Mosaicism for deletion 17p11.2 in a boy with the Smith-Magenis syndrome.

We describe a 14-year-old boy with physical and behavioral manifestations of the Smith-Magenis syndrome. Low level mosaicism (11%) for deletion 17p11.2 was found in peripheral blood lymphocytes. The deletion was also observed in 100% of metaphases examined from skin fibroblast cultures. We confirm that the Smith-Magenis syndrome is associated with a highly recognizable phenotype. Because evidence of the abnormal cell line may be minimal or absent in peripheral blood, fibroblast studies are indicated for patients in whom mosaicism for deletion 17p11.2 is suspected clinically.