More than 70 different mutations have been identified and many are missense or protein truncating types which mainly involve C→T transitions. Even though a mutation in theMECP2 gene has still not been found in ∼20-25% of girls with classical Rett syndrome, large deletions or intragenic inversions would not be detectable by the methodology used. Some limited FISH and Southern blotting studies aimed at detecting such large mutations have so far not done so.34 The very large 3′UTR has also not been studied