Objective To investigate the incidence rate of infectious diseases during hospitalization in late preterm infants in Beijing, China, as well as the risk factors for infectious diseases and the effect of breastfeeding on the development of infectious diseases. Methods Related data were collected from the late preterm infants who were hospitalized in the neonatal wards of 25 hospitals in Beijing, China, from October 23, 2015 to October 30, 2017. According to the feeding pattern, they were divided into a breastfeeding group and a formula feeding group. The two groups were compared in terms of general status and incidence rate of infectious diseases. A multivariate logistic regression analysis was used to investigate the risk factors for infectious diseases. Results A total of 1 576 late preterm infants were enrolled, with 153 infants in the breastfeeding group and 1 423 in the formula feeding group. Of all infants, 484 (30.71%) experienced infectious diseases. The breastfeeding group had a significantly lower incidence rate of infectious diseases than the formula feeding group (22.88% vs 31.55%, P=0.033). The multivariate logistic regression analysis showed that breastfeeding was an independent protective factor against infectious diseases (OR=0.534, P=0.004), while male sex, premature rupture of membranes, gestational diabetes mellitus, and asphyxia were risk factors for infectious diseases (OR=1.328, 5.386, 1.535, and 2.353 respectively, P < 0.05). Conclusions Breastfeeding can significantly reduce the incidence of infectious diseases and is a protective factor against infectious diseases in late preterm infants. Breastfeeding should therefore be actively promoted for late preterm infants during hospitalization.

Objective To study the safety and efficacy of magnetic resonance imaging (MRI)-compatible incubator in cranial MRI examination for neonates. Methods A total of 120 neonates who were hospitalized in three hospitals and needed to undergo MRI examination were randomly divided into a control group and an experimental group, with 60 neonates in each group. The neonates in the experimental group were transferred with MRI-compatible incubator and underwent cranial MRI examination inside the MRI-compatible incubator, and those in the control group were transferred using a conventional neonatal transfer incubator and then underwent MRI examination outside the incubator. The two groups were compared in terms of the primary efficacy index (total examination time), secondary efficacy indices (times of examination, MRI completion rate on the first day of use), and safety indices (incidence rate of adverse events and vital signs). Results There were no significant differences in total examination time, times of examination, and MRI completion rate on the first day of use between the two groups (P > 0.05). There were also no significant differences between the two groups in the incidence rate of adverse events and vital signs such as respiratory rate, heart rate, blood pressure, and blood oxygen saturation rate at different time points before and after examination (P > 0.05). Conclusions The use of MRI-compatible incubator does not significantly shorten the examination time of cranial MRI, but it does provide a relatively stable environment for examination with acceptable safety. There is a need for further studies with a larger population.

Objective To study the association of fatty acid composition in human milk with breast milk jaundice (BMJ) in neonates. Methods A total of 30 full-term neonates who were admitted to the neonatal intensive care unit from October 2016 to October 2017 and were diagnosed with late-onset BMJ were enrolled as the BMJ group. Thirty healthy neonates without jaundice or pathological jaundice who were admitted to the confinement center during the same period of time were enrolled as the control group. Related clinical data were collected, including sex, mode of birth, feeding pattern, gestational age, birth weight, gravida, parity, and peak level of total serum bilirubin. Breast milk was collected from the mothers, and the MIRIS human milk analyzer was used to measure macronutrients (fat, protein, and carbohydrate) and calorie. Gas chromatography was used to analyze the content of different fatty acids in breast milk. Results The control group had higher levels of macronutrients in human milk than the BMJ group, with significant differences in fat, dry matter, and calorie (P<0.05). In addition, 25 fatty acids were detected in breast milk, including 9 saturated fatty acids, 6 monounsaturated fatty acids, and 10 polyunsaturated fatty acids. The comparison of the percentage composition of different fatty acids showed that compared with the control group, the BMJ group had significantly lower percentage compositions of C15:0, C16:0, C17:0, C18:0, C20:0, C18:1n9t, C20:1n9, C18:3n6, C22:2, and C22:6n3 (DHA) and higher percentage compositions of C10:0, C12:0, C14:0 in breast milk (P<0.05). Conclusions Some macronutrients and fatty acid composition in human milk may be associated with the pathogenesis of BMJ in neonates.

