561del4 defines a novel small deletion hotspot in the interferon-gamma receptor 1 chain.

Patients with a dominant small deletion (818del4, hotspot) in the interferon-gamma receptor 1 (IFNGR1) gene (6q23-q24) and increased susceptibility to mycobacterial infections have been recently reported. We describe a female patient homozygous for a 4-bp deletion in exon 5 of IFNGR1 (561del4) who developed postvaccinal disseminated Bacille Calmette-Guerin infection. She was born to unrelated Argentinean parents, each of whom was heterozygous for this mutation. 561del4 has been previously described as a maternally inherited mutation in a compound heterozygous German patient. By single nucleotide polymorphism analysis of the areas surrounding the deletion, we showed the independent inheritance of 561del4 in three heterozygous carriers. Polypurine runs and "direct repeats," previously shown to be associated with areas of recurrent small deletions, were found in the flanking region of 561del4. The independent inheritance of three identical mutational events defines 561del4 as a new hotspot in the IFNGR1 gene.