Dr Achim Wuesthof, an endocrinologist specialising in children and adolescents, who is treating the teenager at a clinic in Hamburg, said the procedure had been a success so far. Speaking to The Sunday Telegraph, he said that even though under-16s were not permitted to undergo a sex change in other countries, he and his colleagues felt that in this case it had been best to start earlier. He said: "To the best of my knowledge, Kim is the youngest sex change patient in the world. According to German law, two independent psychiatrists must confirm that the child is indeed transsexual and approve the sex change. Once that has been done, it is best to start as early as possible.