Hostname: page-component-848d4c4894-pjpqr Total loading time: 0 Render date: 2024-06-29T13:36:31.941Z Has data issue: false hasContentIssue false
  • English
  • Français

The “Equal Environments Assumption” in MZ-DZ Twin Comparisons: an Untenable Premise of Psychiatric Genetics?

Published online by Cambridge University Press:  01 August 2014

A. Pam ,
S.S. Kemker ,
C.A. Ross  and
R. Golden
A. Pam*
Affiliation:
Albert Einstein College of Medicine, Bronx, New York
S.S. Kemker
Affiliation:
Albert Einstein College of Medicine, Bronx, New York
C.A. Ross
Affiliation:
Dissociative Disorders Unit, Charter Hospital of Dallas Richardson, Texas, USA
R. Golden
Affiliation:
Albert Einstein College of Medicine, Bronx, New York
*
Director of Psychology, Bronx Psychiatric Center, 1500 Waters Place, Bronx, New York 10461, USA

Abstract

Core share and HTML view are not available for this content. However, as you have access to this content, a full PDF is available via the ‘Save PDF’ action button.

The comparison of MZ-DZ twins in behavioral genetics has produced what seems like irrefutable evidence for the heritability of many psychiatric disorders. But such research depends on the validity of the EEA – the “equal environments assumption” – as an underlying premise. In this paper, several empirical studies which support the EEA are critically reviewed in terms of methodology and the way data has been processed in a mathematical model called “path analysis”. It turns out that studies investigating the EEA appear to be largely inadequate in terms of technique, as well as biased in the inferences drawn. Further, the “heritability” estimate – often taken to mean the influence of trait – specific genes – is merely a statistical abstraction derived from a matrix of correlations; this estimate encompasses many buried environmental effects so that “heritability” does not correspond to any underlying DNA structure. In conclusion, many MZ-DZ pedigree studies have dubious scientific value, given the non-viable premise of the EEA, as well as the misleading operational definition of what has been called “heritability”.

Type
Research Article
Information
Acta geneticae medicae et gemellologiae: twin research , Volume 45 , Issue 3 , July 1996 , pp. 349 - 360
Copyright
Copyright © The International Society for Twin Studies 1996

