Protein TFG (TRK-fused gene protein) plays a role in regulating phosphotyrosine-specific phosphatase-1 activity. Mutations in TFG may have important clinical relevance for current therapeutic strategies to treat metastatic melanoma. Defects in TFG are a cause of thyroid papillary carcinoma (TPC), a common tumor of the thyroid that typically arises as an irregular, solid or cystic mass from otherwise normal thyroid tissue. Recent genetic investigation indicates that formation of TFG-containing cytoplasmic inclusions and concomitant mislocalization of TAR DNA-binding protein 43 kDa (TDP-43) underlie motor neuron degeneration in HMSN-P. Pathological overlap of proteinopathies involving TFG and TDP-43 highlights a new pathway leading to motor neuron degeneration.