A child with complementary mosaic trisomy 8 and mosaic trisomy 21; clinical description of Warkany-Down syndrome and mechanism of origin.

Aneuploidy mosaicism involving two complementary different autosomal trisomy cell lines is extremely rare. Although a mosaic double trisomy 8/trisomy 21 has been described in literature, this is the first report of Warkany (+8)-Down (+21) syndrome due to two complementary mosaic trisomy cell lines. The phenotype of the male patient with Warkany-Down syndrome includes upslanting palpebral fissures, hypertelorism, small low-set ears with unilateral aural stenosis, large and broad hands and feet with deep palmar and plantar creases, bilateral cryptorchidism, generalized mild hypotonia and transient neonatal thrombocytopenia. At the age of two years, his developmental quotient is around 50. His height, weight and head circumference are below the third centile. We speculate on the mechanism of origin of the complementary trisomy cell lines based on molecular cytogenetic studies that showed no evidence for a chimera.