Anything that causes further narrowing has the tendency to impinge the tendon and cause an inflammatory response, resulting in impingement syndrome. Such causes can be  bony structures such as subacromial spurs (bony projections from the acromion), osteoarthritic spurs on the acromioclavicular joint, and variations in the shape of the acromion. Thickening or calcification of the coracoacromial ligament can also cause impingement. Loss of function of the rotator cuff muscles, due to injury or loss of strength, may cause the humerus to move superiorly, resulting in impingement. Inflammation and subsequent thickening of the subacromial bursa may also cause impingement.Weight training exercises where the arms are elevated above shoulder height but in an internally rotated position such as the upright row have been suggested as a cause of subacromial impingement. Another common cause of Impingement syndrome is restrictions in the range movement of the scapulo-thoracic surfaces. Commonly, one or more ribs between rib 2 and rib 7/8 on the side of the impingement may jut out slightly and/or feel hard when the person springs on it or them. When this occurs, the scapula is raised and anteverted (angled forwards). This in turn pushes the acromion and the humeral head out of its usual anatomical position placing pressure downwards at the head of the humerus at the position of the nerve thus causing the impingement syndrome. This is visibly demonstrated by a slightly raised and protracted shoulder girdle.
In July 2006, the United States Food and Drug Administration approved a synthetic version of I2S produced by Shire Pharmaceuticals Group, called Elaprase, as a treatment for MPS type II (Hunter syndrome). Vestronidase alfa (Mepsevii) is a recombinant human lysosomal beta glucuronidase for MPS VII (Sly syndrome) approved in the United States in November 2017 (Ultragenyx).Bone marrow transplantation (BMT) and umbilical cord blood transplantation (UCBT) have had limited success in treating the mucopolysaccharidoses. Abnormal physical characteristics, except for those affecting the skeleton and eyes, may be improved, but neurologic outcomes have varied. BMT and UCBT are high-risk procedures and are usually performed only after family members receive extensive evaluation and counseling. See also
Alder-Reilly anomaly — a morphologic abnormality of white blood cells associated with mucopolysaccharidosis
Lysosomal storage disease

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