[Concordant myaplasia of the thoracic wall in monozygotic twins (Poland anomaly)].

A set of monozygotic twins affected with unilateral shoulder girdle muscle aplasia is reported. One twin showed Poland-like aplasia of the pectoralis but without the ipsilateral dysmelia, the other aplasia of dorsal spinothoracic muscles. The controversy about exogenous or genetic causes of the Poland anomaly and the whole spectrum of shoulder myaplasia may be solved assuming a multifactorial origin. The striking sex distribution and the continuous range of symptoms observed are in keeping with this hypothesis.