References

REFERENCES

1.Ainslie, RC, Olmstead, KM, O'Laughlin, DD (1987): The early developmental context of twinship: some limitations of the equal environments assumption. Am J Orthopsychiatry, 57: 120–124.Google Scholar
2.Boring, EG (1923): Intelligence as the tests test it. New Republic, 35: 35–37Google Scholar
3.Carey, G, Di Lalla, DL (1994): Personality and psychopathology: genetic perspectives. J Abn Psychol, 103: 32–43.CrossRefGoogle ScholarPubMed
4.Carson, RC, Sanislow, CA (1993): The schizophrenias, in Comprehensive Handbook of Psychopathology. Edited by Sutker, PB & Adams, HE, second etidion.CrossRefGoogle Scholar
5.Cassou, B, Schiff, M, Stewart, J (1980): Génétique et schizophrénie: réévaluation d'un consensus. Psychiatrie de l'Enfant, 23: 87–201.Google Scholar
6.Cloninger, CR, Rao, DC, Rice, J, Reich, T, Norton, NE (1983): A defense of path analysis in genetic epidemiology. Am J Hum Gen, 35: 733–756.Google Scholar
7.Craike, W, Slater, E (1945): Folie a deux in uniovular twins reared apart. Brain, 68: 213–221.CrossRefGoogle ScholarPubMed
8.Eaves, LJ, Eysenck, HJ, Martin, NG: Genes, Culture, and Personality: An Empirical Approach. London: Academic Press, 1989.Google Scholar
9.Ford, BD (1193): Emergenesis: an alternative and a confound. Am Psychol, 48: 1294.Google Scholar
10.Gottesman, II, Shields, J: Schizophrenia – The Epigenetic Puzzle. Cambridge, Cambridge University Press, 1982.Google Scholar
11.Jackson, D (1960): A critique of the literature on the genetics of schizophrenia, in The Etiology of Schizophrenia. Edited by Jackson, D. New York, Basic Books.CrossRefGoogle Scholar
12.Kamin, L: The Science and Politics of IQ. Potomac, Maryland, Ehrlbaum, 1974.Google Scholar
13.Karlin, S, Cameron, EC, Chakraborty, R (1983): Path analysis in genetic epidemiology: a critique. Am J Hum Genet 35: 695–732.Google Scholar
14.Kendler, KS (1986): Genetics of schizophrenia. Psychiatric Update 5: 25–41.Google Scholar
15.Kendler, KS (1993): Twin studies of psychiatric illness. Arch Gen Psychiatry 50: 905–915.Google Scholar
16.Kendler, KS, Neale, MC, Kessler, RC, Heath, AC, Eaves, LJ (1993): A test of the equal-environment assumption in twin studies of psychiatric illness. Behav Genet 23: 21–27.Google Scholar
17.Kety, S (1979): Disorders of the human brain. Sci Am 241: 202–214.Google Scholar
18.Konner, M: The Tangled Wing: Biological Constraints on the Human Spirit. New York, Holt, Rinchart & Winston, 1982.Google Scholar
19.Lewontin, R, Rose, S, Kamin, L: Not in our Genes: Biology, Ideology, and Human Nature. New York, Pantheon, 1984.Google Scholar
20.Lytton, H (1977): Do parents create, or respond to, differences in twins? Dev Psychol 13: 456–459.Google Scholar
21.Matheny, AP, Wilson, RS, Dolan, AB (1976): Relations between twins' similarity of appearance and behavioral similarity: testing an assumption. Behav Genet 6: 343–351.Google Scholar
22.Morris-Yates, A, Andrews, G, Howie, P, & Henderson, S (1990): Twins: a test of the equal environments assumption. Acta Psychiatr Scand 81: 322–326.CrossRefGoogle ScholarPubMed
23.Plomin, R, Willerman, L, Loehlin, JC (1976): Resemblance in appearance and the equal environments assumption in twin studies of personality traits. Behav Genet 6: 43–52.CrossRefGoogle ScholarPubMed
24.Plomin, R, Defries, JC, McClearn, GK: Behavior Genetics: A Primer. San Francisco, WH Freeman, 1980.Google Scholar
25.Rowe, DC (1981): Environmental and genetic influences on dimensions of perceived parenting: a twin study. Dev Psychol 17: 203–208.Google Scholar
26.Rowe, DC (1983): A biometrical analysis of perceptions of family environment: a study of twins and singleton sibling kinships. Child Dev 54: 416–423.Google Scholar
27.Sacks, O: The man who mistook his wife for a hat and other clinical tales. London, Duckworth; 1985.Google Scholar
28.Scarr, S, Carter-Saltzman, L (1979): Twin method: defense of a critical assumption. Behav Genet 9: 527–542.Google Scholar
29.Torrey, ER, Bowler, EA, Taylor, EH, Gottesman, II: The Biological Roots of Mental Illness as Revealed by the Landmark Study of Identical Twins. New York, Basic Books, 1994.Google Scholar
30.Vandenberg, SG (1984): Does a special twin situation contribute to similarity for abilities in MZ and DZ twins? Acta Genet Med Gemellol 33: 219–222.Google Scholar
31.Wallace, M: The Silent Twins. New York, Ballantine, 1986.Google Scholar
32.Wright, S (1983): On “Path analysis in genetic epidemiology: a critique”. Am J Hum Genet 35: 757–768.Google Scholar
33.Zerbin-Rudin, E (1972): Genetic research and the theory of schizophrenia. Int J Ment Health 1: 42–62.CrossRefGoogle Scholar