Taken together, our data show that neuroblastoma-associated Alk point mutations do not result in changes in NB number, or in gross increases in proliferation, but rather perturb neuronal fate specification, which leads to precocious Mamo expression in the γ-cell lineage of AlkY1355S mutant wL3 brains that persists until adult stages. This evidence concerns the gene ALK and neuroblastoma.