Major histocompatibility complex class II deficiency needs an early diagnosis: report of a case.

Major histocompatibility complex (MHC) class II deficiency is a rare primary immunodeficiency disorder characterized by defects in human leukocyte antigen class II expression, inconsistent expression of human leukocyte class I molecules, and a lack of cellular and humoral immune responses to foreign antigens. Clinical onset occurs early in life with recurrent infections and chronic diarrhea. The prognosis is poor, and mean age at the time of death is 4 years. The only curative treatment is bone marrow transplantation (BMT), which allows the immune system's reconstitution. BMT should be done early in life, because long-term survival seems to depend on the number of previous viral infections. We report the case of an MHC class II deficiency discovered late in a 4-year-old girl by means of immunohistochemistry of small bowel biopsy revealing the absence of MHC class II expression. The child received a BMT twice but died because of a overwhelming viral infection. This case underlines the necessity to explore children presenting with infections and chronic diarrhea in order to find MHC class II deficiency. Usually, diagnosis is performed on cytospins, but when it has been missed clinically, it can be performed by using immunohistochemistry on small bowel biopsies.