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

Abstract

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.

Case Report Molecular characterization of microduplication 22q11.2 in a girl with hypernasal speech

“…Microduplication 22q11.2 may be largely undetected as a result of a nonspecific/mild phenotype and could be present more frequently in persons without clinical symptoms having a normal to even high intelligence (Courtens et al, 2008). Because it is undetectable by routine G-banded karyotyping, most individuals with 22q11.2 duplication are identified either by array-CGH testing, interphase FISH or multiplex ligation-dependent probe amplification testing for the 22q11.2 deletion syndrome (Stachon et al, 2007). Resolution of just a few hundred base pairs and even down to the single base pair level, as contrasted to conventional cytogenetic analyses with a resolution not better than several tens of thousands of base pairs, now allows high-resolution analyses of cryptic rearrangements (Grigorenko et al, 2010).…”

Detecting 22q11.2 Deletions by Use of Multiplex Ligation-Dependent Probe Amplification on DNA from Neonatal Dried Blood Spot Samples

“…5,6 Since 2002 it has been possible to detect copy number variations by multiplex ligation-dependent probe amplification (MLPA), and this method has been shown to be superior to fluorescence in situ hybridization (FISH). 7,8 The clinical diagnostic consequence of this was demonstrated by Stachon et al 9 who retested a group of 62 patients suspected of 22q11 DS. MLPA confirmed 22q11.2 deletions among 51 patients with positive FISH tests, and detected 2 deletions among the 11 patients with FISH negative results.…”

Caracterização fenotípica em indivíduos com microarranjos na região cromossômica 22q11

“…Três classes de deleções foram identificadas: 3 Mb em 90% dos indivíduos com síndrome VCF, conhecida como a região tipicamente deletada (typically deleted region, TDR); 1,5 Mb em 7% a 8% dos indivíduos, identificada como região crítica DiGeorge (DGRC); rearranjos menores dentro da região crítica de 3 Mb, presentes em 2 a 3% dos casos (AUGUSSEAU et al, 1986;LINDSAY et al, 1995;CARLSON et al, 1997;EDELMANN et al, 1999;REISH et al, 2003;RUITER et al, 2003;D'ANTONI et al, 2004;SHAIKH et al, 2007;STACHON et al, 2007;BASHIR et al, 2008;BLENNOW et al, 2008;EMANUEL, 2008;ROSA et al, 2009;DRAAKEN et al, 2010). …”

“…A SD22q11 se caracteriza por um espectro fenotípico bastante amplo, com efeitos pleiotrópicos que resultam no acometimento de praticamente todos os órgãos e/ou sistemas, altamente variável com mais de 180 sinais clínicos descritos, tanto físicos como comportamentais (Anexo A) (CUNEO, 2001;HAY, 2007;STACHON et al, 2007;ROSA et al, 2009). …”

“…Distinta de outras síndromes de microdeleção cromossômica, em que aspectos do fenótipo parecem estar relacionados com o tamanho da deleção, na SD22q11 a maioria dos estudos não mostra correlação entre o tamanho da deleção e a gravidade do fenótipo (BERTI et al, 2001;STACHON et al, 2007;MAYNARD et al, 2008;SIMIONI, 2008;ROSA et al, 2009;VITHEESAMRANTHAM;SNABBOON, 2014).…”