I have just documented the origins, methods, findings, implications and controversies of this study in a book titled, BORN TOGETHER-REARED APART: THE LANDMARK MINNESOTA TWIN STUDY (Harvard University Press, 2012). The book includes marvelous pictures of some of the twins we studied, as well as the amazing life history events responsible for their separation and eventual reunion.
The reared apart twin design provides one of the best approaches to studying genetic and environmental influence on behaviors involves the rare pairs of identical and fraternal twins reared apart and reunited. The size of the correlation between reared apart identical co-twins offer scientists a pure estimate of genetic influence on behavioral and physical traits. The size of the correlation between reared apart fraternal co-twins provides an informative comparison. Greater resemblance between identical than fraternal twins is consistent with genetic influence on the traits under study.
The Minnesota study began in 1979 and continued for twenty years. The volume of material that accumulated was too vast to include in a single volume. I have, therefore, included some supplementary material in a web site: drnancysegaltwins.org. Information about my other books can also be found there.
It is amazing that twins continue to be separated today, given the increased appreciation for family ties. In the past, twins were separated mostly due to illegitimacy or maternal death. Today, the new assisted reproductive technologies that may yield several babies, not just one, have caused some families to relinquish one or more of their multiple birth children; these families may lack the resources to properly care for them. China’s One-Child Policy was also indirectly responsible for the separation of pairs of mostly female twins. In fact, I am studying those twins, as well. And new cases occasionally cross my desk from unexpected sources. These cases are all scientifically informative in their own way, but bringing the twins together is the most satisfying part of the process.
1. Francis G. Inquiries into Human Faculty and its Development. London: Macmilan & Co; 1875. History of Twins; pp. 155–73.
2. Guo SW. Does higher concordance in monozygotic twins than in dizygotic twins suggest a genetic component? Hum Hered. 2001;51:121–32.[PubMed]
3. Palmer B. Double inanity twin studies are pretty much useless. [Last accessed on 2014 Jun 3]. Available from: http://www.slate.com/authors.brian_palmer.html .
4. Liew SH, Elsner H, Spector TD, Hammond CJ. The first “classical” twin study? Analysis of refractive error using monozygotic and dizygotic twins published in 1922. Twin Res Hum Genet. 2005;8:198–200.[PubMed]
5. Holden C. Identical twins reared apart. Science. 1980;207:1323.[PubMed]
6. Katherine Neer. How Twins Work. [Last accessed on 2014 Jun 3]. Available from: http://science.how stuffworks.com/life/genetic/twin.html .
7. Bouchard TJ, Jr, Lykken DT, McGue M, Segal NL, Tellegen A. Sources of human psychological differences: The Minnesota Study of twins reared apart. Science. 1990;250:223–8.[PubMed]
8. Genetics and Social sciences. Twin studies. [Last accessed on 2014 Jun 3]. Available from: http://www.nchpeg.org/bssr/index.php .
9. Norwegian Institute of Public Health. Norwegian twin registry. [Last accessed on 2014 Jun 3]. Available from: http://www.fhi.no/eway/default.aspx?pid=240&trg=MainContent_6898&Main_6664=6898:0:25,7697:1:0:0:::0:0&MainContent_6898=6706:0:25,8379:1:0:0:::0:0 .
10. Nilsen TS, Knudsen GP, Gervin K, Brandt I, Røysamb E, Tambs K, et al. The Norwegian twin registry from a public health perspective: A research update. Twin Res Hum Genet. 2013;16:285–95.[PubMed]
11. Hopper JL, Foley DL, White PA, Pollaers V. Australian twin registry: 30 years of progress. Twin Res Hum Genet. 2013;16:34–42.[PubMed]
12. Sumathipala A, Siribaddana S, Hotopf M, McGuffin P, Glozier N, Ball H, et al. The Sri Lankan twin registry: 2012 update. Twin Res Hum Genet. 2013;16:307–12.[PubMed]
13. Skytthe A, Kyvik K, Bathum L, Holm N, Vaupel JW, Christensen K. The Danish twin registry in the new millennium. Twin Res Hum Genet. 2006;9:763–71.[PubMed]
14. University of Southern Denmark. The Danish twin registry. [Last accessed on 2014 Jun 3]. Available from: http://www.sdu.dk/en/omsdu/instituttercentre/ist_sundhedstjenesteforsk/centre/dtr .
15. Lichtenstein P, De Faire U, Floderus B, Svartengren M, Svedberg P, Pedersen NL. The Swedish twin registry: A unique resource for clinical, epidemiological and genetic studies. J Intern Med. 2002;252:184–205.[PubMed]
16. Karolinska Institute. Swedish Twin Registry. [Last accessed on 2014 Jun 3]. Available from: http://ki.se/en/research/the-swedish-twin-registry-1 .
