PMC8721048_01
Histopathologic findings obtained by open surgery biopsy at age 8. (A) Hematoxylin and eosin (HE) staining showing diffuse lymphocytic infiltration involving the meninges (arrow), the vessels (asterisk) and the CNS tissue. (B) HE staining shows fibrinoid necrosis of the vessel walls with lymphocytic cell infiltrates. (C) Staining with a CD20 marker (brown) shows the distribution pattern of B-cells, primarily restricted to the meninges and the vessel walls. (D) Staining with a CD8 marker (brown) shows the distribution pattern of CD8+ T-cells with diffuse infiltration of the meninges, the vessel walls and the brain parenchyma. CD3+ T-cells showed a similar distribution pattern (data not shown). (E) Thrombotic occlusive vasculopathy (arrow) is shown. (F) CD34 staining of the vessel endothelia shows thin and fragmented endothelia (arrow) with partially thrombosed vessels, indicating severe vascular injury.
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Open cerebral biopsy showed extensive lymphomonocytic infiltration of the meninges and parenchyma as well as most perivascular regions with fibrinoid necrosis of the vessel walls and brain parenchyma ( Figure 1 ).
Cerebral magnetic resonance imaging (cMRI) of the index patient at age 10. (A, B) T1-weighted, contrast enhanced MRI scans in coronal (A) and axial (B) plane depicting the hypertrophic pachymeningitis with bilateral basal ganglia, midbrain and cortical lesions. Note the postinfectious internal hydrocephalus. (C) 3D reconstitution of the vascular system of the brain showing bilateral media aneurysms and a posterior cerebral artery aneurysm on the right without signs of vessel narrowing. (D) T2-weighted MRI scan in coronal plane highlighting the extensive frontotemporal white matter edema on the left, global parenchymal atrophy and the medial cerebral artery aneurysms bilaterally.
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A cMRI revealed a hypertrophic pachymeningitis with progression of the lesions bilaterally within the hemispheres of the brain with mild hemorrhage ( Figure 2 ).
Molecular and functional characterization of a novel SH2D1A mutation: (A) Family Pedigree. The arrow indicates the index patient. Mutation analysis confirmed a hemizygous SH2D1A mutation in patient II,8 and female carrier status in his mother I,2. One half-brother died at the age of 3 from acute leukaemia after suspected EBV infection (II,1), without confirmation of the XLP1 genotype by sequencing. No genetic analysis could be performed in other family members (indicated by question marks). (B) Results of Sanger sequencing of SH2D1A of the index patient, the mother and a healthy male individual are shown. Red column indicates position of the start codon mutation (ChrX:g.123480494 T>G; GRCh37/hg19). (C) Intracellular SAP expression due to novel SH2D1A mutation. Mean fluorescence intensities (MFI) representing intracellular SAP expression in CD56+ NK-cells, CD4+ T-cells, and CD8+ T-cells of one representative healthy control (blue), and the index patient (red) are shown in histograms (isotype control staining is shown in grey). Diagram of MFI representing SAP expressions of six healthy controls consisting of 3 male sex matched controls (shown as blue triangles) and 3 anonymous blood donors (shown as blue dots), the index patient (shown as red squares) and relating isotype control staining (shown as grey rings, triangles and squares) are shown in the right figure (lines represent geometric mean). (D) Quantification analysis of intracellular SH2D1A expression. MFI of intracellular SH2D1A expression in CD56+ NK-cells, CD3+CD4+ T-cells and CD3+CD8+ T-cells from five healthy controls including 3 male sex matched controls and 2 anonymous blood donors as well as the SH2D1A-deficient index patient following 3 days of PHA (phytohemagglutinin)-stimulation are shown (bars and top numbers represent mean values, error indicators represent standard deviations, staining of isotype controls are shown in black).
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The family pedigree of the patient is shown in  Figure 3A . SH2D1A gene (ChrX:g.123480494 T>G, NM_002351.5:c.2T>G, NP_002342.1:p.M1?, Exon 1) was revealed independently by targeted resequencing of genes associated with PID's and whole exome sequencing. Sequencing of the patient's mother confirmed maternal segregation of the variant ( Figure 3B ). T-cells and CD8+ T-cells of the patient as compared to those of six healthy controls (3 anonymous blood donors and 3 sex-matched controls) ( Figure 3C ). The findings indicate that the start codon mutation led to a drastic reduction but possibly not a complete absence of SH2D1A expression. T-cells of the patient seemed to be upregulated following PHA stimulation but was still drastically decreased compared to detected SAP levels in cells of healthy controls ( Figure 3D ). Therefore, the results indicate the reduced translational activity for SAP protein expression in the patient. The final diagnosis of XLP1 with EBV-negative CNS inflammation was established.