Classically, patients with<unk>  will suffer from recurrent bouts of infection due to the decreased capacity of their immune system to fight off<unk> -causing organisms. The recurrent infections they acquire are specific and are, in decreasing order of frequency: * pneumonia * abscesses of the skin, tissues, and organs * septic arthritis * osteomyelitis * bacteremia/fungemia * superficial skin infections such as cellulitis or impetigo Most people with<unk>  are diagnosed in childhood, usually, before age 5. Early diagnosis is important since these people can be placed on antibiotics to ward off infections before they occur. Small groups of<unk>  patients may also be affected by McLeod syndrome because of the proximity of the two genes on the same X-chromosome. Atypical infections Microscopic image of the fungus, Aspergillus fumigatus, an organism that commonly causes<unk>  in people with<unk> . People with<unk>  are sometimes infected with organisms that usually do not cause<unk>  in people with normal immune systems. Among the most common organisms that cause<unk>  in<unk>  patients are: * Bacteria (particularly those that are catalase-positive) * Staphylococcus aureus. * Serratia marcescens. * Listeria species. * E. coli. * Klebsiella species. * Pseudomonas cepacia, a.k.a. Burkholderia cepacia. * Nocardia. * Fungi * Aspergillus species. Aspergillus has a propensity to cause infection in people with<unk>  and of the Aspergillus species, Aspergillus fumigatus seems to be most common in<unk> . * Candida species. Patients with<unk>  can usually resist infections of catalase-negative bacteria but are susceptible to catalase-positive bacteria. Catalase is an enzyme that catalyzes the breakdown of hydrogen peroxide in many organisms. In infections caused by organisms that lack catalase (catalase-negative), the host with<unk>  is successfully able to "borrow" hydrogen peroxide being made by the organism and use it to fight off the infection. In infections by organisms that have catalase (catalase-positive), this "borrowing mechanism" is unsuccessful because the enzyme catalase first breaks down any hydrogen peroxide that would be borrowed from the organism. Therefore in the<unk>  patient, hydrogen peroxide cannot be used to make oxygen radicals to fight infection, leaving the patient vulnerable to infection by catalase-positive bacteria.
Chronic granulomatous disease
Common variable immunodeficiency
Wiskott–Aldrich syndrome
Severe combined immunodeficiency
Primary immunodeficiency
X-linked agammaglobulinemia
Selective immunoglobulin A deficiency
SAPHO syndrome