Poland syndrome is marked by a unilateral absence or hypoplasia of the pectoralis major muscle (most frequently involving the sternocostal portion), and a variable degree of ipsilateral hand anomalies, including symbrachydactyly. Various anomalies of the breasts and nipples, and variable involvement of the hand and forearm (some patients having normal hands) have also been reported. The absence of other muscles around the shoulder girdle is a frequent feature. The syndrome is thought to be of vascular origin, for example a result of a disruption in the blood supply in the subclavian artery. Poland syndrome is most commonly a sporadic condition, but rare familial cases have been reported, compatible with an autosomal dominant mode of inheritance.