Progress in the autosomal segmental aneusomy syndromes (SASs): single or multi-locus disorders?

Based on cytogenetic observations, several syndromes have been previouslyidentified as microdeletion-based disorders. In this review, recentprogress is presented regarding whether one or multiple genes can beimplicated in the pathogenesis of these segmentally aneusomic syndromes.The syndromes discussed include Angelman, Alagille, Williams,Langer-Giedeon, Prader-Willi, Smith-Magenis, Miller-Dieker, andDiGeorge/velocardiofacial or the 22q11 deletion syndromes. For Angelman andAlagille syndromes, single genes have been identified, whereas for Williamsand Langer-Giedion syndromes, more than one gene can be implicated.Although there has been significant progress in dissecting the molecularbasis for the other disorders, the ultimate answer regarding one versusseveral genes remains to be determined.