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. The overall birth prevalence of 22q11.2 deletions appears to be approximately 1 in 4,000, with 75% of these patients having cardiac abnormalities, which represents the major cause of mortality in 22q11.2 DS. Developmental delay, facial dysmorphia, palatal dysfunction, and feeding difficulties are also seen in most infants 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) (https://www.ncbi.nlm.nih.gov/books/NBK1523/
22q11.2 Duplication Syndrome is a condition caused by an extra copy of a piece of chromosome 22 (~3Mb). 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 weak muscle tone (hypotonia). Many patients with the condition have no apparent physical or intellectual disabilities. The 22q11.2 Duplication Syndrome is about half as common as 22q11.2 DS (Draaken et al. 2010, Sedghi et al. 2015).
Cat Eye Syndrome (CES) has a large phenotypic variability, ranging from near normal to severe malformations. The eyes are predominately affected. CES is caused by the presence of an extra 22q11.2 copy between the DGS region and centromere, and usually present as a small extra chromosome, frequently having two centromeres (https://www.omim.org/entry/115470
). In many cases this chromosomal abnormality is mosaic.
The high frequency of 22q11.2 copy number changes is due to the presence of several copies of a repeat sequence (LCR22). The extent of the 22q11.2 deletions is variable, although the majority (~90%) extend from the first (LCR22-A) until the fourth (LCR22-D) repeat. In this P250 DiGeorge probemix, 14 probes are located in this repeat region, see Table 2. In 8% of the cases, the deletion extends from only LCR22-A to LCR22-B (Michaelovsky et al. 2012). In 2% of the cases, the deletion extends from LCR22-A to LCR22-C or the deletion starts from a site between LCR22-A and LCR22-B and extends to LCR22-D. This deletion includes TBX1
genes (Du et al. 2020). Haploinsufficiency of the TBX1
gene in particular is responsible for most of the physical malformations. Point mutations in this gene have also been observed in individuals with DGS. Although the majority of DGS cases appear to be due to a 22q11.2 deletion, chromosome defects on 4q, 8p, 9q, 10p, 17p with features of DiGeorge anomaly have also been described (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 and can be used to distinguish the most common types of deletion; 4 of the 29 probes targeting 22q11.2 and 1 probe targeting 22q11.1 region are in the Cat Eye Syndrome region. 17 Probes are present for regions relevant for DGS type II or disorders with phenotypic features of DGS on chromosomes 4q, 8p, 9q, 10p, 17p. Furthermore, 2 probes for 22q13 are present (Table 1 and Table 2). These 19 probes are also used as reference probes for sample normalisation. Complete probe sequences and the identity of the genes detected by the reference probes 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