Histiocytosis-lymphadenopathy plus syndrome

Histiocytosis-lymphadenopathy plus syndrome (also known as SLC29A3 spectrum disorder) is a group of conditions with overlapping signs and symptoms that affect many parts of the body. This group of disorders includes H syndrome, pigmented hypertrichosis with insulin-dependent diabetes mellitus (PHID), Faisalabad histiocytosis, and familial Rosai-Dorfman disease (RDD). These conditions were once thought to be distinct disorders; however, because of the overlapping features and shared genetic cause, they are now considered to be part of the same disease spectrum. While some affected individuals have signs and symptoms characteristic of one of the conditions, others have a range of features from two or more of the conditions. The pattern of signs and symptoms can vary even within the same family.

A feature common to the disorders in this spectrum is histiocytosis, which is the overgrowth of immune system cells called histiocytes. The cells abnormally accumulate in one or more tissues in the body, which can lead to organ or tissue damage. The buildup often occurs in the lymph nodes, leading to swelling of the lymph nodes (lymphadenopathy). Other areas of cell accumulation can include the skin, kidneys, brain and spinal cord (central nervous system), or digestive tract.

This spectrum is known as histiocytosis-lymphadenopathy plus syndrome because the disorders that make up the spectrum can have additional signs and symptoms. A characteristic feature of H syndrome is abnormal patches of skin (lesions), typically on the lower body. These lesions are unusually dark (hyperpigmented) and have excessive hair growth (hypertrichosis). In addition, histiocytes accumulate at the site of the skin lesions. Other features of H syndrome include enlargement of the liver (hepatomegaly), heart abnormalities, hearing loss, reduced amounts of hormones that direct sexual development (hypogonadism), and short stature.

Like H syndrome, PHID causes patches of hyperpigmented skin with hypertrichosis. PHID is also characterized by the development of type 1 diabetes (also known as insulin-dependent diabetes mellitus), which usually begins in childhood. Type 1 diabetes occurs when the body does not produce enough of the hormone insulin, leading to dysregulation of levels of blood glucose, also called blood sugar.

Faisalabad histiocytosis typically causes lymphadenopathy and swelling of the eyelids due to accumulation of histiocytes. Affected individuals can also have joint deformities called contractures in their fingers or toes and hearing loss.

The most common feature of familial RDD is lymphadenopathy, usually affecting lymph nodes in the neck. Histiocytes can also accumulate in other parts of the body. (Familial RDD is one of several forms of RDD; the other forms are not considered part of histiocytosis-lymphadenopathy plus syndrome.)