An Adult Case of Chronic Mucocutaneous Candidiasis and Autoimmune Hepatitis Due to <i>STAT1</i> Gain-of-Function Variant

A 23-year-old woman presented with a history of recurrent oral and vaginal candidiasis and herpes zoster since childhood. In year X−1, she was diagnosed with autoimmune hepatitis (AIH) based on elevated liver enzymes, hypergammaglobulinemia, and histopathological findings of lymphocytic and plasmacytic infiltration in the portal tracts. Despite an initial response to high-dose glucocorticoids (GCs), the AIH relapsed during tapering. Immunological workup revealed impaired T cell proliferative capacity, undetectable T cell receptor excision circles (TREC) and kappa-deleting recombination excision circles (KREC), and a reduced proportion of Th17 cells. Genetic analysis identified a previously reported heterozygous STAT1-gain-of-function (GOF) variant (c.821G&amp;gt;A), establishing the diagnosis of symptomatic chronic mucocutaneous candidiasis (CMC) associated with STAT1-GOF. Given the increasing evidence for the efficacy of JAK inhibitors in STAT1-GOF, ruxolitinib therapy is planned in our patient following institutional ethical approval. The clinical severity of STAT1-GOF is highly variable among affected individuals. STAT1-GOF can present with a broad spectrum of autoimmune manifestations. While AIH has been reported in pediatric patients, adult-diagnosed cases remain relatively rare. Insufficient awareness of this entity in adult medicine may lead to significant diagnostic delays. In the present case, the diagnosis of STAT1-GOF was established based on a clinical history of recurrent candidiasis and herpes zoster since childhood, appearing alongside GC-dependent AIH. We believe that documenting the clinical course of adult-diagnosed cases is essential for improving the recognition of the diverse clinical spectrum of STAT1-GOF among physicians caring for adult patients.