ALK and Nijmegen breakage syndrome: Similarly, familial NBs, which account for 2%–3% of all NB cases, are associated with highly penetrant germline activation alterations in the anaplastic lymphoma kinase gene (80% of familial NBs cases) or inactivating mutations in the PHOX2B gene (encoding the transcription factor paired mesoderm homeobox protein 2B).7, 8