"Histiocytosis X" = any of a group of disorders of unknown cause characterized by histiocytic proliferation, including Hand-Schüller-Christian disease.
Histiocytosis X has typically been thought of as a cancer-like condition. More recently researchers have begun to suspect that it is actually an autoimmune phenomenon, in which immune cells mistakenly attack the body, rather than fight infections. Extra immune cells may form tumors, which can affect various parts of the body including the bones, skull, and other areas.
Some forms of the disorder are genetic.
Histiocytosis X is thought to affect roughly 1 in 200,000 people each year. It is most often seen in children age 1 to 15. The rate peaks among children age 5 to10.
Children over 5 years old often have only bone involvement.
Young children, especially infants, are more likely to have body-wide symptoms that lead to death.
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