FISH Diagnosis of 22q11.2 Deletion Syndrome

The 22q11.2 deletion syndrome is the most common microdeletion syndrome. Although once thought to be separate disorders, cardiac anomalies, abnormal face, thymic hypoplasia, cleft palate, hypocalcemia, and chromosome 22 deletions (CATCH 22); DiGeorge syndrome; velocardiofacial syndrome; and conotruncal anomaly face syndrome are now known to be part of the same 22q11.2 deletion syndrome. Diagnosis of this syndrome is extremely challenging because of wide variability in phenotypic presentations. When the deletion is suspected, genetic testing is typically ordered. Conventional karyotyping is only capable of detecting a small percentage of chromosome deletions. However, fluorescence in situ hybridization (FISH) is capable of detecting many deletions and microdeletions. This article discusses the pathophysiology and presentation of chromosome 22q11.2 deletion syndrome. The use of FISH as a diagnostic tool is also described, including the FISH process, its use, and its accuracy and reliability in the diagnosis of chromosome 22q11.2 deletion syndrome in the fetus and/or newborn.