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LETTERS: D I Boomsma, C E M van Beijsterveldt, M J H Rietveld, M Bartels, and G C M van Baal Genetics mediate relation of birth weight to childhood IQ BMJ 2001; 323: 1426a [Full text]

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Different Explanation of the Dizygotic and Monozygotic Twin Pairs Data

Clayman ZK Zhang   (26 April 2002)

Different Explanation of the Dizygotic and Monozygotic Twin Pairs Data 26 April 2002
Clayman ZK Zhang, Research Staff MRC Environmental Epidemiology Unit,Southampton,SO16 6YD Send response to journal: Re: Different Explanation of the Dizygotic and Monozygotic Twin Pairs Data	Sir- Professor Boomsma's letter(BMJ 2001;323:1426) offered a valueble oppoturenaty to give a detailed examination of the relative role of genetic and environmental factors in determining IQ. We can easily found that the association between birth weight and IQ disappeared as we inspect the table attached in the letter by the way as Pro. Boomsma inspected it. It also seems giving us a hint that IQ is mainly determinded by environmental factors,because as age advanced,the IQ between lowest and highest birth weight approached each other in both typesof twin pairs. But when you examine the data in some detail,you can also easily find two interesting results:(1)that those with highest birth weight tends to have higher IQ score in both groups regardless weather ajusting the gestational age or not,and (2)that those with highest birth weight certainly have higher IQ score before 7 years old in both type of twin pairs. This means that the association between birth weight and IQ realy exist in young children and the association can also be confounded by rearing environment.