MeCP2 Duplication: Rare or Common?

14 June 2009 – Edmonton, AB, Canada From a parent’s perspective one of the strange things about MeCP2 Duplication syndrome is that it has been described both as rare and common. How rare is it?

The answer is really unclear at this point. It is rare, in the sense that the number of diagnosed cases is still quite small. As of one point in 2008, the number of diagnosed cases was counted as 44. Since then, there have been a lot more added, and everyone seems to have lost count but the number is probably still in the low hundreds. The trick is here is that this is the number of DIAGNOSED cases. Diagnosis depends on testing and testing is rare. So the number appears to depend more on the number of tests than on the number of positive tests.

There are several clues hat the actual number might be much higher. These clues come primarily from the percentage of positive tests made among males with severe intellectual disabilities and the percentages of positives among males with X-Linked intellectual disabilities. Based on these, it is possible to make rough estimates. These these suggest that when more information is available, we may be able to make a reasonable estimate of something like 1 out of 50,000 or 75,000 boys have MePC2 Duplication. Please remember at this point this number could be much higher or much lower once there is enough data to make a more precise estimate. If these numbers do hold up, MeCP2 will still be a rare disorder, but a much more common”rare” disorder than it is now.

It could turn out to be about as common as Rett syndrome but it seems virtually impossible  that will turn out to be as common as Fragile-X syndrome.


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