What personality disorder involves a lack of interest in social relationships and a restricted range of emotional expression?

The personality disorder characterized by a lack of interest in social relationships and a restricted range of emotional expression is indeed Schizoid Personality Disorder. Individuals with this disorder typically prefer solitary activities and often show little emotional expression in social settings. They tend to be detached from social relationships, demonstrating indifference to praise or criticism from others.

In contrast, the other options highlight different characteristics that do not align with the definition provided. Schizotypal Personality Disorder involves eccentric behaviors and beliefs, often manifesting as social anxiety but still having some interest in relationships. Avoidant Personality Disorder is marked by a strong desire for social interaction but is hindered by feelings of inadequacy and hypersensitivity to negative evaluation. Dependent Personality Disorder is characterized by an excessive need for care and approval from others, contrasting sharply with the emotional detachment seen in Schizoid Personality Disorder. Therefore, the defining traits of Schizoid Personality Disorder make it the correct choice for this question.