[Strategies to identify supernumerary chromosomal markers in constitutional cytogenetics]

Supernumerary marker chromosomes (SMCs) are defined as extrastructurally abnormal chromosomes which origin and composition cannot be determined by conventional cytogenetics. SMCs are an heterogeneous group of abnormalities concerning all chromosomes with variable structure and size and are associated with phenotypic heterogeneity. The characterisation of SMCs is of utmost importance for genetic counselling. Different molecular techniques are used to identify chromosomal material present in markers such as 24-colour FISH (MFISH, SKY), centromere specific multicolour FISH (cenMFISH) and derivatives (acroMFISH, subcenMFISH), comparative genomic hybridisation (CGH), arrayCGH, and targeted FISH techniques (banding techniques, whole chromosome painting...). Based on the morphology of SMC with conventional cytogenetic and clinical data, we tried to set up different molecular strategies with all available techniques.