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

Abstract

The 22q11 deletion syndrome , which is caused by a 1.5-to 3.0-megabase hemizygous deletion in chromosome 22q11.2 , has a prevalence of 1/2000 to 1/4000. However , the syndrome presents with highly variable phenotypes and thus may be underestimated among Danish newborns. To establish a true incidence of 22q11.2 deletions among certain manifestations, eg, congenital heart disease , on selected Danes , a multiplex ligation-dependant probe amplification (MLPA) analysis was designed. The analysis was planned to be performed on DNA extracted from dried blood spot samples (DBSS) obtained from Guthrie cards collected during neonatal screening programs. However, the DNA concentration necessary for a standard MLPA analysis (20 ng) could not be attained from DBSS, and a novel MLPA design was developed to permit for analysis on limited amounts of DNA (2 ng). A pilot study is reported here that validates the new MLPA design using nine patients diagnosed with the 22q11.2 deletion and 101 controls. All deletions were identified using DNA extracted from DBSS , and no copy number variations were detected in the controls , resulting in a specificity and sensitivity of 100%. It is thereby concluded that the novel MLPA probe design is successful and reliable using minimal amounts of DNA. This allows for use of DBSS samples in a retrospective study of 22q11.2 deletion among certain manifestations associated with

Discussing the psychiatric manifestations of 22q11.2 deletion syndrome: an exploration of clinical practice among medical geneticists

“…This represents an important area for future research, especially given the current discussion regarding whether 22q11DS is a condition that should potentially be included in newborn screening panels. 18,32 If 22q11DS is included in newborn screening, diagnoses will increasingly be made at earlier ages. Because followup visits may not be occurring as often as intended, it will be important to identify strategies to facilitate return visits for patients and their families.…”

22q11.2 deletion syndrome

“…2). Thus, nested deletions excluding the LCR22A–LCR22B region (that is, LCR22B–LCR22D and LCR22C–LCR22D deletions) can be detected using customized FISH probes from the LCR22B–LCR22D region or more easily using clinically available whole-region methodologies, such as multiplex ligation-dependent probe amplification 194,195 or single-nucleotide polymorphism microarrays. As genome-wide microarrays detect pathogenic copy number variants on all chromosomes, this methodology has the added benefit of not introducing bias by requiring pre-selection of a specific genomic region.…”

The benefits and limitations of cell‐free DNA screening for 22q11.2 deletion syndrome

“…Historically, fluorescence in situ hybridization (FISH) has been the most frequent diagnostic test used to identify a 22q11.2 deletion, using a probe mapping within the LCR22A to LCR22B region . (Figure ) Nested deletions excluding the LCR22A–B region, for example, LCR22B–D and LCR22C–D deletions, can only be detected using whole genome copy number variant approaches such as comparative genomic hybridization (CGH), multiplex ligation‐dependent probe amplification (MLPA), or single nucleotide polymorphism (SNP) microarrays; thus, these smaller deletions would be missed by FISH studies alone . When an amniocentesis is performed following a cell‐free DNA screening that is positive for the 22q11.2 deletion or based on ultrasound findings such as congenital heart defects, the primary diagnostic study should be a microarray.…”