First report of a partial trisomy 3q12-q23 de novo--FISH breakpoint determination and phenotypic characterization.

We present a 1-year-old boy with mild mental retardation, postnatal growth retardation, and facial dysmorphisms such as frontal bossing, laterally accentuated bushy eyebrows, deep set eyes with long lashes, hypertelorism, and a broad nasal bridge. Except for hip dysplasia, no congenital malformations were detected. By conventional cytogenetics a derivative chromosome 3 de novo was diagnosed which was identified as tandem dup(3)(q12q23) by fluorescence in situ hybridization (FISH) applying arm specific paints and eight different YAC-probes. The duplicated segment lies proximally from the reported dup(3q) syndrome critical region, thus explaining the absence of characteristic phenotypic features of dup(3q) syndrome. To our knowledge this is the first report of a patient with pure trisomy of this proximal region of the long arm of chromosome 3.