Derivative Complex Small Supernumerary Marker Chromosomes (sSMC) Involving Chromosomes 2 and 15-A Novel Report

Small supernumerary marker chromosomes (sSMC) constitute a rare group of structural chromosomal abnormalities characterized by additional genetic material that cannot be identified by conventional banding cytogenetics. The incidence of sSMC is extremely rare, and most are expected to have no clinical phenotypic abnormalities. Advanced cytogenetic modalities are crucial for sSMCs identification, characterization, and analysis of chromosomal structure. An 8-day-old neonate born to a G2P2 mother with gestational diabetes and a history of infertility was admitted for respiratory distress. Clinical evaluations included chromosomal microarray, karyotyping, fluorescence in situ hybridization (FISH), brain magnetic resonance imaging (MRI), and cardiac computed tomography (CT). Initial echocardiography revealed atrial and ventricular septal defects, patent ductus arteriosus, and left pulmonary artery stenosis. Brain MRI showed trigonocephaly, ventriculomegaly, corpus callosum dysgenesis, and gray matter heterotopia. Chromosomal microarray identified proximal duplication of 15q and duplication of 2p. Despite intensive care and surgical interventions, the infant faced recurrent respiratory complications and failed extubation attempts. SMC involving chromosomes 15 and 2 presenting with multiple congenital anomalies delineate the genotype-phenotype correlation roadmap. Rapid and immense development in cytogenetics may expand further correlation strategies in the future.