STYXL2 is an atypical dual-specificity phosphatase (DUSP) that dephosphorylates both phosphotyrosine and phosphoserine/phosphothreonine residues 1. As a cytosolic enzyme highly expressed in skeletal muscle, liver, and adipose tissue 2, STYXL2 functions as a negative regulator of MAPK cascades, consistent with its phosphatase activity 1. The protein appears structurally similar to other small DUSPs like DUSP13 and VHR 2. In myogenesis, STYXL2 (also known as DUSP27) acts as a key regulator of muscle stem cell fate transition from proliferation to differentiation, with MyoD directly targeting this phosphatase during myogenic commitment 3. Overexpression of related DUSP family members promotes premature muscle differentiation, supporting a role in myofiber maturation 3. STYXL2 also contributes to skeletal muscle insulin sensitivity through AMPK activation 4. Additionally, STYXL2 variants have been associated with heroin addiction vulnerability in African American populations 5, suggesting broader physiological importance beyond muscle biology. These findings indicate STYXL2 functions as a critical signaling regulator in energy metabolism and muscle development with potential disease relevance in metabolic and neurobiological conditions.