PITX2 and neoplasm: It is therefore noteworthy that 37% of the evaluable MLLT1-mutant tumours (which lacked WT1 mutations and deletions) also had CTNNB1 or WTX mutations, and MLLT1-mutant tumours all show a striking increase in expression of PITX2 (Fig. 2), a gene encoding a homeobox protein whose expression follows canonical Wnt pathway activation and results in increased proliferation during early development48, 49.