Prader-Willi Syndrome-Reply FREE

In Reply.—The comments of Drs Wu and Hasen concerning our recent article¹ are appreciated. Three things mentioned by them deserve further comment. First, we of course concur that not all persons clinically thought to have Prader-Willi syndrome have demonstrable deletions of chromosome 15. While this could reflect true causal heterogeneity, we suspect that in many instances lack of rigorous clinical diagnostic criteria may be equally important in explaining this apparent heterogeneity. Second, those instances in which there is no cytogenetically detectable deletion may mean that less than (rather than more than) a simple absence of q11-q12 is sometimes sufficient. This hypothesis—that submicroscopic deletions or even point mutations within this region may sometimes yield the same phenotype—will probably eventually be proved or disproved using DNA probe technology (in conjunction with more rigorous clinical assessment, as already alluded to). Finally, we certainly agree that more needs to be learned about possible