Twin study: Difference between revisions
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Twin studies assume that monozygous and dizygous twins have similar prenatal environments; however, the fetal environments of monozygous and dizygous twins may differ.<ref name="pmid8096890">{{cite journal |author=Phillips DI |title=Twin studies in medical research: can they tell us whether diseases are genetically determined? |journal=Lancet |volume=341 |issue=8851 |pages=1008–9 |year=1993 |pmid=8096890 |doi=}}</ref><ref name="pmid12269999">{{cite journal |author=Sørensen TI |title=Contributions and potentials of Swedish twin research |journal=J. Intern. Med. |volume=252 |issue=3 |pages=181–3 |year=2002 |pmid=12269999 |doi=}}</ref> | Twin studies assume that monozygous and dizygous twins have similar prenatal environments; however, the fetal environments of monozygous and dizygous twins may differ.<ref name="pmid8096890">{{cite journal |author=Phillips DI |title=Twin studies in medical research: can they tell us whether diseases are genetically determined? |journal=Lancet |volume=341 |issue=8851 |pages=1008–9 |year=1993 |pmid=8096890 |doi=}}</ref><ref name="pmid12269999">{{cite journal |author=Sørensen TI |title=Contributions and potentials of Swedish twin research |journal=J. Intern. Med. |volume=252 |issue=3 |pages=181–3 |year=2002 |pmid=12269999 |doi=}}</ref> | ||
As a separate problem, about one third of monozygotic twins are dichorionic. Dichorionic type twins have separate sets of fetal membranes due to their common ovum having divided at an early stage.<ref name="pmid8096890">{{cite journal |author=Phillips DI |title=Twin studies in medical research: can they tell us whether diseases are genetically determined? |journal=Lancet |volume=341 |issue=8851 |pages=1008–9 |year=1993 |pmid=8096890 |doi=}}</ref> The importance of this can be shown in studies that find different rates of concordance between monozygotic twins that are monochorionic verus dichorionic.<ref name="pmid11360946">{{cite journal |author=Loos RJ, Beunen G, Fagard R, Derom C, Vlietinck R, Phillips DI |title=Twin studies and estimates of heritability |journal=Lancet |volume=357 |issue=9266 |pages=1445 |year=2001 |pmid=11360946 |doi=}}</ref> Some experts propose that twin studies should exclude monozygotic monochorionic pairs and monozygous dichorionic pairs with different birthweights.<ref name="pmid8096890">{{cite journal |author=Phillips DI |title=Twin studies in medical research: can they tell us whether diseases are genetically determined? |journal=Lancet |volume=341 |issue=8851 |pages=1008–9 |year=1993 |pmid=8096890 |doi=}}</ref> | As a separate problem, about one third of monozygotic twins are dichorionic. Dichorionic type twins have separate sets of fetal membranes due to their common ovum having divided at an early stage.<ref name="pmid8096890">{{cite journal |author=Phillips DI |title=Twin studies in medical research: can they tell us whether diseases are genetically determined? |journal=Lancet |volume=341 |issue=8851 |pages=1008–9 |year=1993 |pmid=8096890 |doi=}}</ref> The importance of this can be shown in studies that find different rates of concordance between monozygotic twins that are monochorionic verus dichorionic.<ref name="pmid11360946">{{cite journal |author=Loos RJ, Beunen G, Fagard R, Derom C, Vlietinck R, Phillips DI |title=Twin studies and estimates of heritability |journal=Lancet |volume=357 |issue=9266 |pages=1445 |year=2001 |pmid=11360946 |doi=10.1016/S0140-6736(00)04594-3}}</ref> Some experts propose that twin studies should exclude monozygotic monochorionic pairs and monozygous dichorionic pairs with different birthweights.<ref name="pmid8096890">{{cite journal |author=Phillips DI |title=Twin studies in medical research: can they tell us whether diseases are genetically determined? |journal=Lancet |volume=341 |issue=8851 |pages=1008–9 |year=1993 |pmid=8096890 |doi=}}</ref> | ||
===Methods of recruiting twins for study=== | ===Methods of recruiting twins for study=== | ||
Revision as of 22:18, 28 February 2008
Twin studies can help determine the proportion of cases of a disease that are due to inherited versus environmental factors.[1]
Classification
Hawkes proposed the following types of twin studies:[1]
Classical twin method
The classical twin method compares outcome concordance rates in monozygotic and dizygotic twins.
Co-twin control method
In the co-twin control method, discordant monozygotic are closely compared which creates matched pair control. In this design, a single pair of twins may sometimes suffice.
Biometrical genetic methods
Problems with twin studies
Prenatal environment
Twin studies assume that monozygous and dizygous twins have similar prenatal environments; however, the fetal environments of monozygous and dizygous twins may differ.[2][3]
As a separate problem, about one third of monozygotic twins are dichorionic. Dichorionic type twins have separate sets of fetal membranes due to their common ovum having divided at an early stage.[2] The importance of this can be shown in studies that find different rates of concordance between monozygotic twins that are monochorionic verus dichorionic.[4] Some experts propose that twin studies should exclude monozygotic monochorionic pairs and monozygous dichorionic pairs with different birthweights.[2]
Methods of recruiting twins for study
Twins should be recruited from regional and national registries such as the Swedish Twin Registry.[5]. Recruiting volunteer pairs may bias towards monozygotic concordance.[1]
References
- ↑ 1.0 1.1 1.2 Hawkes CH (1997). "Twin studies in medicine--what do they tell us?". QJM 90 (5): 311–21. PMID 9205666. [e]
- ↑ 2.0 2.1 2.2 Phillips DI (1993). "Twin studies in medical research: can they tell us whether diseases are genetically determined?". Lancet 341 (8851): 1008–9. PMID 8096890. [e]
- ↑ Sørensen TI (2002). "Contributions and potentials of Swedish twin research". J. Intern. Med. 252 (3): 181–3. PMID 12269999. [e]
- ↑ Loos RJ, Beunen G, Fagard R, Derom C, Vlietinck R, Phillips DI (2001). "Twin studies and estimates of heritability". Lancet 357 (9266): 1445. DOI:10.1016/S0140-6736(00)04594-3. PMID 11360946. Research Blogging.
- ↑ Lichtenstein P, De Faire U, Floderus B, Svartengren M, Svedberg P, Pedersen NL (2002). "The Swedish Twin Registry: a unique resource for clinical, epidemiological and genetic studies". J. Intern. Med. 252 (3): 184–205. PMID 12270000. [e]