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Comparison of academic performance of twins and singletons in adolescence: follow-up study

BMJ 2006; 333 doi: https://doi.org/10.1136/bmj.38959.650903.7C (Published 23 November 2006) Cite this as: BMJ 2006;333:1095

Genetic contributions to intelligence differ between monozygotic and dizygotic twin pairs

Dear Editor,

In the article by Christensen et al. titled 'Comparison of academic
performance of twins and singletons in adolescence: follow-up study' the
authors report that twins show similar academic performance in adolescence
to singletons, and birth weight showed little to no affect on academic
performance (1). In support of previous comments, this study however has
failed to identify (include) the more important intelligence differences
which have recently been identified between monozygotic and dizygotic twin
pairs (2,3).

1. Christensen K, Petersen I, Skytthe A, Herskind AM, McGue M,
Bingley P. Comparison of academic performance of twins and singletons in
adolescence: follow-up study.
BMJ. 2006: 333(7578):1095.

2. Hulshoff Pol HE, Schnack HG, Posthuma D, Mandl RC, Baare WF, van
Oel C, van Haren NE, Collins DL, Evans AC, Amunts K, Burgel U, Zilles K,
de Geus E, Boomsma DI, Kahn RS. Genetic contributions to human brain
morphology and intelligence.
J Neurosci. 2006: 26(40):10235-42.

3. Potter GG, Plassman BL, Helms MJ, Foster SM, Edwards NW.
Occupational characteristics and cognitive performance among elderly male
twins. Neurology. 2006: 67(8):1377-82.

Competing interests:
None declared

Competing interests: No competing interests

30 November 2006
Kenneth A Hoekstra, PhD
Assistant Professor of Pathology
Portland, Oregon 97230