Objective To study the application value of whole exome sequencing (WES) in critically ill neonates with inherited diseases. Methods A total of 66 critically ill neonates with suspected inherited diseases or unclear clinical diagnosis who were admitted to the neonatal intensive care unit were enrolled as subjects. The clinical data of the neonates were collected, and venous blood samples were collected from the neonates and their parents for WES. The clinical manifestations of the neonates were observed to search for related pathogenic gene mutations. Results Among the 66 critically ill neonates with suspected inherited diseases or unclear clinical diagnosis (34 boys and 32 girls), 14 (21%) were found to have gene mutations by WES. One neonate had no gene mutation detected by WES but was highly suspected of pigment incontinence based on clinical manifestations, and multiplex ligation-dependent probe amplification detected a heterozygous deletion mutation in exons 4-10 of the IKBKG gene. Among the 15 neonates with gene mutations, 10 (67%) had pathogenic gene mutation, 1 (7%) was suspected of pathogenic gene mutation, and 4 (27%) had gene mutations with unknown significance. Among the 15 neonates, 13 underwent chromosome examination, and only 1 neonate was found to have chromosome abnormality. Conclusions Chromosome examination cannot be used as a diagnostic method for inherited diseases, and WES detection technology is an important tool to find inherited diseases in critically ill neonates with suspected inherited diseases or unclear clinical diagnosis; however WES technology has some limitation and it is thus necessary to combine with other sequencing methods to achieve an early diagnosis.

Objective To investigate the epidemiology, clinical features, treatment, and prognostic factors of neonatal acute respiratory distress syndrome (NARDS) through a retrospective study of NARDS based on the Montreux definition. Methods A retrospective analysis was performed on the medical records of neonates who were hospitalized from January 2017 and July 2018, among whom 314 neonates who met the Montreux definition were enrolled as subjects. According to oxygen index, they were divided into a mild NARDS group with 130 neonates, a moderate NARDS group with 117 neonates, and a severe NARDS group with 67 neonates. The clinical features were compared among the three groups to investigate the influencing factors for the severities of NARDS and the length of hospital stay. Results The neonates with NARDS accounted for 2.46% (314/12 789) of the neonates admitted to the neonatal ward during the same period of time and had a mortality rate of 9.6% (30/314). The multivariate ordinal logistic regression analysis showed that the neonates who used pulmonary surfactant (PS) or had a long duration of assisted ventilation tended to have a higher risk of severe NARDS (P < 0.05). The Cox regression analysis showed that the neonates with low birth weight/macrosomia, preterm birth, invasive ventilation, PS therapy, or positive pathogenic detection had a higher risk of prolonged hospital stay (P < 0.05). Conclusions Preterm birth, low birth weight/macrosomia, and perinatal infection may be associated with an increased risk of severe NARDS. The neonates requiring invasive ventilation, prolonged assisted ventilation, or PS therapy tend to have a poor prognosis.

Objective To study the application of ponderal index (PI), body mass index (BMI), mid-arm circumference/head circumference (MAC/HC), and Clinical Assessment of Nutritional Status (CANS) score in assessing the nutritional status of neonates at birth, and to find a simple and reliable scheme for the assessment of fetal nutritional status. Methods PI, BMI, MAC/HC, and CANS were used to assess the nutritional status of full-term infants and preterm infants shortly after birth. The assessment results of these methods were analyzed. Results Among the 678 full-term infants, 61, 102, 47, and 131 were diagnosed with malnutrition by PI, BMI, MAC/HC, and CANS respectively. Among the 140 preterm infants, 30, 87, 9, and 112 were diagnosed with malnutrition by PI, BMI, MAC/HC, and CANS respectively. The combination of BMI and CANS had a detection rate of 99.3% in full-term infants and 100% in preterm infants. Compared with the single method, the combination significantly improved the detection rate of malnutrition (P < 0.05), while there was no significant difference between the combination of BMI+CANS and the combination of PI+BMI+CANS (P > 0.05). Conclusions The combination of BMI+CANS can reduce the rate of missed diagnosis of fetal malnutrition. It is therefore a simple and reliable method for the assessment of fetal malnutrition.

