Chromosome 5 derived small supernumerary marker: towards a genotype/phenotype correlation of proximal chromosome 5 imbalances

Small supernumerary marker chromosomes (sSMC) are a morphological heterogeneous group of additional abnormal chromosomes that cannot be characterized alone by conventional banding cytogenetics. Molecular cytogenetic techniques are valuable tools for the accurate identification of sSMC and a prerequisite for sound genetic counseling based on refined genotype/phenotype correlation. We describe a new case of a retarded patient with an sSMC derived from chromosome 5. The characterization of the sSMC was done by subcentromere-specific multicolor (subcenM) fluorescence in-situ hybridization (FISH) and by full tilling resolution array analysis, after microdissection and amplification of the marker DNA. Uniparental disomy for normal sister chromosomes of the sSMC(5) was excluded. The karyotype was mos47,XX,+r(5)(::p11.1 -> aEuro parts per thousand q12.1::)[70%]/46,XX[30%], being the trisomic region between 46.15 similar to 49.56 Mb and 61.25 similar to 61.335 Mb, a region known to harbor similar to 45 annotated genes. Together with a review of the previously described cases of sSMC(5) and duplications involving the 5q proximal region, we can conclude that trisomy of the 5q11 region is associated with learning difficulties and speech delay.