Panel A shows a clinical timeline chart summarizing symptoms, treatments, diagnoses, and hematological parameter changes. Panel B shows histopathology micrographs demonstrating villous atrophy, inflammatory infiltrates, and immune-marker staining patterns. Panel C shows a pedigree diagram illustrating familial inheritance, carrier status, and affected homozygous offspring. Panel D shows Sanger sequencing chromatograms confirming the CTLA4 variant genotype in family members. Panel E shows a protein topology diagram highlighting transmembrane localization of the S172P variant. Panel F shows a three-dimensional protein model mapping evolutionary conservation around the affected residue. Panel G shows structural molecular models comparing wild-type and mutant proteins, revealing conformational perturbations.
Identification and structural characterization of the homozygous CTLA4 S172P/S172P variant associated with immune dysregulation. (A) Clinical timeline illustrating patient presentation, treatment interventions, and key laboratory findings. The colored shading represents the normal reference range for the respective parameter. (B) Histopathology of duodenal biopsy. (Panel a) Hematoxylin and eosin staining showing increased intraepithelial lymphocytes, mononuclear inflammatory cell infiltration in the lamina propria, irregular crypt architecture, and flattened/atrophic villi (20×), (Panel b) CD3 immunohistochemistry demonstrating dense T lymphocyte infiltration of the lamina propria and surface epithelium (20×), (Panel c) scattered and rare CD20-positive B lymphocytes in the lamina propria (20×), (Panel d) CD8 immunostaining highlighting cytotoxic T lymphocytes (20×), (Panel e) scattered and rare BCL6-positive B lymphocytes in the lamina propria (20×), (Panel f) PD-L1 immunostaining showing predominantly subsurface/near-luminal inflammatory cells, including lymphocytes and dendritic cells (20×). (C) Pedigree of the family showing inheritance pattern. (D) Sanger sequencing chromatograms of the proband, parents, and HC confirming the homozygous CTLA4: c.514T>C (p.S172P) variant. (E) Predicted structure of the CTLA-4 transmembrane domain obtained from the mCSM-membrane database, with the S172P mutant residue highlighted in red. (F) ConSurf-derived evolutionary conservation analysis mapped onto the AlphaFold-predicted CTLA-4 3D structure, indicating highly conserved residues in the vicinity of the S172P variant. (G) Structural comparison of WT and S172P mutant CTLA-4 generated in ChimeraX v1.10.1. Hydrogen bonds are colored light blue, hydrophobic contacts are purple, and steric clashes are depicted in pink, illustrating local conformational perturbations induced by the pathogenic variant. WT, wild-type; mut, mutant; PLT, platelet; Hb, hemoglabin; WBC, white blood cell; NEU, neutrophil; LYM, lymphocyte.