A 3-year-old boy is taken to the pediatrician because of a nosebleed (epistaxis).He has a history of severe,recurrent sinopulmonary infection.Physical examination is remarkable for dry,red patches of skin (eczema)and multiple petechiae (tiny hemorrhagic spots).Laboratory findings include thrombocytopenia and reduced IgM levels.The boy's maternal uncle died of bleeding complications after an emergency appendectomy.Which of the following is the most likely diagnosis?

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Quizplus · Accepted Answer

This patient most likely has Wiskott-Aldrich syndrome (WAS),an X-linked immunodeficiency disease involving multiple organ systems.It is characterized by eczema,a low platelet count (thrombocytopenia),and susceptibility to bacterial infection.Patients with WAS have a mutation in a gene that encodes a cytoplasmic protein expressed exclusively in bone marrow-derived cells.This protein interacts both with adapter molecules,such as Grb-2,and with small G proteins of the Rho family that regulate the actin cytoskeleton.Expression of many cell surface glycoproteins on lymphocytes,macrophages,neutrophils,and platelets is also reduced.All of these changes likely interfere with trafficking of leukocytes to sites of inflammation.

A 3-Year-Old Boy Is Taken to the Pediatrician Because of a Nosebleed