It has been shown that there is a two to three fold greater risk of having social phobia if a first-degree relative also has the disorder. This could be due to genetics and/or due to children acquiring social fears and avoidance through processes of observational learning or parental psychosocial education. Studies of identical twins brought up (via adoption) in different families have indicated that, if one twin developed social anxiety disorder, then the other was between 30% and 50% more likely than average to also develop the disorder. To some extent this 'heritability' may not be specific - for example, studies have found that if a parent has any kind of anxiety disorder or clinical depression, then a child is somewhat more likely to develop an anxiety disorder or social phobia. Studies suggest that parents of those with social anxiety disorder tend to be more socially isolated themselves, and shyness in adoptive parents is significantly correlated with shyness in adopted children;
Adolescents who were rated as having an insecure (anxious-ambivalent) attachment with their mother as infants were twice as likely to develop anxiety disorders by late adolescence, including social phobia (SAD)
A related line of research has investigated Behavioral inhibition' in infants - early signs of an inhibited and introspective or fearful nature. Studies have shown that around 10-15% of individuals show this early temperament, which appears to be partly due to genetics. Some continue to show this trait in to adolescence and adulthood, and appear to be more likely to develop social anxiety disorder.