17. University of Minnesota. Minnesota centre for twins and family research. [Last accessed on 2014 Jun 3]. Available from: https: //mctfr.psych.umn.edu/aboutus/index.html .
18. Institute for research and development. Twin registry. [Last accessed on 2014 Jun 3]. Available from: http://www.ird.lk /Twin%20Registry.php .
19. Ravindran V, Rajendran S, Elias G. Primary antiphospholipid syndrome in monozygotic twins. Lupus. 2013;22:92–4.[PubMed]
20. Rao RM, Reddy GP, Grim CE. Relative role of genes and environment on BP: Twin studies in Madras, India. J Hum Hypertens. 1993;7:451–5.[PubMed]
21. Allison DB, Faith MS, Nathan JS. Risch's lambda values for human obesity. Int J Obes Relat Metab Disord. 1996;20:990–9.[PubMed]
22. Patel AB, Renge RL. Tetralogy of Fallot in monozygotic twins. Indian Heart J. 2002;54:83–5.[PubMed]
23. Chatterjee S, Das N. Lung function in Indian twin children: Comparison of genetic versus environmental influence. Ann Hum Biol. 1995;22:289–303.[PubMed]
24. Kriplani A, Banerjee N, Takkar D. Etiology and management of monoamniotic twin discordant for anencephaly. Acta Genet Med Gemellol (Roma) 1998;47:51–5.[PubMed]
25. Sharma K. Genetic epidemiology of epilepsy: A twin study. Neurol India. 2005;53:93–8.[PubMed]
26. Jain S, Jain MS, Padma MV, Puri A, Sen P, Maheshwari MC. Epilepsies among twins born in families of Indian probands with epilepsy. Seizure. 1998;7:139–43.[PubMed]
27. Gupta P, Faridi MM, Batra M. Physiological skin manifestations in twins: Association with maternal and neonatal factors. Pediatr Dermatol. 2011;28:387–92.[PubMed]
28. Sharma K, Bakshi S. Genetic analysis of bilateral dermatoglyphic asymmetry in twins and their parents. Anthropol Anz. 2005;63:165–87.[PubMed]
29. Dirani M, Islam A, Shekar SN, Baird PN. Dominant genetic effects on corneal astigmatism: The genes in Myopia (GEM) twin study. Invest Ophthalmol Vis Sci. 2008;49:1339–43.[PubMed]
30. Azad R, Chandra P, Patwardhan SD, Gupta A. Profile of asymmetrical retinopathy of prematurity in twins. Indian J Ophthalmol. 2010;58:209–11.[PMC free article][PubMed]
31. Srivastava S, Khalid A, Lal N. Mania in twins: A case report. Indian J Psychiat. 1996;38:260–2.[PMC free article][PubMed]
32. Yadav SK, Kumari A, Javed S, Ali S. DYZ1 arrays show sequence variation between the monozygotic males. BMC Genet. 2014;15:19.[PMC free article][PubMed]
33. Jena AK, Duggal R, Mathur VP, Parkash H. Class-III malocclusion: Genetics or environment? A twins study. J Indian Soc Pedod Prev Dent. 2005;23:27–30.[PubMed]
34. Gupta M, Divyashree R, Abhilash P, A Bijle MN, Murali K. Correlation between Chronological Age, dental age and skeletal age among monozygoyic and dizygotic twins. J Int Oral Health. 2013;5:16–22.[PMC free article][PubMed]
35. Sreedevi G, Srinivas B, Reddy TP, Prasad CM, Kumar BS, Satish R. Heritability of thirty cephalometric parameters on monozygotic and dizygotic twins: Twin study method. J Contemp Dent Pract. 2013;14:304–11.[PubMed]
36. Lovelina FD, Shastri SM, Kumar PD. Assessment of the oral health status of monozygotic and dizygotic twins - a comparative study. Oral Health Prev Dent. 2012;10:135–9.[PubMed]
37. Katsika D, Grjibovski A, Einarsson C, Lammert F, Lichtenstein P, Marschall HU. Genetic and environmental influences on symptomatic gallstone disease: A Swedish study of 43,141 twin pairs. Hepatology. 2005;41:1138–43.[PubMed]
38. Carlin JB, Gurrin LC, Sterne JA, Morley R, Dwyer T. Regression models for twin studies: A critical review. Int J Epidemiol. 2005;34:1089–99.[PubMed]
39. Katsika D, Tuvblad C, Einarsson C, Lichtenstein P, Marschall HU. Body mass index, alcohol, tobacco and symptomatic gallstone disease: A Swedish twin study. J Intern Med. 2007;262:581–7.[PubMed]