So, it is likely that “overstimulation” or sensitization of the mesolimbic dopaminergic receptors, rather than the type or dose of DA, concurrently with 5HT2 receptor upregulation, might favor OS development in subjects presenting with biological predisposition to psychiatric disorders [22], as early onset PD (EOPD) patients, consequently leading to abnormal perception and mental representation of environmental inputs, and inappropriate behavior. The gene discussed is HTR2A; the disease is Parkinson disease.