Duplication/deletion mosaicism of the 7q(21.1 --> 31.3) region.

Mosaicism for structural aberrations is a rare event and the coexistence of a cell line with a duplication and another with a deletion of the same chromosome segment is even more infrequent. We report a boy with a 46,XY,del(7q)/46,XY,dup(7q) mosaicism. High-resolution cytogenetic analysis and fluorescent in situ hybridization (FISH) performed at birth showed a trisomy for region 7q21.1 to 7q31.3 in 90% of metaphases analyzed and monosomy for the same region in 10% of metaphases. At the age of 12 months, karyotype on peripheral blood and exfoliated urinary epithelial cells was 46,XY,dup(7)(q21.1q31.3) in all cells analyzed. The patient presented malformations and psychomotor retardation. His phenotype is compared with other previously case reports describing patients with an interstitial duplication of 7(q21 or q22 --> q31.3). Due to the absence of a normal cell line, we propose a post-zygotic origin of the abnormality during the first mitotic division and a progressive loss of the deleted cells during pre- and post-natal development by selective pressure. The patient described here emphasizes the possible existence of an undetectable cell line in patients previously diagnosed of pure partial 7q trisomy or monosomy to explain the great clinical variability between reported patients. We also describe the culture of urinary epithelial cells in order to perform cytogenetic analysis as a useful non-invasive method.