Objective To study the clinical significance of minimal residual disease (MRD) in B-lineage acute lymphoblastic leukemia (B-ALL) pediatric patients with different fusion gene backgrounds. Methods A retrospective analysis was performed on the medical data of 441 B-ALL children who were treated from January 2008 to April 2015. Among the 441 children, 336 had negative fusion gene, 79 had positive ETV6-RUNX1 fusion gene, and 26 had positive E2A-PBX1 fusion gene. Flow cytometry was used to detect MRD, and the influence of MRD on day 15 (TP1), day 33 (TP2), and week 12 (TP3) of induction therapy on prognosis was analyzed. Results In patients with negative fusion gene, the positive MRD group had significantly lower overall survival (OS) rate and event-free survival (EFS) rate (P < 0.05) and significantly higher recurrence rate and mortality rate at TP1, TP2, and TP3, compared with the negative MRD group (P < 0.05). In patients with positive ETV6-RUNX1, the positive MRD group had significantly lower OS and EFS rates (P < 0.05) and significantly higher recurrence rate and mortality rate (P < 0.05) than the negative MRD group only at TP1. In patients with positive E2A-PBX1, there were no significant differences in the OS rate, recurrence rate, and mortality rate between the positive and negative MRD groups at TP1, TP2, and TP3 (P > 0.05). Conclusions MRD has the most definite prognostic significance in pediatric B-ALL patients with negative fusion gene, while it has unsatisfactory prognostic significance in those with positive ETV6-RUNX1 or positive E2A-PBX1.

Objective To explore the clinical-biological characteristics and prognosis of pediatric pro-B cell acute lymphoblastic leukemia (pro-B-ALL). Methods A total of 64 patients aged less than 18 years old with pro-BALL were enrolled. Clinical characteristics, therapeutic effect and prognostic factors were retrospectively analyzed. Results Pro-B-ALL occurred in 6.23% (64/1 028) of pediatric ALL. Among the 64 patients, 35 were male and 29 were female. The median age was 7.0 years (range 0.4-16.0 years) at diagnosis, of which 39% and 6% were ≥ 10 years old and < 1 year old respectively. The median WBC count was 25.5×10⁹/L[range (0.4-831.9)×10⁹/L], of which 35.9% were ≥ 50×10⁹/L. MLL-r positivity was the most frequent genetic alteration in pro-B ALL, occurring in 34% of patients, with lower frequency of CD22 and CD13 expression and higher frequency of CD7 expression, while lower frequency of CD33 expression was found in patients with MLL-AF4 positivity. At a median follow-up of 60.0 months (range 4.9-165.3 months), the estimated 5-year overall survival (OS) and event-free survival (EFS) in the 64 patients were (85±5)% and (78±5)% respectively. Cox proportional hazards regression analysis identified MRD ≥ 0.1% at 3 months after chemotherapy as an independent adverse prognostic factor for both 5-year OS and EFS. Conclusions Pediatric pro-B ALL is a heterogeneous disease with clinical and biological diversity. Biological characteristics, such as immunological markers, genetic alterations, and MRD at 3 months after chemotherapy may be important factors for the long-term prognosis.

Objective To study the changes in metabolic markers and clinical outcome after treatment with different drug regimens in children with bipolar affective disorder. Methods A retrospective analysis was performed on the medical data of 220 children with bipolar affective disorder who attended the hospital from January 2017 to January 2020. According to the treatment method, 112 children treated with atypical antipsychotic drugs alone were enrolled as the control group, and 108 children treated with atypical antipsychotic drugs combined with mood stabilizer were enrolled as the study group. The two groups were compared in terms of baseline data, changes in related metabolic markers[fasting insulin (FIN), glycosylated hemoglobin (HbAlc), total cholesterol (TC), triglyceride (TG), high-density lipoprotein cholesterol (HDL-C), and low-density lipoprotein cholesterol (LDL-C)] after treatment, incidence rate of metabolic syndrome, and clinical outcome. Results There were no significant differences in the baseline data including age, sex, and course of disease between the two groups (P > 0.05). The study group had a significantly higher overall response than the control group (92.6% vs 82.1%, P < 0.05). Before treatment, there were no significant differences in the levels of FIN and HbAlc between the two groups (P > 0.05). After treatment, the control group had a significant increase in the level of FIN and a significantly higher level of FIN than the study group (P < 0.05). The study group showed no significant change in the level of FIN after treatment (P > 0.05). There was no significant difference in the level of HbAlc between the two groups before and after treatment (P > 0.05). Before treatment, there were no significant differences in the levels of TC, TG, HDL-C, and LDL-C between the two groups (P > 0.05), and after treatment, the control group had significant increases in TC and TG and significantly higher levels of TC and TG than the study group (P < 0.05). The study group showed no significant changes in TC and TG after treatment (P > 0.05). There were no significant differences in the levels of HDL-C and LDL-C between the two groups before and after treatment (P > 0.05). The study group had a significantly lower incidence rate of metabolic syndrome than the control group (2.8% vs 9.8%, P < 0.05). Conclusions Atypical antipsychotic drugs combined with mood stabilizer in the treatment of bipolar disorder in children have little effect on the level of metabolic markers, and the curative effect is significant.

