DiGeorge/VCFS/22q11 Microdeletion
Test Overview
CPT Code(s)
Peripheral Blood: 88230-52, 88271, 88273, 88291
Amniotic Fluid: 88235-52, 88271, 88273, 88291
Methodology
Culture/Hybridization/Microscopy/Interpretation
Specimen Requirements
| Type | Peripheral Blood | Amniotic Fluid |
|---|---|---|
| Container | Sodium Heparin (green top tube) | Two 15 ml sterile leak-proof conical tubes |
| Optimal Quantity | 2-3 ml | 20-25 ml |
| Minimum Quantity | 1-2 ml | 10 ml |
| Storage | Room Temperature | Room Temperature |
| Stability at Room Temperature | Room Temperature for 8 hours, then refrigerate | Room Temperature for 8 hours, then refrigerate |
| Transportation | Avoid freezing or heating over 35oC | Avoid freezing or heating over 35oC |
The 22q11 microdeletion is associated with DiGeorge or velocardiofacial (VCFS) syndrome which is an autosomal dominant condition with variable expressivity resulting in variable phenotype. Patients with this deletion show characteristic features such as craniofacial anomalies, mental retardation, and congenital heart defect. Among the heart defects, tetralogy of Fallot is the most common. Several studies have recommended that any child with a congenital heart defect should be tested for 22q11 microdeletion since this deletion is very common in about 20% of patients with syndromic heart defects. The 22q11 microdeletion is also referred to as CATCH22 for cardiac defects, abnormal facies, thymic hypoplasia, cleft palate and hypocalcemia. Since the most common deletion encompasses ~3 Mb, often these deletions are not detected on routine chromosome analysis. FISH is the ideal choice for detection of this deletion due to its increased sensitivity.
Methods
The sample is usually cultured until sufficient number of mitotic cells is observed (48-72 hours for peripheral blood and 7-10 days for amniotic fluid) and after harvesting the cells are hybridized with the probes. After hybridization and post-hybridization washes, the slides are analyzed under a fluorescence microscope equipped with epifluorescence and appropriate filter sets. Analysis and scoring is carried out by two certified technologists in a blinded fashion with each scoring a minimum of 5 metaphases and 50 interphase nuclei. Results are reviewed by both the laboratory manager and the director.
22q11 deletion (DiGeorge / VCFS syndrome) HIRA / TUPLE1 Cytocell (cat #LPU004)
Interpretation of Results
The morphologic interpretation and correlation of results on all cases is performed by a board-certified doctoral level scientist (laboratory director). The final report has a narrative description of results. If abnormalities are present, they are explained in a paragraph which helps to clarify and correlate chromosomal findings with phenotype. References are included in the report to help the referring physician with interpretation, which include books or journals that contain appropriate information. Recommendations are made as to any additional testing, if necessary.