Table 1 shows the general information of the patients. The 12 patients, including seven males and five females, were all from nonconsanguineous families. Eleven patients were diagnosed with STAT3 LOF mutations, and one patient (P12) was diagnosed with a STAT3 GOF mutation. Eleven STAT3-deficient patients were diagnosed at a median age of 4.74 years (0.5-12 years old), while the median age at symptom onset was 1.89 years (neonate-11.5 years old), with 5 infantile-onset patients (P1, P7, P8, P10 and P11). The age at symptom onset in STAT3 GOF mutation patient was 13 years. All the patients were full-term, with either cesarean section (2/12) or spontaneous (10/12) deliveries.
3.2 Infectious complications of 11 STAT3 LOF patients
All patients suffered from eczema, especially in the facial and scalp areas. More seriously, some eczema spread from the scalp to the limbs. Recurrent respiratory infections were the most common manifestation in our patients (11/11). Moreover, infections in other systems were also observed, such as otitis media in 5 (P1, P3, P4, P5 and P6), rhinitis in 1 (P10) and diarrhea in 2 (P7 and P8). Rotavirus was detected in P8. Staphylococcus aureus infection is one of the noteworthy characteristics of STAT3-deficient patients. Almost half of the patients (P2, P3, P4, P5, P7 and P9) had Staphylococcus aureus pneumonia that was confirmed by either sputum, blood, or bronchoalveolar lavage fluid (BALF) culture. Abscesses occurred in 8 patients in different body parts: lungs in 5 (P2, P3, P7, P9 and P10), the scalp in 4 (P2, P4, P7 and P10), the abdomen in 1 (P7) and the gluteal region in 1 (P1). Moreover, P7 and P10 underwent partial lung lobectomy. Approximately half of our patients (5/11. P3, P5, P6, P8 and P9) had marked chronic mucocutaneous candidiasis (CMC) verified by microscopic examination fungal cultures. Eight patients (8/11. P2, P4, P5, P6, P7, P9, P10 and P11) had a fever. (Figure 1).
EBV-DNA was measured in the PBMCs in 2 out of the 11 patients (P7 and P10), and the viral loads were 9.00E+03 and 2.60E+03, respectively. Cytomegalovirus (CMV)-DNA was also detected in blood, urine and BALF samples in two patients (P6 and P8) with viral loads of 8.69E+04 and 2.00E+05, respectively.
3.3 Immunological presentation in 11 STAT3 LOF mutation patients
The eosinophil count was elevated to different degrees (470~5860 cells/μL, reference range: 30–500 cells/μL). (Table 1). Elevated serum IgE is considered one of the most prominent characteristics in STAT3-deficient patients. Except for P8 (67.2 KU/L) and P11 (43.87 KU/L), the other patients had high serum IgE levels ranging from 1841.29 KU/L to 17310.4 KU/L (the average reference value range was <100 KU/L). The IgG, IgA and IgM levels remained approximately normal. (Table 2).
Lymphocytes remained approximately normal in our patients, although the absolute numbers of total T cells (in P1 and P4), CD4 T cells (in P4 and P7) and total B cells (in P5 and P7) were slightly elevated. Four patients (P3, P7, P9, P10) had reduced numbers of NK cells (Table 2). We analyzed the T cell and B lymphocyte subpopulations in three patients who underwent blood sampling. All of these patients presented with elevated levels of double-negative T cells and reduced levels of memory B cells. P8 had a two-fold higher than normal level of effector memory cytotoxic T cells, while P9 had a two-fold higher than normal level of terminally differentiated effector memory cytotoxic T cells. P4 had a dramatic reduction in γδ T cells (Table 3).
3.4 Nonimmunological abnormalities in 11 STAT3 LOF mutation patients
Two patients (2/11. P5 and P7) suffered from delayed growth. Retention of primary teeth also occurred in three patients (3/11. P1, P2 and P7). Three patients (3/11. P1, P5 and P7) developed the characteristic facial features. A broad nose and high-arched palate were observed in P1. Meanwhile, P5 and P7 had coarse facial skin and prominent foreheads. Scoliosis and pigeon breast occurred in only P7. P5 experienced a fracture of the collar bone. Cavernous hemangioma was observed in P9. Furthermore, lymphadenopathy of the neck and inguen was observed in 4 patients (P2, P4, P6 and P7). Splenomegaly was detected in P5 and P7, and the former also suffered from hepatomegaly. Furthermore, P5 and P10 exhibited food allergies (Figure 1).
As previously reported , the National Institutes of Health (NIH) scoring system is the most commonly used clinical scoring system for STAT3-deficient diseases. In our study, 9 out of 11 patients reached or exceeded 40 points, and two patients scored below the diagnostic standard (P8 and P11, with scores of 27 and 21, respectively). We noticed that the evaluation year of P8 and P11 was 0.5 years and 0.83 years, respectively.
3.5 STAT3 GOF mutation
P3 suffered from repeated cough, rhinitis, diarrhea and CMC. Diffusely enlarged lymph nodes and hepatosplenomegaly were observed in this patient. She also had autoimmune hemolytic anemia, reduced white blood cell and platelet counts, muscle weakness, diabetes, alopecia and delayed pubertal development. Her IgE level was 221.65 KU/L. The patient had severely reduced levels of all lymphocyte subsets. Her EBV-DNA viral load was 4.05E+04 in the PBMCs, and her mycoplasma viral load was 2.42E+08.
3.6 Mutation of the STAT3 gene
WES suggested that these patients had heterozygous mutations in STAT3. (Figure 2). As shown in Table 1, the variants were all de novo mutations except for the mutation in P11, who inherited the mutation from his father (c.994C>A; p.H332N). We noticed that c. 1144C>T (p.R382W) was the most common mutation in our study, which was identified in 3 patients (27.27%), followed by c. 1311C>A (p.H437Q) in 2 patients (18.18%). H437Q and R609T were two novel mutations that could not be found in the OMIM and ClinVar databases. Moreover, H437Q and R609T were predicted to be disease-causing mutations in MutationTaster; they were also predicted to be deleterious mutations by PopViz software  (Figure 3). Moreover, the GOF mutation was a known mutation (1261G>A; p.G421R) that was proven to be GOF by Milner .
All 11 STAT3 LOF mutation patients were given prophylactic antimicrobials and symptomatic treatment. Eight patients (P1, P2, P3, P4, P5, P6, P8 and P11) achieved a notable improvement in their eczema, respiratory infections and candida infections after receiving intravenous immunoglobulin (IVIG) at a dose of 400-600 mg/kg/m2. Four patients (P1, P2, P4 and P6) underwent immunoglobulin monitoring after IVIG. The level of IgG remained normal or slightly increased. The STAT3 GOF mutation patient received treatment with the anti-IL6R monoclonal antibody tocilizumab and achieved a stable condition with less alopecia, normal blood glucose levels and fewer infections.