Whether monozygotic (MZ) and dizygotic (DZ) twins differ from each other in a variety of phenotypes is important for genetic twin modeling and for inferences made from twin studies in general. We analyzed whether there were differences in individual, maternal and paternal education between MZ and DZ twins in a large pooled dataset. Information was gathered on individual education for 218,362 adult twins from 27 twin cohorts (53% females; 39% MZ twins), and on maternal and paternal education for 147,315 and 143,056 twins respectively, from 28 twin cohorts (52% females; 38% MZ twins). Together, we had information on individual or parental education from 42 twin cohorts representing 19 countries. The original education classifications were transformed to education years and analyzed using linear regression models. Overall, MZ males had 0.26 (95% CI [0.21, 0.31]) years and MZ females 0.17 (95% CI [0.12, 0.21]) years longer education than DZ twins. The zygosity difference became smaller in more recent birth cohorts for both males and females. Parental education was somewhat longer for fathers of DZ twins in cohorts born in 1990-1999 (0.16 years, 95% CI [0.08, 0.25]) and 2000 or later (0.11 years, 95% CI [0.00, 0.22]), compared with fathers of MZ twins. The results show that the years of both individual and parental education are largely similar in MZ and DZ twins. We suggest that the socio-economic differences between MZ and DZ twins are so small that inferences based upon genetic modeling of twin data are not affected.
Silventoinen K, Jelenkovic A, Latvala A, Sund R, Yokoyama Y, Ullemar V, Almqvist C, Derom CA, Vlietinck RF, Loos RJF, Kandler C, Honda C, Inui F, Iwatani Y, Watanabe M, Rebato E, Stazi MA, Fagnani C, Brescianini S, Hur YM, Jeong HU, Cutler TL, Hopper JL, Busjahn A, Saudino KJ, Ji F, Ning F, Pang Z, Rose RJ, Koskenvuo M, Heikkilä K, Cozen W, Hwang AE, Mack TM, Siribaddana SH, Hotopf M, Sumathipala A, Rijsdijk F, Sung J, Kim J, Lee J, Lee S, Nelson TL, Whitfield KE, Tan Q, Zhang D, Llewellyn CH, Fisher A, Burt SA, Klump KL, Knafo-Noam A, Mankuta D, Abramson L, Medland SE, Martin NG, Montgomery GW, Magnusson PKE, Pedersen NL, Dahl Aslan AK, Corley RP, Huibregtse BM, Öncel SY, Aliev F, Krueger RF, McGue M, Pahlen S, Willemsen G, Bartels M, van Beijsterveldt CEM, Silberg JL, Eaves LJ, Maes HH, Harris JR, Brandt I, Nilsen TS, Rasmussen F, Tynelius P, Baker LA, Tuvblad C, Ordoñana JR, Sánchez-Romera JF, Colodro-Conde L, Gatz M, Butler DA, Lichtenstein P, Goldberg JH, Harden KP, Tucker-Drob EM, Duncan GE, Buchwald D, Tarnoki AD, Tarnoki DL, Franz CE, Kremen WS, Lyons MJ, Maia JA, Freitas DL, Turkheimer E, Sørensen TIA, Boomsma DI, Kaprio J. Education in Twins and Their Parents Across Birth Cohorts Over 100 years: An Individual-Level Pooled Analysis of 42-Twin Cohorts. Twin Res Hum Genet. 2017 Oct;20(5):395-405. PMC5969906.