Dual-probe fluorescence in situ hybridization assay for detecting deletions associated with VCFS/DiGeorge syndrome I and DiGeorge syndrome II loci

Abstract

Over 90% of patients with DiGeorge syndrome (DGS) or velocardiofacial syndrome (VCFS) have a microdeletion at 22q11.2. Given that these deletions are difficult to visualize at the light microscopic level, fluorescence in situ hybridization (FISH) has been instrumental in the diagnosis of this disorder. Deletions on the short arm of chromosome 10 are also associated with a DGS-like phenotype. Since deletions at 22q11.2 and at 10p13p14 result in similar findings, we have developed a dual-probe FISH assay for screening samples referred for DGS or VCFS in the clinical laboratory. This assay includes two test probes for the loci, DGSI at 22q11.2 and DGSII at 10p13p14, and centromeric probes for chromosomes 10 and 22. Of 412 patients tested, 54 were found to be deleted for the DGSI locus on chromosome 22 (13%), and a single patient was found deleted for the DGSII locus on chromosome 10 (0. 24%). The patient with the 10p deletion had facial features consistent with VCFS, plus sensorineural hearing loss, and renal anomalies. Cytogenetic analysis showed a large deletion of 10p [46, XX,del(10)(p12.2p14)] and FISH using a 10p telomere region-specific probe confirmed the interstitial nature of the deletion. Analysis for the DGSI and the DGSII loci suggests that the deletion of the DGSII locus on chromosome 10 may be 50 times less frequent than the deletion of DGSI on chromosome 22. The incidence of deletions at 22q11.2 has been estimated to be 1 in 4000 newborns; therefore, the deletion at 10p13p14 may be estimated to occur in 1 in 200,000 live births.

Digeorge syndrome/chromosome 22q11.2 deletion syndrome

“…If the 22q11.2 deletion is not found, the 10p deletion should be sought. One available method detects both deletions simultaneously [49]. It is also common to evaluate chromosomes using standard banding techniques to define large deletions or translocations.…”

BAC array CGH in patients with Velocardiofacial syndrome-like features reveals genomic aberrations on chromosome region 1q21.1

“…Other unrelated chromosomal abnormalities have been reported in 2-4% of patients with suspect of VCFS, including microscopic inversions and interchromosomal imbalances, derivatives of parental translocations, marker chromosomes, apparently balanced translocations, ring chromosomes and sex chromosomes aneuploidies [12-15]. Deletions involving contiguous genes on chromosome 10p have also been reported in some patients with VCFS features [16-18], while mutations in gene T-box 1 ( TBX1 ) account only for a few of reported cases [19,20]. …”

A Girl with Pervasive Developmental Disorder and Complex Chromosome Rearrangement Involving 8p and 10p

“…Microdeletions of two Velocardiofacial syndrome (VCFS) associated loci at 22q.11.2 [TUPLE1, Vysis] and 10p13p14 [SD10p1] (Berend et al, 2000) were excluded by FISH. FISH of SD10p1 done by Kleberg Cytogenetics Laboratory, Baylor College of Medicine showed the presence of the probe in normal chromosome 10p and derivative 8p, indicating no deletion of this probe and confirming the translocation of the segment 10pter-p12.32 onto the der(8) (Fig.…”

“…The critical region is thought to be at 10p13p14 (Berend et al, 2000;Daw et al, 1996;Lipson et al, 1996) this region corresponds to palatal abnormalities, cardiac defects and characteristic faces, as well as renal anomalies and hearing deficits (Gottlieb et al, 1998;Schuffenhauer et al, 1998;Van Esch et al, 1999). Using molecular deletion analysis, Lichtner et al (2000) demonstrated that hemizygosity of the region designated DGCR2 in the proximal 10p region could cause cardiac defects and T cell abnormalities.…”