Somatic symptom disorder (SSD) and antisocial personality disorder (APSD) are found at higher rates within families compared to the general population. Both disorders are characterized by low serotonin levels, which may be attributed to polymorphisms in the dopa decarboxylase (DDC) gene. The polymorphism rs11575542 of the gene leads to decreasing the efficiency of aromatic l-amino decarboxylase (AADC) and serotonin levels in a person. The polymorphism is also associated with the development of somatic symptoms and sensation-seeking behavior, a trait underlying APSD. Hence, the role of this polymorphism as an underlying feature that may predispose a person to develop APSD or SSD should be explored further in future studies.