TBX1 and 22q11.2 deletion syndrome: On the other hand, the left-right asymmetry is regulated concurrently by another set of genes, LEFTY, PITX2 and NODAL. Aberrations in these pathways can lead to CHD; for example, ZIC3 mutations cause visceral heterotaxy syndromes; TBX1 deletion causes 22q11.2 deletion syndrome/DiGeorge syndrome, associated with conotruncal anomalies such as tetralogy of Fallot (TOF) and interrupted aortic arch [2,18,37-40].