Molecular diagnosis of 22q11.2 deletion and duplication by multiplex ligation dependent probe amplification

22q11 Deletion syndrome (22q11DS) is the most common microdeletion syndrome in humans, occurring with an incidence of I in 4,000. In most cases the submicroscopic deletion spans 3 Mb, but there are a number of other overlapping and non-overlapping deletions that generate a similar phenotype. The majority of the 22q11.2 microdeletions can be ascertained using a standard fluorescence in situ hybridization (FISH) assay probing for TUPLE I or N25 on 22q11.2. However, this test fails to detect deletions that are either proximal or distal to the FISH probes, and does not provide any information about the length of the deletion. In order to increase the detection rate of 22q11.2 deletion and to better characterize the size and position of such deletions we undertook a study of 22q11.2 cases using multiplex ligation dependent probe amplification (MLPA). We used MLPA to estimate the size of the 22q11.2 deletions in 51 patients positive for TUPLE1 or N25 (FISH) testing, and to investigate 12 patients with clinical features suggestive of 22q11DS and negative FISH results. MLPA analysis confirmed a microdeletion in all 51 FISH-positive samples as well as microduplications in three samples. Further, it allowed us to delineate deletions not previously detected using standard clinical FISH probes in 2 of 12 subjects with clinical features Suggestive of 22q11DS. We conclude that MLPA is a costeffective and accurate diagnostic tool for 22q11DS with a higher sensitivity than FISH alone. Additional advantages of MLPA testing in our study included determination of deletion length and detection of 22q11.2 duplications. (C) 2007 Wiley-Liss, Inc.