Tehran University of Medical Sciences Iranian Journal of Allergy, Asthma and Immunology 1735-1502 1 3 2000 08 15 147 152 A. Farhoudi L. Atarod B. Ghazl A. Ahmadi Afshar 2015 10 01 Hyper IgM syndrome (HIM SX) is a rare congenital primary immunodeficiency that affects males more than females (70%, x-Iinked recessive), but there are reports of autosomal recessive and autosomal dominant inheritances. In this study, we review medical histories of 2 affected girls and one affected boy. Our 3 cases fulfill clinical and laboratory criteria of this syndrome. Their clinical signs include recurrent pyogenic and opportunistic infections especilly in skin, respiratory and GI tracts, case 2 suffered from recurrent urinary tract infections too. Case 3 experienced P. carinii pnemonia during a severe neutropenic episode. Other signs were 1- Autoimmunities as neutropenia, throbocytopenia, Coomb's positive hemolytic anemia and chronic parotitis in second case, 2- lymphoid hyperplasia presenting as generalized lymphadenopathies, hepatosplenomegaly and nodular lymphoid hyperplasia of intestine. Case 3, the 5 year old boy had an ataxic gait and suffered from recurrent herpetic keratoconjunctivitis and stomatitis. All the cases had very high serum levels of IgM (>1000 mg/dl) while other immunoglobulins were low. Sm IgM -f B lymphocytes were increased in the first two cases and CD40L on Tcell of the 3rd case was absent. Occurance of this syndrome in girls is a very rare phenomenon. Presence of high or normal serum IgM level in a hypogammaglobulinemic patient should be a clue for diagnosing this syndrome and could be further confirmed either by studying CD40L/CD40 pathway or through a genetic survey. https://ijaai.tums.ac.ir/index.php/ijaai/article/view/23 https://ijaai.tums.ac.ir/index.php/ijaai/article/download/23/23