TBX1 and Atrioventricular canal defect: These included a deletion on 22q11.2, which is smaller than the typically deleted region in 22q11.2 deletion syndrome, not overlapping TBX1 but encompassing CRKL, which has been proposed as an independent causative gene for CHD in the 22q11.2 region,13 found in a patient with isolated ventricular septal defect (Figure 2C); and a duplication of two adjacent regions on chromosome 5 encompassing the genes FLT4 and NSD1 (partially) in a patient with isolated atrioventricular septal defect (Figure 2D), of which FLT4 duplication has been reported in TOF.6,7,14