Schizoid Personality Disorder (SPD) is a personality disorder characterized by a lack of interest in social relationships, a tendency towards a solitary lifestyle, secrecy, and emotional coldness. SPD can be a precursor to schizophrenia or delusional disorder. The prevalence of the disorder is higher in families with schizophrenia. SPD is not the same as schizophrenia, although it shares some similar traits such as detachment or flat affect.