<unk> , previously known as Hand–Schüller–Christian disease, is a type of<unk> <unk><unk>  (LCH), which can affect multiple organs. The condition is traditionally associated with a combination of three features; bulging eyes, breakdown of bone (lytic bone lesions often in the skull), and diabetes insipidus (excessive thirst and passing urine), although around 75% of cases do not have all three features. Other features may include a fever and weight loss, and depending on the organs involved there maybe rashes, asymmetry of the face, ear infections, signs in the mouth and the appearance of advanced gum disease. Features relating to lung and liver disease may occur. It is due to a genetic mutation in the MAPKinase pathway that occurs during early development. The diagnosis may be suspected based on symptoms and MRI and confirmed by tissue biopsy. Blood tests may show anaemia, and less commonly a low white blood<unk>  count and low platelet count. Treatment may involve surgery, chemotherapy, radiation therapy, and certain medicines. Hand–Schüller–Christian disease was named for the American pediatrician Alfred Hand Jr., the Austrian neuroradiologist Arthur Schüller, and the American internist Henry Asbury Christian, who described it in 1893, 1915 and 1919, respectively. Before the Histiocyte Society classified<unk>  in the 1980s, the condition was also known as<unk>  X", where "X" denoted the then unknown cause. It is now known as<unk> , a subtype of LCH. The disease is rare. Most present between the ages of two and six. The outlook depends on how many and how much organs are affected. In some people the condition is life-threatening.
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