The SALSA MLPA Probemix P250 DiGeorge is an in vitro diagnostic (IVD)1
or a research use only (RUO) semi-quantitative assay2
for the detection of deletions or duplications in the human 22q11.2 region in genomic DNA isolated from human peripheral whole blood specimens, buccal swabs, (un)cultured amniotic fluid obtained in week 16 of the pregnancy or later and free from blood contamination, (un)cultured chorionic villi free from maternal contamination, or fetal blood. P250 DiGeorge is intended to confirm a potential cause for and clinical diagnosis of 22q11.2 Deletion/Duplication Syndrome or Cat Eye Syndrome (CES). It further contains probes for the detection of copy number status on 4q, 8p, 9q, 10p, and 17p regions to confirm a potential cause for and clinical diagnosis of DiGeorge (DGS) type II or disorders with phenotypic features of DGS. This assay is suitable for initial detection of deletions or duplications of above-mentioned regions or for confirmation of results obtained with a different (MLPA) assay.
Copy number variations (CNVs) detected with P250 DiGeorge should be confirmed with a different technique. In particular, CNVs detected by only a single probe always require confirmation by another method.
Assay results are intended to be used in conjunction with other clinical and diagnostic findings, consistent with professional standards of practice, including confirmation by alternative methods, parental evaluation, clinical genetic evaluation, and counselling, as appropriate. The results of this test should be interpreted by a clinical molecular geneticist or equivalent.
This device is not intended to be used for standalone diagnostic purposes, population screening, or for the detection of, or screening for, acquired or somatic genetic aberrations.
Please note that this probemix is for In Vitro Diagnostic use (IVD) in the countries specified at the end of this product description. In all other countries, the product is for Research Use Only (RUO).
To be used in combination with a SALSA MLPA Reagent Kit and Coffalyser.Net analysis software.
One of the most common genetic disorders causing learning disabilities and mild mental retardation is 22q11.2 Deletion Syndrome (DS). 22q11.2 DS is an autosomal dominant contiguous gene deletion syndrome with a live birth prevalence estimated between 1:3,000 and 1:6,000 among the general population. Cardiac abnormalities are present in ~75% of 22q11.2 DS patients and are the major cause of mortality. Developmental delay, facial dysmorphia, palatal dysfunction, and feeding difficulties are also observed in most individuals with this syndrome. It is now recognized that 22q11.2 DS encompasses the phenotypes previously described as DiGeorge syndrome (DGS), velocardiofacial syndrome (VCFS), conotruncal anomaly face syndrome (CTAF), and Cayler cardiofacial syndrome (asymmetric crying facies), (GeneReview: https://www.ncbi.nlm.nih.gov/books/NBK1523/
22q11.2 Duplication syndrome (DupS) is a condition caused by an extra copy of a part of chromosome 22 (~3 Mb). The features of this condition vary widely, even among members of the same family (intrafamilial variability). Affected individuals may have intellectual or learning disability, developmental delay, slow growth leading to short stature, and hypotonia. Many individuals with a 22q11.2 duplication have no apparent physical or intellectual phenotype (Draaken et al. 2010, Sedghi et al. 2015). 22q11.2 DupS is much rarer than 22q11.2 DS, and its prevalence remains undetermined.
Cat Eye Syndrome (CES) has a large phenotypic variability, ranging from near normal to severe physical malformations, predominately affecting the eyes. CES is caused by the presence of an extra 22q11.2 copy between the DGS region and centromere, which usually presents as a small extra chromosome, frequently having two centromeres (https://www.omim.org/entry/115470
). In many cases this chromosomal abnormality is mosaic.
The relatively high frequency of 22q11.2 copy number changes is prompted by low-copy number repeat (LCR22) sequences situated in this region. The span of the 22q11.2 deletions is variable, although the most common one (~85%) extends from the first (LCR22-A) until the fourth (LCR22-D) repeat (Table 2), leading to the typical 2.54 Mb deletion. In this P250 DiGeorge probemix, 14 probes target this repeat region. Two other deletions, the proximal nested 1.5-Mb (LCR22A-LCR22B) and 2-Mb (LCR22A-LCR22C) have a combined relative frequency of 5-10%. The distal nested (LCR22B-LCR22D and LCR22C-LCR22D) and other more distal deletions flanked by LCRs C-E; D-E; D-F; E-F; F-G are rare, and combined they only explain about 2% of cases (Lima et al. 2010; Michaelovsky et al. 2012; McDonald-McGinn et al. 2015). Haploinsufficiency of the TBX1
gene, situated between LCR22A and -B, is particularly responsible for most of the physical phenotype observed in 22q11.2 DS. Point mutations in TBX1
have also been observed in individuals with DGS-like phenotypes. Although the majority of DGS cases are explained by 22q11.2 deletions, chromosome defects on 4q, 8p, 9q, 10p, and 17p have also been associated with DiGeorge-like symptoms (see Table 2 for more information).
The SALSA MLPA Probemix P250 DiGeorge contains 48 MLPA probes with amplification products between 129 and 487 nucleotides (nt): 29 probes are located in the 22q11.2 region; four of the 29 probes for 22q11.2 and one probe for 22q11.1 target the Cat Eye Syndrome region. In addition, 17 probes are present for regions relevant for DGS type II or disorders with phenotypic features similar to DGS, and target chromosomal regions 4q, 8p, 9q, 10p, 17p. Two probes are included that target 22q13 (Table 1 and 2). These 19 probes also serve as reference probes. Complete probe sequences are available online (www.mrcholland.com
This probemix contains nine quality control fragments generating amplification products between 64 and 105 nt: four DNA Quantity fragments (Q-fragments), two DNA Denaturation fragments (D-fragments), one Benchmark fragment, and one chromosome X and one chromosome Y-specific fragment. More information on how to interpret observations on these control fragments can be found in the MLPA General Protocol and online at www.mrcholland.com