The Kleberg Cytogenetics Laboratory offers fluorescence in situ hybridization (FISH)-based assays for identifying the deletions of 22q associated with DiGeorge syndrome, velocardiofacial syndrome (VCFS), Shprintzen syndrome and isolated conotruncal cardiac defects, and deletions on 10p associated with the DiGeorge Syndrome II locus. The laboratory tests for both critical regions (10p13p14 and 22q11.2) using a dual-probe FISH assay.

Clinical Features:

The phenotypic features of DiGeorge syndrome consist of thymic aplasia or hypoplasia, hypocalcemia and conotruncal cardiac defects. Many patients die of cardiac complications or infections due to poor immunity. Velocardiofacial (Shprintzen) syndrome often presents with overt or submucous cleft palate, conotruncal defects, hypotonia, dysmorphic facies, developmental delay, small stature and velopharyngeal incompetence. Because of significant overlap of both syndromes, some clinicians refer to this syndrome as 22q11 deletion syndrome. There is significant inter- and intrafamilial clinical variability due to deletion of 22q11. A second deletion of 10p13p14 (DiGeorge Syndrome II) has been associated with similar clinical features.

Reasons for Referral:

Patients with clinical features suggestive of DiGeorge syndrome or VCFS may be tested for deletions of 10p13p14 and 22q11.2 simultaneously. If a deletion of 22q has already been ruled out and DiGeorge syndrome is still suspected, testing for the 10p deletion only may be ordered. FISH analysis is indicated on the parents of an affected child since approximately 6% of affected probands will have inherited the deletion from a parent. Prenatal diagnosis may be performed if an affected family member has been studied in our laboratory and shown to have a deletion detectable by FISH. In addition, prenatal diagnosis may be indicated in patients with ultrasound anomalies of the heart, specifically conotruncal defects. Please call regarding all prenatal samples.

Testing Methodology:

FISH is the application of fluorescently labeled DNA molecules to metaphase chromosomes and interphase nuclei for the detection of chromosome abnormalities and alterations. It is a rapid, reliable and direct approach for identifying patients with microdeletions or microduplications. This dual-probe FISH assay can detect deletions on chromosome 22q11.2 and chromosome 10p13p14. FISH analysis for DiGeorge/VCFS is performed on metaphase chromosomes. The absence of a hybridization signal indicates a deletion. Of patients fitting the clinical description, approximately 95% will demonstrate a deletion of 22q11. The deletion of 10p13p14 is rare and is usually detected by a high-resolution karyotype. The remaining patients may have a deletion undetectable by current commercially available probes.

Specimen Requirements:

Whole blood in sodium heparin (green-top) tubes:
Newborn (< 3 months): Minimum 0.5 -2.0 CC
Adult/Child: Minimum 3.0 -5.0 CC

Shipping and Handling:

All tubes must be labeled with the patient's testname and date of birth, and a completed requisition form must accompany each sample. If the laboratory is billing the patient's insurance, please enclose a copy of the insurance card. Ship specimens for overnight delivery at ambient temperature. Please notify the laboratory of incoming samples.

Turnaround Time: