Hyper-IgM Syndrome (HIM) is a rare genetic (primary) immunodeficiency disorder that is typically inherited as an X-linked recessive genetic trait. Symptoms and physical findings associated with the disorder usually become apparent in the first or second year of life. Hyper-IgM Syndrome may be characterized by recurrent pus-producing (pyogenic) bacterial infections of the upper and lower respiratory tract including the sinuses (sinusitis) and/or the lungs (pneumonitis or pneumonia); the middle ear (otitis media); the membrane that lines the eyelids and the white portions (sclera) of the eyes (conjunctivitis); the skin (pyoderma); and/or, in some cases, other areas. Individuals with Hyper-IgM Syndrome are also susceptible to "opportunistic" infections, i.e., infections caused by microorganisms that usually do not cause disease in individuals with fully functioning immune systems (non-immunocompromised) or widespread (systemic) overwhelming disease by microorganisms that typically cause only localized, mild infections. In individuals with Hyper-IgM Syndrome, such opportunistic infections may include those caused by Pneumocystis carinii, a microorganism that causes a form of pneumonia, or Cryptosporidium, a single-celled parasite (protozoa) that can cause infections of the intestinal tract. In addition, individuals with Hyper-IgM Syndrome are prone to certain autoimmune disorders affecting particular elements of the blood, such as neutropenia, a condition in which there is an abnormal decrease of certain white blood cells (neutrophils). Additional physical findings often associated with the disorder may include enlargement (hypertrophy) of the tonsils, enlargement of the liver and spleen (hepatosplenomegaly), chronic diarrhea and impaired absorption of nutrients by the intestinal tract (malabsorption), and/or other symptoms.
The range and severity of symptoms and physical features associated with this disorder may vary from case to case. Because approximately 70 percent of reported cases of Hyper-IgM Syndrome are inherited as an X-linked recessive genetic trait, the vast majority of affected individuals are male. However, some cases of autosomal recessive and autosomal dominant genetic inheritance have been reported. In addition, a rare acquired form of the disorder has been described in the medical literature.