RESUMEN
Williams syndrome (WS) is a well-known genetic disorder caused by heterozygous microdeletions of the 7q11.23 chromosome region. The main clinical features of the syndrome are characteristic facial dysmorphisms, cardiovascular and endocrine anomalies, short stature, mild-to-moderate intellectual disability, and a recognizable cognitive and behavioral profile. Differently from large chromosomal imbalances and aneuploidies, mosaicism has only rarely been found in microdeletion syndromes, and mosaic cases with WS phenotype have never been reported. We here describe a 51-year-old female patient with the typical clinical features of WS, whose chromosomal microarray analysis and fluorescence in situ hybridization disclosed a 54%-68% germline mosaicism for 7q11.23 deletion.