Supernumerary marker chromosomes (SMCs) lacking alpha-satellite sequences and possessing a newly derived functional centromere are referred to as neocentromere marker chromosomes (NMCs). Although the delineation of the chromosome content of these NMCs would be helpful for genetic counseling, such fine mapping has been difficult because of the limited sizes of the involved segments. We report on a female patient with mosaic NMC involving 3q26.3-3qter, the content of which was determined using an array CGH analysis. Our results support the validity of an array CGH-based approach to investigating the origins of SMCs. Further FISH analyses revealed that the NMC is characterized by an asymmetric inv-dup structure separated by a single-copy region. The present case had many manifestations of dup(3q) syndrome, the critical interval of which is considered to be 3q26.3-q27. Common features included mental and growth retardation, hirsutism, synophrys, a broad nasal root, anteverted nares, downturned corners of the mouth, and malformed ears. The observation gives further credence to the concept that the critical region responsible for the dup(3q) phenotype to 3q26.3-q27.
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