Relationship between the IQ of people with Prader–Willi syndrome and that of their siblings: evidence for imprinted gene effects
Article first published online: 4 FEB 2009
© 2009 The Authors. Journal Compilation © 2009 Blackwell Publishing Ltd
Journal of Intellectual Disability Research
Volume 53, Issue 5, pages 411–418, May 2009
How to Cite
Whittington, J., Holland, A. and Webb, T. (2009), Relationship between the IQ of people with Prader–Willi syndrome and that of their siblings: evidence for imprinted gene effects. Journal of Intellectual Disability Research, 53: 411–418. doi: 10.1111/j.1365-2788.2009.01157.x
- Issue published online: 14 APR 2009
- Article first published online: 4 FEB 2009
- Accepted 13 January 2009
- Prader-Willi syndrome;
- genetic subtypes;
- sibling IQ
Background Genetic disorders occasionally provide the means to uncover potential mechanisms linking gene expression and physical or cognitive characteristics or behaviour. Prader–Willi syndrome (PWS) is one such genetic disorder in which differences between the two main genetic subtypes have been documented (e.g. higher verbal IQ in one vs. higher performance IQ in the other; slower than normal reaction time in one vs. normal in the other). In a population study of PWS, the IQ distribution of people with PWS was approximately normal. This raises the question of whether this distribution arose from a systematic effect of PWS on IQ (hypothesis 1) or whether it was the fortuitous result of random effects (hypothesis 2).
Method The correlation between PWS and sibling IQ was determined in order to discriminate between the two hypotheses. In the first case we would expect the correlation to be similar to that found in the general population (0.5); in the second case it would be zero.
Results It was found that the overall PWS–sibling IQ correlation was 0.3 but that the two main genetic subtypes of PWS differed in their familial IQ relationships. As expected, the IQs of normal siblings correlated 0.5, and this was also the case with one genetic subtype of PWS (uniparental disomy) and their siblings, while the other subtype IQ correlated −0.07 with sibling IQ.
Conclusions This is a potentially powerful result that gives another clue to the role of genes on chromosome 15 in the determination of IQ. It is another systematic difference between the genetic subtypes of PWS, which needs an explanation in terms of the very small genetic differences between them.