There are 80 variant alleles for CYP2D6 which have been discovered while CYP2D6 gene polymorphisms are also a contributing factor in developing SS and for patients with genetic CYP3A4 variants the excessive level even treated with a normal therapeutic dose was reported too.[26] As to our case, the patient seems susceptible to Paroxetine, since he presented AE immediately after the Paroxetine intake, Paroxetine is reported to be the most potent CYP2D6 inhibitor of all antidepressants [27] when coadministered with drugs possessing serotonergic activity, the drug levels may increase to cause SS. Here, CYP3A4 is linked to synovial sarcoma.