Report on 3 patients with 12p duplication including GRIN2B.

The duplication of the short arm (p) of chromosome 12 is a rare chromosomal abnormality, and most reported cases result from malsegregation of a balanced parental translocation associated with other chromosomal imbalances. Of the reported cases, only 15 involve a pure and complete 12p duplication and only 10 involve a pure and partial duplication overlapping the 12p12.3p13.1 region, including a single instance of an inherited duplication in two related individuals. Here, we report three new patients with a pure 12p duplication, detected by conventional cytogenetic studies and characterized by array-comparative genomic hybridization (array-CGH) and fluorescence in situ hybridization (FISH). The first patient was a child carrying a de novo inverted duplication of the short arm of chromosome 12. His phenotype was similar to that of the "trisomy 12p syndrome", characterized by developmental delays and craniofacial abnormalities including a high forehead, a short nose with anteverted nostrils and an everted lower lip. The second and third patients were a mother and son with a direct 12p12.3p13.1 duplication, exhibiting a milder phenotype characterized by moderate developmental delays, dysmorphic facial features, behavioral problems and obesity. The present data, including the rarity of the familial cases, should contribute to our knowledge of the genotype/phenotype correlation in trisomy 12p patients.