Mosaic tetrasomy 9p in a girl with multiple congenital anomalies: cytogenetic and molecular-cytogenetic studies

We report on a 16-year-old girl with tetrasomy 9p mosaicism. Clinical inves tigations disclosed a malformation syndrome with craniofacial abnormalities , dysplasia of the right clavicle, short neck with cervical ribs, patella d islocation, Dandy-Walker malformation, mental retardation and blindness. Ka ryotype analysis of blood lymphocytes indicated an additional marker in the size of a C-group chromosome with a large heterochromatic block in 88% of the investigated metaphases. The origin and structure of this additional ma rker could not be determined by chromosome banding. Application of fluoresc ence in situ hybridisation and comparative genomic hybridisation identified the origin of the marker chromosome, demonstrating the effectiveness of mo lecular-cytogenetic investigations in the diagnosis of structural and numer ical chromosome abnormalities.