Abstract: Interleukin 7 (IL-7) is a critical cytokine that plays a fundamental role in B- and T-cell development and in acute lymphoblastic leukemia (ALL). Its receptor (IL7R) is a transmembrane heterodimer formed by the IL7R alpha and the IL2R gamma chain (gamma c). The IL7R signals through the JAK/STAT pathway. Loss-of-function mutations and some polymorphisms of the IL7R alpha were associated to immunodeficiency and inflammatory diseases, respectively. Gain-of-function mutations were described in T-cell ALL and in high risk precursor B-cell ALL. Most confirmed loss-of-function mutations occur in the extracellular part of the IL7R alpha while oncogenic mutations are exclusively found in the extracellular juxtamembrane (EJM) or transmembrane regions. Oncogenic mutations promote either IL7R alpha/IL7R alpha homodimerization and constitutive signaling, or increased affinity to gamma c or IL-7. This work presents a review on IL7R alpha polymorphisms/mutations and attempts to present a classification based on their structural consequences and resulting biological activity Ver menos