Case Report: The first Mainland Chinese case of

Cytotoxic T-lymphocyte-associated protein 4 (CTLA4) haploinsufficiency with autoimmune infiltration (CHAI) is an autosomal dominant condition featuring both immunodeficiency and autoimmunity. We describe the first published mainland Chinese patient harboring the heterozygous CTLA4 c.529dupT frameshift variant. While multiple CHAI cases have been documented in mainland China, this specific variant has not been reported in this population to date. The patient developed recurrent thrombocytopenia, recurrent respiratory infections and hypogammaglobulinemia at age 2. She was diagnosed with immune thrombocytopenia (ITP) at age 15. The disease subsequently progressed to Evans syndrome, alongside complications including chronic diarrhea, cerebral vasculitis, biliary tract infection and interstitial pneumonia. She received standard anti-infective therapy, combined glucocorticoids and immunosuppressants, as well as intravenous immunoglobulin (IVIG) replacement; however, these interventions yielded only limited and temporary benefits. After 38 years of disease progression, a primary immunodeficiency was suspected. Whole-exome sequencing (WES) verified the diagnosis of CHAI. Treatment with sirolimus led to amelioration of infection and diarrheal symptoms. This case exhibited phenotypic differences from prior patients carrying the identical variant. Our observations expand the known phenotypic spectrum of this variant and offer clinical references for the management and genetic testing of patients presenting with early-onset multisystem autoimmunity and immunodeficiency.