Education in Twins and Their Parents Across Birth Cohorts Over 100 years: An Individual-Level Pooled Analysis of 42-Twin Cohorts
Authors: Silventoinen Karri , Jelenkovic Aline , Latvala Antti , Sund Reijo , Yokoyama Yoshie , Ullemar Vilhelmina , Almqvist Catarina , Derom Catherine A. , Vlietinck Robert F. , Loos Ruth J. F. , Kandler Christian , Honda Chika , Inui Fujio , Iwatani Yoshinori , Watanabe Mikio , Rebato Esther , Stazi Maria A. , Fagnani Corrado , Brescianini Sonia , Hur Yoon-Mi , Jeong Hoe-Uk , Cutler Tessa L. , Hopper John L. , Busjahn Andreas , Saudino Kimberly J. , Ji Fuling , Ning Feng , Pang Zengchang , Rose Richard J. , Koskenvuo Markku , Heikkilä Kauko , Cozen Wendy , Hwang Amie E. , Mack Thomas M. , Siribaddana Sisira H. , Hotopf Matthew , Sumathipala Athula , Rijsdijk Fruhling , Sung Joohon , Kim Jina , Lee Jooyeon , Lee Sooji , Nelson Tracy L. , Whitfield Keith E. , Tan Qihua , Zhang Dongfeng , Llewellyn Clare H. , Fisher Abigail , Burt S. Alexandra , Klump Kelly L. , Knafo-Noam Ariel , Mankuta David , Abramson Lior , Medland Sarah E. , Martin Nicholas G. , Montgomery Grant W. , Magnusson Patrik K. E. , Pedersen Nancy L. , Dahl Aslan Anna K. , Corley Robin P. , Huibregtse Brooke M. , Öncel Sevgi Y. , Aliev Fazil , Krueger Robert F. , McGue Matt , Pahlen Shandell , Willemsen Gonneke , Bartels Meike , van Beijsterveldt Catharina E. M. , Silberg Judy L. , Eaves Lindon J. , Maes Hermine H. , Harris Jennifer R. , Brandt Ingunn , Nilsen Thomas S. , Rasmussen Finn , Tynelius Per , Baker Laura A. , Tuvblad Catherine , Ordoñana Juan R. , Sánchez-Romera Juan F. , Colodro-Conde Lucia , Gatz Margaret , Butler David A. , Lichtenstein Paul , Goldberg Jack H. , Harden K. Paige , Tucker-Drob Elliot M. , Duncan Glen E. , Buchwald Dedra , Tarnoki Adam D. , Tarnoki David L. , Franz Carol E. , Kremen William S. , Lyons Michael J. , Maia José A. , Freitas Duarte L. , Turkheimer Eric , Sørensen Thorkild I. A. , Boomsma Dorret I. , Kaprio Jaakko 
Published: October 2017

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.