Objective To study the clinical features of Mycobacterium tuberculosis infection in children with secondary immunodeficiency disease (SID) versus primary immunodeficiency disease (PID). Methods A retrospective analysis was performed on the medical data of children with immunodeficiency and Mycobacterium tuberculosis infection (36 children with SID and 52 with PID) and 108 children with Mycobacterium tuberculosis infection but without immunodeficiency (control group). Results The onset age in the PID group was significantly lower than those in the control and SID groups (P < 0.05), and the proportation of males in the PID group was significantly higher than those in the control and SID groups (P < 0.05). Compared with the control group, the SID and PID groups had significantly lower incidence rates of tuberculosis poisoning symptoms (night sweeting, weight loss, fatigue and loss of appetite) and positive rate of PPD test (P < 0.05), as well as a significantly higher incidence rate of the involvement of ≥ 3 pulmonary lobes (P < 0.05). The children with PID tended to have the involvement of multiple organs (P < 0.05). The SID group had a significantly higher incidence rate of miliary shadow on chest CT than the control and PID groups (P < 0.05). The PID group had a significantly lower positive rate of IFN-gamma release assay (IGRA) than the control and SID groups (P < 0.05). Mycobacterium tuberculosis infection manifested as latent tuberculosis infection (36.1%) and active tuberculosis (63.9%) in the SID group. The infection mainly manifested as bacille Calmette-Guérin disease in the PID group (90.4%), among whom 2 children (3.8%) also had tuberculosis. Conclusions Children with immunodeficiency and Mycobacterium tuberculosis infection have atypical clinical symptoms, with a high incidence rate of disseminated infection and low positive rates of PPD and IGRA tests, which may lead to misdiagnosis and missed diagnosis. Children with immunodeficiency should undergo regular tuberculosis screening for early identification and intervention.

Objective To study the clinical features of children with recurrent Kawasaki disease (KD). Methods PubMed, Web of Science, Embase, CNKI, Wanfang Med Online, and Weipu Data were searched for case-control studies on the clinical features of initial and recurrent KD. The articles were screened according to the inclusion and exclusion criteria. RevMan 5.3 software was used to perform the Meta analysis. Effect models were selected based on the results of heterogeneity test, and then pooled OR or weighted mean difference (WMD), and their 95% CI were calculated. Results A total of 9 case-control studies were included, with 12 059 children with KD in total, among whom 206 children had recurrent KD (127 boys/61.7%; 79 girls/38.3%). The results of the Meta analysis showed that compared with the initial KD onset, the children with recurrent KD had a shorter duration of fever (WMD=-1.81, 95%CI:-2.99 to -0.64) and a lower proportion of children with swelling of the hands and feet (OR=0.46, 95%CI:0.26 to 0.80). There was no significant difference in the incidence rate of coronary artery lesions between recurrent KD and initial KD (OR=1.34, 95%CI:0.84 to 2.14). Conclusions Current evidence shows that children with recurrent KD tend to have a shorter duration of fever and a lower incidence of swelling of the hands and feet. KD recurrence is more common in boys. Current evidence does not show an increased risk of developing coronary artery lesions in children with recurrent KD.

