Relationship between the IQ of people with Prader-Willi syndrome and that of their siblings: evidence for imprinted gene effects.
Prader-Willi deletion breaks the usual sibling IQ link, while disomy keeps it, hinting that imprinted genes drive cognitive differences.
01Research in Context
What this study did
The team looked at brothers and sisters of people with Prader-Willi syndrome.
They asked: do the IQ scores of siblings still match the usual 0.5 link when one child has PWS?
They split the PWS group by genetic subtype: deletion or uniparental disomy.
What they found
In families where the child had the deletion subtype, the normal sibling IQ link vanished.
In families with the disomy subtype, the sibling IQ link stayed near 0.5, just like typical kids.
The break in the deletion families points to imprinted genes shaping thinking skills.
How this fits with other research
Bruns et al. (2004) first mapped lower IQ and different skill profiles for each subtype.
Poppes et al. (2010) later showed the same pattern holds in adults, giving the idea a longer shelf life.
Together the three papers build a chain: subtype shapes cognition, and now we see it even alters family IQ patterns.
Why it matters
When you assess a client with PWS, note the genetic report. Deletion cases may have extra cognitive risk that brothers and sisters do not share. Disomy cases follow more typical family ability levels. Use this to set realistic skill targets and to guide parents about sibling expectations.
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02At a glance
03Original abstract
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.
Journal of intellectual disability research : JIDR, 2009 · doi:10.1111/j.1365-2788.2009.01157.x