This invention relates to the use of nucleic acid sequences of the MAP kinase-interacting kinase (Mnk) gene family and amino acid sequences encoded thereby, and to using these sequences or effectors of Mnk nucleic acids or polypeptides, particularly Mnk kinase inhibitors and activators, in the diagnosis and treatment of diseases and disorders related to body-weight regulation and thermogenesis. One aspect of the disclosure encompasses methods of identifying an animal or human having an elevated probability of having or developing obesity, the method comprising: (a) obtaining a biological sample from an animal or human subject; and (b) determining from the biological sample whether the animal or human subject has a genetic variant of an Mnk2 and/or Mnk1 gene or a homolog thereof, or an expression product of said Mnk2 and/or Mnk1 gene or homolog thereof, wherein said genetic variant is associated with an elevated probability of having or developing obesity.