WHAT is Poland syndrome?

Poland syndrome is a disorder in which affected individuals are born with missing or underdeveloped muscles on one side of the body, resulting in abnormalities that can affect the chest, shoulder, arm, and hand.
The extent and severity of the abnormalities vary among affected individuals.
Many people with Poland syndrome have hand abnormalities on the affected side.
Commonly including an underdeveloped hand with abnormally short fingers (brachydactyly); small, underdeveloped (vestigial) fingers; and some fingers that are fused together (syndactyly).
This combination of hand abnormalities is called symbrachydactyly.
Some affected individuals have only one or two of these features, or have a mild hand abnormality that is hardly noticeable; more severe abnormalities can cause problems with use of the hand. 
It has been estimated to occur in 1 in 20,000 newborns.
For unknown reasons, this disorder occurs more than twice as often in males than in female.
The cause the syndrome is unknown, but researchers have suggested it may result from a disruption of blood flow during development before birth.

Source: National Institute of Health