The 13 diagnostic infant samples were screened for the known recurrent mutations in T‐ALL, including NOTCH1, FBXW7, PTEN and IL7R (detailed mutation data is shown in Table SII), as well as KRAS, NRAS mutations, STIL‐TAL1 fusion and the presence of TLX3. Results showed four cases were mutated for NOTCH1, two being mutated in the HD domain only (BR1 and FR4), one in the PEST only (BR6) and one (FR3) with mutations in both HD and PEST. Here, NOTCH1 is linked to acute lymphoblastic leukemia.