Our patient was originally referred to the Department of Rheumatology at the age of 24 year of age, with 6-year intermittent weakness of lower limbs and 4-year epilepsy period of attacks. In his childhood, he had mild developmental delay on language and sports, and had several fevers stemming from upper respiratory tract infections, requiring no hospital admission. At 18 years old, he suddenly felt the weakness of lower limbs during a run without any aura and loss of consciousness for the first time, with recovery after 10 minutes. The symptom relapsed 1-3 times every year and there was no movement disorder in the inter-ictal phase. At 20 years old, he began to suffer from epileptic seizures once each year. After his fourth seizure at 24-years of age, the symptoms became more noticeable. His weakness of lower limbs began to aggravate with longer-lasting (15-30 minutes) and more frequent attacks. Before being admitted to the hospital, he was suffering from uncontrolled seizures every day for nearly two weeks.
He was found to have mild neutropenia and thrombocytopenia for more than three years. Clinical evaluation of the patient was initially performed by a physician, and no specific noticeable body examinations were found, including normal myodynamia and muscular tension. Initial investigations revealed markedly elevated creatine kinase (1540U/L). Serology testing for antibodies to viruses were positive for an EBV IgG, and later viral DNA detection confirmed a high EBV-DNA load (7.93×106 copies/ml). An antinuclear antibodies profile and myositis-specific autoantibodies were negative. Electromyography (EMG) revealed myopathic changes that were most pronounced in both arms and legs. The PET-CT showed widespread adenopathy and skeletal muscle with avid fluorodeoxyglucose (FDG) uptake (Figure 1A a). Lower limbs MRI confirmed diffuse muscle inflammation (Figure 1A b&c). IVIG and a low dose of steroids were attempted to ameliorate the inflammation in muscles for less than a week, and creatine kinase descended to 385U/L (normal range). However, three months later, the patient began to suffer sustained muscle weakness and had a difficulty walking independently. After admission, ultrasound examination suggested generalized superficial lymphadenopathy. A muscle biopsy was performed to investigate histological changes. The pathology of muscle suggested that plenty of lymphocytes infiltrated into the endomysium. Histopathology staining revealed the infiltrated lymphocytes were stained with CD3, CD20, and EBER (Figure 1B). Bone marrow examination showed normal trilineage hematopoiesis. Considering the patient’s clinical and pathological manifestations, a targeted exome sequencing for immune deficiency was conducted.
Targeted exome sequencing using PBMC revealed that the patient was carrying a hemizygous loss-of-function mutation in the exon 8 of MAGT1: c.991C>T, p.Arg331*, while his mother was normal (Figure 1C). RT-PCR amplifying was performed in the PBMCs and muscles. Unsurprisingly, the MAGT1 expression was significantly decreased in the patient’s PBMCs, as well as in his muscles (Figure 1D). Sanger sequencing using the patient’s muscle revealed the same single base substitution (Figure 1E). Given the predominant susceptibility of the patient to EBV infection, the patient was then diagnosed as XMEN.
In-depth immunophenotype analysis of the patient
We determined the immunophenotype of the patient. Not surprisingly, the CD4/CD8 ratio decreased to 0.9. However, we found an increased intermediate expression of CD4 in T cells (CD4-int cells) (Figure 2A), while the T helper (Th) proportions, including Th1, Th2, Th9, Th17, Th17.1, Th22, follicle T helper (Tfh), and regulatory T (Treg) cells, were in the normal range (Table 1 and Supplementary Figure 1). Meanwhile, we noticed a decreased expression of CD127 in CD4+T cells (Figure 2B). Moreover, the NKG2D expression was much lower in our patient compared with healthy control both in CD8+CTLs and NK cells (Figure 2C).
TCR-induced Mg2+ influx in PBMCs was then measured as previously described. The patient’s Mg2+ influx induced by anti-CD3 in CD8+ cells was not detectable comparing to his mother. Similar results were shown in his CD4+T cells (Supplementary Figure 2).
The patient was then prescribed with oral Mg2+ supplementation and discharged. In the subsequent 2 months, the patient’s muscle weakness did not change but had fewer seizure attacks. The flow cytometry analysis revealed a decreased number of CD4-int (Figure 2A) and CD4+CD127-cells (Figure 2B). Nevertheless, the NKG2D expression remained unchanged both in CD8+CTLs and NK cells (Figure 2C).