Using MZ Differences in the Search for Nonshared Environmental Effects

Abstract

Behavioural genetic research has shown that environmental influences relevant to the development of individual differences are largely nonshared in origin. That is, environmental influences do not make children in the same family similar to one another, however, little is known about which specific aspects of the environment are responsible. Identical (MZ) twins provide a uniquely powerful tool to search for specific nonshared environmental influences independent of nonshared genetics because such twins do not differ genetically. The sample consisted of 93 MZ twin pairs aged 10-18 years from the Nonshared Environment and Adolescent Development (NEAD) project. Reports of parental negativity and adolescent adjustment were obtained from parents, ratings of videotaped observations, and the adolescents themselves. Relative differences of mothers' and fathers' negativity within MZ pairs correlated significantly with MZ differences in antisocial behaviour. The correlations were moderate for within-reporter associations, but were negligible for associations between reporters. Possible interpretations for these source-specific findings are discussed.

Why are Children in the Same Family So Different? Nonshared Environment a Decade Later

“…Hardly any non shared en vi ron mental me di ating ef fects re mained in de pend ent of ge netic me dia tion. The find ing that non shared en vi ron ment fails to me di ate these asso cia tions is sup ported by sim pler analy ses that found lit tle as so cia tion be tween iden ti cal twin dif fer ences in fam ily en viron ment and iden ti cal twin dif fer ences in ado les cent outcomes-an ana lytic ap proach that di rectly as sesses non shared en vi ron mental me dia tion of the as so cia tion (48). The find ing of ge netic me dia tion im plies that, to a sub stan tial ex tent, dif fer en tial pa ren tal treat ment of sib lings re flects geneti cally in flu enced dif fer ences be tween the sib lings.…”

A Discordant Monozygotic-Twin Approach to Potential Risk Factors for Chronic Widespread Pain in Females

“…The design allows to test whether environmental factors (such as psychosocial factors in relation to CWP) are responsible for the presence of the condition in one twin compared to the co-twin who does not have the condition. As these factors are often assumed to be part of the 'NSE' component of variation often found in classical twin studies, this technique provides some indications as to which NSE factors are actually important (Dick et al, 2000;Jinks & Fulker, 1970;Kaprio et al, 1993;Pike et al, 1996). This approach overcomes many of the traditional limitations associated with conventional epidemiology because trait-discordant MZ twins are completely matched for genetics, age, sex, cohort effects, maternal influences, common environmental factors (those shared by siblings), and are closely matched for other environmental factors (such as early upbringing and lifestyle; (Dick et al, 2000;Jinks & Fulker, 1970;Kaprio et al, 1993)).…”

Nonshared Environmental Influences on Sleep Quality: A Study of Monozygotic Twin Differences

“…The MZ twin differences design has been used to determine specific nonshared environmental effects for a number of traits, for example behavioural development and adolescent depression (Asbury et al 2003;Caspi et al 2004;Liang and Eley 2005), and is a simple yet powerful method of determining twin discrepancy that is independent of genetics and the shared environment (Pike et al 1996).…”