A Germline Heterozygous Dominant Negative IKZF2 Variant Causing Syndromic Primary Immune Regulatory Disorder and ICHAD.

Monogenic defects that impair the control of inflammation and tolerance lead to profound immune dysregulation, including autoimmunity and atopy. Studying these disorders reveals important molecular and cellular factors that regulate human immune homeostasis and identifies potential precision medicine targets. Here, we provide a detailed immunological assessment of a pediatric patient with a recently discovered syndrome causing Immunodysregulation, Craniofacial anomalies, Hearing impairment, Athelia, and Developmental delay (or ICHAD syndrome). The immunodysregulation resulted in autoimmune hemolytic anemia (AIHA) and atopic dermatitis. The patient carried a de novo germline heterozygous c.406+540_574+13477dup;p.Gly136_Ser191dup variant in IKAROS family zinc finger 2 (IKZF2), which encodes HELIOS. This variant led to reduced HELIOS protein expression and dominant interference of wild-type HELIOS-mediated repression of the IL2 promoter. Multi-parameter flow cytometry analyses of patient peripheral blood mononuclear cells revealed strongly impaired natural killer cell differentiation and function, and increased CD8⁺ T cell activation and cytokine secretion. Strikingly, patient CD4⁺ T cells were hyperactive, produced elevated levels of nearly all T helper (T_H) cytokines, and readily proliferated in response to stimulation. Patient regulatory T cells (Tregs) developed normally but aberrantly produced high levels of many T_H cytokines. Single-cell RNA sequencing revealed largely normal Tregs (albeit mostly memory), but naïve CD4⁺ T cells that were more enriched in genes related to activation, proliferation, metabolism, and T_H differentiation. This work describes the immunological phenotype of one of the first reported cases of germline dominant negative HELIOS deficiency, expands our understanding of the pathogenesis of AIHA on a single cell level, and provides valuable insights into HELIOS function in a variety of lymphocyte subsets.