et al., 2006)

• However, there is partial independence for genetic influences on word recognition and reading comprehension skills in older children. (Keenan et al., (2006) “Is starting to figure it out”)

Implications for Public Policy on Education

• By the end of first grade, genes account for between 65 and 80 percent of individual differences in word reading, spelling, and reading comprehension in Australia, Colorado, and Scandinavia

• But “No Child Left Behind” makes no mention of genetic influence, and instead blames teachers and schools for children’s reading failure…

• …which may be true in extreme cases, but what is their average influence on individual differences in reading at the end of 1st grade in Colorado?

“Failing” Teacher Influences on Individual Differences in Reading?

• Jonathan Alter (Newsweek, Feb. 12, 2007)“…anyone with an ounce of brains knows what must be done.” “It’s time to move from identifying failing schools to identifying failing teachers.”

• But if teachers are the main influence on individual differences in early reading development, on average, twins sharing the same teacher should be much more similar than twins who have different teachers…

Colorado Correlations for MZ Pairs in Same (N=74) Versus Different (N=108) 1st Grade Classes

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Word Nonword Spelling Comp.

SameDifferent

No significant differences by same – different class

Colorado Correlations for DZ Pairs in Same (N=83) Versus Different (N=132) 1st Grade Classes

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Word Nonword Spelling Comp.

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No significant differences by same – different class

U.K. TOWRE Correlations for MZ and DZ Pairs in Same Versus Different 1st Grade Classes

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MZ TOWRE DZ TOWRE

SameDifferent

# Pairs: 1038, 578 939, 528

(Nicole Harlaar, Personal Communication, 9/10/2006)

Teacher effects on individual differences in reading and spelling at the end of 1st grade

• Very similar correlations for MZ twins sharing or not sharing the same 1st grade teacher suggest minimal average teacher effects on individual differences (of course teachers do teach the kids to read)

• So anyone with an ounce of brains…(Jonathan Alter)

• However, both twins in a pair go to the same school, and maybe that obscures a real teacher effect because bad schools have bad teachers (suggeston from Ed Steinberg, Special Ed. Director, Colorado Department of Education).

• So lets look at mean school performance effects on individual differences in our twins’ reading scores….

A similar conclusion about teacher effects from…

• Mehta, P.D., Foorman, B.R., Branum-Martin, L., & Taylor, P.W. (2005). Literacy as a unidimensional multilevel construct: Validation, sources of influence, and implications in a longitudinal study in grades 1-4. Scientific Studies of Reading, 9, (2), 85-116.

• Now for school effects on individual differences…

The twins’ mean school performance is assessed by the third-grade Colorado Student

Assessment Profile (CSAP), McGraw-Hill

• 32 multiple choice and 8 constructed response items assessing:

• Use of word recognition for comprehension

• Identification of main idea

• Drawing of inferences

• Summarization

Cronbach Alpha = .89

Standard CSAP score means for the schools attended by our twins

Mean = 573Std.Dev. = 26

(Note that the between-school standard dev. of26 is much lessthan the averagewithin-schoolstandard dev.of ~ 70)

School CSAP correlations with 2nd grade reading and language in green, (second order r

in blue, partialed by parent education)

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TOWRE COMP WRATSPELL

PhoAwr Vocab

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Parent education correlations with 2nd grade reading and language, 2nd order r

partialed by school CSAP %PA

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TOWRE COMP WRATSPELL

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School effects on reading at the end of second grade

• Our twins’ reading and spelling correlations with the average 3rd grade school score on the state test are low (.12 - .14) but statistically significant

• But they are not significant and close to 0 after controlling for their parents’ years of education

• Parent education correlations with their twins reading are not moderated by mean school score

• There may be small average school effects in our sample, but we can’t separate them from the effects associated with parent education

Similar conclusions from…

• McCoach, D.B. et al. (2006). Growing readers: A hierarchical linear model of children’s reading growth during the first two years of school. Journal of Educational Psychology, 98, 14-28.

“…between school differences in achievement [kindergarten and first grade in the Early Childhood Longitudinal Study] are largely explained by differences in school clientele [SES], rather than differences in instruction or resource allocation.”

Conclusions continued…

• But, school quality of instruction has been experimentally manipulated with significant effects on school CSAP scores (Pueblo 60, Sadoski & Willson, 2006)

Percent of Pueblo 60 Third Grade “Proficient” CSAP Scores 1998-2005

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1998 1999 2000 2001 2002 2003 2004 2005

% Prof.

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Pueblo 579 (SD57)District? 530 (SD70)

Overlapping 3rd grade CSAP Distributionsfor Pueblo 60 and Comparable District

(573 is the State average for non ESL kids)

Pueblo 60 Decoding Focus Students Mean Pre- and Post-test Percentiles after 60 hours of

intensive additional instruction

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60708090

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Word Recognition Spelling Reading Rate

Pre-testPost-Test

Elimination of CocaCola (Whole Language) from children’s diets (education) results in massive improvements in reading (Adapted from Byrne, 2005).

before after

dyslexics ?

No child left behind: All children must read at “grade level”

Implications for raising literacy in the population as a whole and among children with learning disabilities

• We can certainly raise the average level of literacy in the U.S. by reading more and better text in and out of school.

• We can also improve reading skills among children with dyslexia with more intensive instruction and greater reading practice, but…

Two take-home lessons

• Most cases of dyslexia (and individual differences) that occur within normal educational environments are not the fault of the child, their parents, their teachers, or their schools

• It is unrealistic to expect all children to reach “grade level”, as the “No Child Left Behind” law insists they must, because some children may have strong genetic or other biological constraints on their reading development

From the “No Child Left Behind” reauthorization web site:

HIGHLIGHTS OF BUILDING ON RESULTS:

Every Child Performing at or Above Grade Level by 2014

Accountability—States will be held accountable for ensuring that all students can read and do math at grade level by 2014.

http://www.ed.gov/policy/elsec/leg/nclb/factsheets/blueprint.html

From Robert Linn, co-director,National Center for Research on Evaluation…

UCLA

• “There is a zero percent chance that we will ever reach a 100 percent target….But because the title of the law is so rhetorically brilliant, politicians are afraid to change this completely unrealistic standard. They don’t want to be accused of leaving some children behind.”

(from Washington Post, 3/14/07)

From the U.S. Secretary of Education, Margaret Spellings:

• “In the past, we underestimated what students with disabilities could learn…We now know that the vast majority of these children can achieve grade-level standards.”

• http://www.ed.gov/policy/elsec/leg/nclb/factsheets/blueprint.html

From U.S. Deputy Education Secretary Raymond Simon

• “We need to stay the course…the mission is doable, and we don’t need to back off that right now.”

(Amit R. Paley,Washington Post, 3/14/2007)

From Sen. Lamar Alexander, former U.S. Education Secretary

• “Are we going to rewrite the Declaration of Independence and say only 85% of men are created equal?”

(Amit R. Paley,Washington Post, 3/14/2007)

From Daniel Koretz, Harvard Professor of Education

• Most people are afraid that once you acknowledge this variation [differences among children of the same racial or socioeconomic background], then you have to tolerate major inequities between black and white students.” “That’s not necessarily true, but that’s why the political world does not really address the issue.”

(by Amit R. Paley,Washington Post, 3/14/2007)

• See also, Steve Pinker’s Blank Slate, Ch. 8, fear of inequality