1. Why are the causal effects of shared environment so small?
Paul Lichtenstein, professor
Head of department
Department of Medical Epidemiology and Biostatistics Karolinska Institutet, Sweden

2. Outline The question: Why do we care about shared environment
The method: Twin and family methods
The empirical results: Very little shared environment for psychiatric phenotypes
The meaning: How should we interpret the limited effect of the shared environment?
The conclusion: Life is unfair – should we bother?

3. Familial aggregation WHY?? Genes? Environments?
Lichtenstein et al, 2009, Lancet

4. Nature or Nuture? Environ-ments Genes 1920 1800 1960 1950 1980 1970
Mendel’s inheritance laws rediscovered
1960
1950
DNA discovered
1980
1970
Reaction to Nazism
2000
Development of molecular genetics
Left- and environmental concentration on public debate
Human genome project
After Plomin & Petrill, Intelligence, 1997

5. The twin method: Correlations

6. The twin method: Correlations

7. The twin method: Correlations

8. The twin method: Correlations

9. The Twin method: Model fitting
MZ = 1.0
DZ = 0.5 1 E A C C A E e a c c a e T1 T2

10. Sweden best in class Swedish Twin Register
The Multi-Generation Register

11. The Multi-Generation Registry
Individuals born in Sweden > 1932
N ~ 9 million
Link with biological and adoptive parents
N ~ 15 million

12. Pedigrees from the MGR Full cousins Half cousins Half siblings
II:1
II:2
II:3
II:4
II:5
II:6
II:7
III:1
III:2
III:3
III:4
III:5
III:6
III:7
III:8
Full cousins
Half cousins
Half siblings
Full siblings

13. Extended children-of-twins model (ECOT)

14. Percentage of Variance Personality: Meta analyses of twin and adoption studies
Familial aggregation most often due to genetic factors
Environmental effects most often unique for each family member
Shared environment (family environment) small (but significant) effect
After Loehlin,1992

15. MaTCH MaTCH http://match.ctglab.nl
Contains summary results from 2,748 twin studies
527 studies of the eight PGC disorders

16. MaTCH – 8 PGC disorders N studies N MZ pairs N DZ pairs
N studies
N MZ pairs
N DZ pairs
Alcohol Dependence
153
94,477
94,196
Anorexia Nervosa 50
18,917
6,458
ADHD 89
86,450
121,139
Autism Spectrum Disorder 26
37,329
68,559
Bipolar Disorder 10
9,251
15,752
Major Depressive Disorder
163
98,314
121,935
Obsessive Compulsive Disorder 24
25,806
31,994
Schizophrenia 12
19,841
29,457

17. Shared environment - no or small effect
Abnormal environment?
What phenotype?
What is shared environment – really?
How much could you expect?
Why are people so provoked?

18. Abnormal environment
Severe deprivation during early childhood influence development!
Rutter and Romanian adoptees (summarized in JAACAP, 2012)
Severe deprivation
Quasi-autism
Disinhibited attachment
Inattention/overactivity
Cognitive impairment

19. Romanian children adopted to British families before and after age 6 months
Rutter et al, JAACAP , 2012

20. What phenotype?
Some phenotypes do show clear shared environmental effects
Externalizing behavior
Criminality
Substance abuse
Socioeconomic status

21. Frisell et al, Psychol Med , 2011

22. Percentage of Variance Convictions for violent criminality
Frisell et al, Psychol Med , 2011

23. Abuse Twin, sibling and adoption studies (Kendler and Sundqvists)
Kendler et al, Psychol Med , 2016

24. Andel av variationen Utbildningsnivå i födelsekohorter
Män
*Lichtenstein, Pedersen & McClearn, 1992, Acta Sociologica
**Fischbein, Lange & Lichtenstein, 1997, Scandinavian Journal of Educational Research

25. Andel av variationen Utbildningsnivå i födelsekohorter
Män
Kvinnor?
*Lichtenstein, Pedersen & McClearn, 1992, Acta Sociologica
**Fischbein, Lange & Lichtenstein, 1997, Scandinavian Journal of Educational Research

26. Andel av variationen Utbildningsnivå i födelsekohorter
Män
Kvinnor
*Lichtenstein, Pedersen & McClearn, 1992, Acta Sociologica
**Fischbein, Lange & Lichtenstein, 1997, Scandinavian Journal of Educational Research

27. What is (shared) environment?

28. Percentage of Variance Stressful life events
We (our genes) influence our environment
The more controllable – the higher heritability
Plomin et al, 1990, Psychol Aging

29. Neighborhood deprivation ”is genetic”
Sariaslan et al, Transl Psychiatry , 2016

30. How about parenting? Parental criticism: Girls 16 year old
The child’s genes influence ”parenting”
Evocative gene-environment correlation
Narusyte et al, 2007, Europ Child & Adol Psychiatry

31. Shared environment - no or small effect
Abnormal environment?
What phenotype?
What is shared environment – really?
How much could you expect?
Why are people so provoked?

32. Shared environment - no or small effect
Abnormal environment?
What phenotype?
What is shared environment – really?
How much could you expect?
Why are people so provoked?

33. Conclusion
Shared environment have limited effects – especially for severe psychopathology
Does not mean that parenting and treatment are meaningless
No causal effects of shared environment but causal effects of parenting
Life is unfair – would it be better if it was because of the shared environment?