Characterization of sSMC by FISH and molecular techniques

Small supernumerary marker chromosome (sSMC) is a structurally altered additional chromosome that may not be explicitly clarified by conventional karyotyping alone. About one third of sSMC carriers have abnormal phenotypes and its clinical correlation is difficult, especially in prenatal studies. The present study was aimed at characterizing 19 sSMC identified in 15 patients with dysmorphic features with or without multiple congenital anomalies, conspicuous family history, short stature and/or ambiguous genitalia. All the sSMC were primarily identified by routine cytogenetics studies (performed with banding techniques) from peripheral blood except in one patient, where amniotic fluid was used. All sSMCs were further characterized by array-CGH (using 44 K oligonucleotide probe) and/or fluorescence in situ hybridization (FISH) using multicolor banding (MCB), centromere specific multicolor FISH (cenM-FISH), subcentromere-specific multicolor FISH (subcenM-FISH), micro-dissection and/or reverse FISH. This report demonstrates the worth of advanced molecular (cyto)genetic techniques in characterizing sSMC, their utility in genotype-phenotype correlation and risk of clinical presentation.