CARD9 Deficiency Mimicking Hyper-IgE Syndrome

Caspase recruitment domain-containing protein 9 (CARD9) deficiency is a rare primary immunodeficiency characterized by a profound susceptibility to invasive fungal infections. Given its significant phenotypic overlap with hyper-IgE syndrome (HIES)—most notably, markedly elevated serum IgE levels—misdiagnosis remains a perilous clinical pitfall. We present 2 siblings from a consanguineous family harboring a rare homozygous nonsense mutation ( c.32G>A, p.Trp11* ) in the CARD9 gene, both presenting with severe invasive candidiasis. Case 1 developed vertebral osteomyelitis and central nervous system abscesses, while case 2 presented with fungal arthritis. Alarmingly, case 2 was misdiagnosed with juvenile idiopathic arthritis and erroneously treated with potent immunosuppressants, risking a catastrophic exacerbation of the fungal pathology. Following molecular confirmation, both were scheduled for curative hematopoietic stem cell transplantation. This report underscores the imperative of considering CARD9 deficiency in HIES-like presentations to avert detrimental immunosuppressive interventions.