[Concordant medullary thyroid carcinoma in identical twins with discordant phaeochromocytoma (Sipple syndrome) (author's transl)].

The first case of Sipple syndrome in identical twins is reported. It is concluded that the concordant medullary carcinoma of the thyroid is the result of a germinal mutation, whilst the discordant solitary phaeochromocytoma is caused by a somatic mutation according to the two mutation model. The practical conclusion to be drawn from this report is that if one identical twin develops carcinoma of the thyroid or a phaeochromocytoma, the other twin should be throughly investigated and surgical exploration undertaken, even in the absence of clinical evidence of disease.