Poland Syndrome is a congenital disorder primarily characterised by the absence of the pectoral muscles on one side of the body.
The cause of Poland Syndrome is still undetermined. The disorder itself has been proven not to be hereditary, usually appearing on a sporadic basis. However, an unusual amount of familial occurrences have encouraged the suggestion that certain events which may lead to the condition could be transmissible.
Evidence from a variety of independent researchers indicates that the most likely cause of Poland Syndrome is a restriction in blood flow through the subclavian artery on one side of the body somewhere between the fifth and seventh week of foetal development.
The subclavian artery runs under the clavicle (collarbone) and feeds blood to the chest muscles, arms and fingers. The left subclavian and right subclavian branch from different parts of the aorta (the largest artery in the human body, originating from the left ventricle of the heart), which could be the reason behind the fact that Poland Syndrome is more common on the right side of the body than the left.
It has been proposed that interruption to blood flow through the subclavian artery could transpire for one of two reasons:
Subclavian Malformation -
The first suggestion is that a disruption occurs due to a malformation of the vessel itself resulting in reduced blood flow to the developing tissues. A misshapen subclavian artery could diminish the blood flow to the chest, arm and hand on the affected side for the duration of the pregnancy. Therefore, the severity of the Poland Syndrome with which the baby is born, or indeed the clinical manifestation (i.e. whether the child is born with Poland Syndrome or another related disorder) would depend on the severity of the vessel malformation and resulting reduction of blood flow to the dependent structures.
Subclavian Artery Supply Disruption Sequence -
The other proposed cause of interrupted blood flow to the chest is Subclavian Artery Supply Disruption Sequence (SASDS), which would involve another physical element putting pressure on the blood flow through the artery. The reason for SASDS is unknown, though it is thought that it could occur as a result of the forward and/or upward growth of the ribs forcing the subclavian artery to become misshapen. It is suggested, in this case, that the specific region of vessel involvement would dictate the ultimate shape of the artery, thus affecting the amount of reduction in blood flow.
In 2000, Dr. D. B. Stevens at Shriners Hospital, Kentucky, USA confirmed, through a detailed study on identical twins, that Poland Syndrome in itself is not an hereditary condition, or one that has arisen from external factors during pregnancy. Numerous DNA tests proved that the twins were genetically identical, however only one displayed features of Poland Syndrome. This firmly negates a genetic source for the disorder and furthermore, since the embryo, foetus and newborn had been exposed to identical physical and chemical conditions, no environmental sources were implicated.
In some cases, however, there may be an inherited predisposition to events such as SASDS causing Poland Syndrome to occur in more than one member of a family. Little more is known about familial Poland Syndrome at this stage.