All three patients with bilateral triphalangeal thumb harboured an identical substitution in the ZRS of SHH. 21 Only two other patients in the cohort had triphalangeal thumb, and in neither case was the malformation bilateral; one patient had unilateral triphalangeal thumb associated with ipsilateral preaxial polydactyly and a mutation in SALL1,22 the other had triphalangeal thumb associated with tetralogy of Fallot, and no identified mutation. This evidence concerns the gene SALL1 and Tetralogy of Fallot.