22q11 Deletion syndrome (22q11DS) is the most common microdeletion syndrome in 
humans, occurring with an incidence of 1 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 TUPLE1 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 cost-effective 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.