Taijin Kyofusho is a "culturally distinctive phobia in Japan." (DSM-IV) It resembles social phobia or anthrophobia.
I guess many Japanese children with selective mutism are comorbid with Taijin Kyofusho. According to the literature in the West, most children with selective mutism have social phobia. In addition, I've seen former mutism sufferers who seem to have Taijin Kyofusho on the Internet.
But as far as I know, few Japanese researchers point out the relationship between selective mutism and Taijin Kyofusho.
Unlike researchers in the West, Japanese researchers aren't interested in the relationship between selective mutism and anxiety disorder very much. Some Japanese researchers cite the literature in the West and argue most children with selective mutism have anxiety disorder or selective mutism is an anxiety disorder. But as far as I know, none of them research on them by themselves.
Index of SM in Japan