Discordant phenotypes in monozygotic twins with 16p11.2 microdeletions including the SH2B1 gene.

A 200∼240 kb SH2B1-containing deletion region on 16p11.2 is associated with early-onset obesity and developmental delay. Here, we describe monozygotic twin brothers with discordant clinical presentations. Intrauterine fetal growth restriction was present in both twins. Additionally, twin A exhibited coarctation of aorta, left ventricular noncompaction, atrial septal defect, pericardial effusion, left hydronephrosis, and moderate developmental delay, whereas twin B exhibited single umbilical artery. Chromosome microarray analysis was performed on both twins and their parents. An identical 244 kb microdeletion on 16p11.2 including 9 Refseq genes, including SH2B1, was identified in the twins. The novel findings in monozygotic twins may expand the phenotypic spectrum of 16p11.2 microdeletion. Further studies are needed to strengthen the correlation between genotypes and abnormal clinical features.