The link between SzPD and being underweight may also point to the involvement of biological factors.In general, prenatal caloric malnutrition, premature birth and a low birth weight are risk factors for having a mental disorder and may contribute to the development of SzPD as well. Those who have experienced traumatic brain injury may be also at risk of developing features reflective of SzPD.Other historical researchers had hypothesized excessively perfectionist, unloving or neglectful parenting could play a role. Diagnosis
DSM-5 criteria
The Diagnostic and Statistical Manual of Mental Disorders is a widely used manual for diagnosing mental disorders. DSM-5 includes SzPD with the same criteria as in DSM-IV. In the DSM-5, SzPD is described as a pervasive pattern of detachment from social relationships and a restricted range of expression of emotions in interpersonal settings, beginning by early adulthood and present in a variety of contexts, as indicated by at least four of the following:
Neither desires nor enjoys close relationships, including being part of a family. Almost always chooses solitary activities. Has little, if any, interest in having sexual experiences with another person. Takes pleasure in few, if any, activities. Lacks close friends or confidants other than first-degree relatives. Appears indifferent to the praise or criticism of others. Shows emotional coldness, detachment, or flattened affectivity.According to the DSM, those with SzPD may often be unable to, or will rarely express aggressiveness or hostility, even when provoked directly. These individuals can seem vague or drifting about their goals and their lives may appear directionless.
"Only schizoid patients", suggests Klein, "who have worked through the abandonment depression ... ultimately will believe that the capacity for relatedness and the wish for relatedness are woven into the structure of their beings, that they are truly part of who the patients are and what they contain as human beings. It is this sense that finally allows the schizoid patient to feel the most intimate sense of being connected with humanity more generally, and with another person more personally. For the schizoid patient, this degree of certainty is the most gratifying revelation, and a profound new organizer of the self experience. ": 127

Development and course
SzPD can be first apparent in childhood and adolescence with solitariness, poor peer relationships and underachievement in school. This may mark these children as different and make them subject to teasing.Being a personality disorder, which is usually chronic and long-lasting mental conditions, SzPD is not expected to improve with time without treatment; however, much remains unknown because it is rarely encountered in clinical settings. Epidemiology
SzPD is uncommon in clinical settings (about 2.2%) and occurs more commonly in males. It is rare compared with other personality disorders, with a prevalence estimated at less than 1% of the general population.Philip Manfield suggests that the "schizoid condition", which roughly includes the DSM schizoid, avoidant and schizotypal personality disorders, is represented by "as many as forty percent of all personality disorders."