FISH investigation of 22q11.2 deletion in patients with immunodeficiency and/or cardiac abnormalities. 
DiGeorge anomaly/velocardiofacial syndrome (DG/VCFS), called 22q11.2 deletion syndrome in general, is the most common chromosomal deletion syndrome found in humans.  Typical facial features, palatal defects, conotruncal abnormalities of the heart, aplasia/hypoplasia of the parathyroid glands and of thymus are characteristics of this syndrome.  Deletions of chromosome 22q11.2 (del22q11.2) are the leading causes of DG7VCFS.  We report on a systematic search by fluorescence in situ hybridization (FISH) for deletions of chromosomes 22q11.2 in patients with a clinical suspicion or diagnosis of DG/VCFS.  Using FISH we studied a series of 43 patients with suspected DG/VCFS.  In this study, a total of 43 patients were investigated for the presence of a 22q11.2 deletion over a two-year period.  Del22q11.2 was detected in 5 of the 43 patients tested.  All patients with deletion had hypocalcemia, 80% had cardiac defects, 40% had facial dysmorphism, 40% had immunodeficiency , and 20% had otolaryngeal abnormalities.  Chromosome 22q11.2 deletion is a relatively common condition and is readily diagnosed by FISH.  We suggest that FISH analysis of 22q11.2 deletion should be performed in the presence of combined of hypocalcemia and congenital cardiac malformations, with or without any characteristics of the disease.  This may facilitate an early diagnosis in such patients.