Immunodeficiency-27A (IMD27A) results from autosomal recessive (AR) IFNGR1 deficiency. Patients with complete IFNGR1 deficiency have a severe clinical phenotype characterized by early and often fatal mycobacterial infections. The disorder can thus be categorized as a form of mendelian susceptibility to mycobacterial disease (MSMD). Bacillus Calmette-Guerin (BCG) and environmental mycobacteria are the most frequent pathogens, and infection typically begins before the age of 3 years. Plasma from patients with complete AR IFNGR1 deficiency usually contains large amounts of IFNG (147570), and their cells do not respond to IFNG in vitro. In contrast, cells from patients with partial AR IFNGR1 deficiency, which is caused by a specific mutation in IFNGR1, retain residual responses to high IFNG concentrations. Patients with partial AR IFNGR1 deficiency are susceptible to BCG and environmental mycobacteria, but they have a milder clinical disease and better prognosis than patients with complete AR IFNGR1 deficiency. The clinical features of children with complete AR IFNGR1 deficiency are usually more severe than those in individuals with AD IFNGR1 deficiency (IMD27B), and mycobacterial infection often occurs earlier (mean age of 1.3 years vs 13.4 years), with patients having shorter mean disease-free survival. Salmonellosis is present in about 5% of patients with AR or AD IFNGR1 deficiency, and other infections have been reported in single patients (review by Al-Muhsen and Casanova, 2008).

Immunodeficiency-27B (IMD27B) results from autosomal dominant (AD) IFNGR1 deficiency. Patients with AD IFNGR1 deficiency commonly present with recurrent, moderately severe infections with environmental mycobacteria or bacillus Calmette-Guerin (BCG). In contrast with patients with complete autosomal recessive (AR) IFNGR1 deficiency (IMD27A), cells from patients with AD IFNGR1 deficiency display residual responses to IFNG in vitro, indicating that the deficiency in IFNGR1 is partial. The clinical features of AD IFNGR1 deficiency are usually less severe than those in children with complete AR IFNGR1 deficiency, and mycobacterial infection often occurs later (mean age of 13.4 years vs 1.3 years), with patients having longer mean disease-free survival. In patients with AD IFNGR1 deficiency, M. avium tends to cause unifocal or multifocal osteomyelitis. Salmonellosis is present in about 5% of patients with AR or AD IFNGR1 deficiency, and other infections have been reported in single patients (review by Al-Muhsen and Casanova, 2008).