The article deals with phenotypic signs and molecular cytogenetic diagnostics of chromosomal microdeletion 22q11. This aberration is associated with inborn cardiac defects (especially conotruncal heart anomalies), thymic hypoplasia or aplasia, immunity defects, hypoparathyroidism, neonatal hypocalcaemia, cleft palate and some other dysmorphic features (e.g. low set dysplastic ears, hypertelorism, small mandible, arachnodactyly). This report is based on molecular cytogenetic analysis of 124 patients (mostly newborns or very young children with inborn cardiac defects). In 33 of them (i.e. 27%) microdeletion 22q11 was detected. These results prove an extensive phenotypic variability in all patients with 22q11 microdeletion. Authors present a patient with microdeletion 22q11 with isolated pseudohypoparathyroidism and without other typical features. Phenotypic expressivity varies also in two described familiar cases of microdeletion 22q11 - in mother and daughter of in a mother and her monozygotic twins.

        Key words: CATCH 22, DiGeorge syndrome, chromosome 22, microdeletion 22q11, inborn cardiac defects, tetralogy of Fallot, interrupted aortic arch, immunodeficiency, hypoparathyroidism