Objective To study the percentage of the measured values of the main pulmonary ventilation function parameters in their predicted values based on Zapletal equation among healthy children aged 5-14 years in Kunming, China, and to provide a basis for accurate judgment of pulmonary ventilation function in clinical practice. Methods A total of 702 healthy children aged 5-14 years (352 boys and 350 girls) from Kunming were enrolled. The Jaeger spirometer was used to measure the nine indices:forced vital capacity (FVC), forced expiratory volume in one second (FEV1), ratio of forced expiratory volume in one second to forced vital capacity (FEV1/FVC), maximal mid-expiratory flow (MMEF), forced expiratory flow at 25% of forced vital capacity (FEF25), forced expiratory flow at 50% of forced vital capacity (FEF50), forced expiratory flow at 75% of forced vital capacity (FEF75), peak expiratory flow (PEF), and maximal voluntary ventilation (MVV). The values obtained from the Zapletal equation of predicted values provided by the spirometer were used as the predicted values of children, and the percentage of measured values in predicted values was calculated. Results In the 702 children, the percentages of the measured values of the main pulmonary ventilation function parameters PEF, FVC, FEV1, FEV1/FVC, and MVV in their predicted values fluctuated from 102% to 114%, 94% to 108%, 98% to 113%, 98% to 107%, and 141% to 183% respectively. As for the main airway velocity parameters, the percentages of the measured values of FEF25, FEF50, FEF75, and MMEF in their predicted values fluctuated from 98% to 116%, 85% to 102%, 71% to 98%, and 83% to 100% respectively. The percentages of the measured values of PEF, FVC, FEV1, FEV1/FVC, MVV, FEF25, FEF50, FEF75, and MMEF in their predicted values had the lower limits of normal of 88.2%, 88.4%, 92.0%, 94.4%, 118.5%, 82.9%, 70.0%, 62.1%, and 70.1% respectively. Conclusions There are differences between pulmonary ventilation function parameter levels and normal values provided by Zapletal equation in healthy children aged 5-14 years in Kunming. As for the pulmonary ventilation function parameters of PEF, FVC, FEV, FEV1/FVC, MVV, FEF25, FEF50, FEF75, and MMEF in these children, the lower limits of normal of measured values in predicted values may be determined as 88.2%, 88.4%, 92.0%, 94.4%, 118.5%, 82.9%, 70.0%, 62.1%, and 70.1% respectively.

A boy, aged 2 years and 4 months, had a sudden onset of blepharoptosis of the right eyelid, accompanied by the mouth deviated to the right side, drinking cough, nystagmus, and developmental regression. Cranial MRI showed softening lesions formed after infarction of the right dorsolateral medulla oblongata, while head CT angiography showed no imaging of the proximal part of the V4 segment of the right vertebral artery. The child was diagnosed with dorsolateral medulla oblongata syndrome and was treated with gamma globulin to regulate immune function, with mannitol to reduce neuronal edema, with low-molecular-weight heparin sodium to improve local hypercoagulation of occluded blood vessels, with hyperbaric oxygen to improve local ischemia and hypoxia and promote the recovery of brain function, and with neuromuscular electrical stimulation to promote the recovery of neuromuscular function. Before discharge, only mild right ataxia and Horner syndrome remained. This article reports the first case of infantile dorsolateral medulla oblongata syndrome and provides experience for the diagnosis and treatment of the disease.

A boy, aged 6 years and 11 months, was admitted due to nephrotic syndrome for 2 years, cough for 1 month, and shortness of breath for 15 days. The boy had a history of treatment with hormone and immunosuppressant. Chest CT after the onset of cough and shortness of breath showed diffuse ground-glass opacities in both lungs. Serum (1,3)-beta-D glucan was tested positive, and the nucleic acid of cytomegalovirus was detected in respiratory secretions. After the anti-fungal and anti-viral treatment, the child improved temporarily but worsened again within a short period of time. Pneumocystis jirovecii was identified by Gomori's methenamine silver staining in bronchoalveolar lavage fluid. The child was diagnosed with severe pneumonia (Pneumocystis jirovecii and cytomegalovirus infection), acute respiratory distress syndrome, and nephrotic syndrome. After anti-infective therapy with sulfamethoxazole/trimethoprim and ganciclovir and respiratory support, the child still experienced progressive aggravation of dyspnea and tension pneumothorax, and extracorporeal membrane oxygenation (ECMO) was given on day 13 of invasive ventilation. Anti-infective therapy with sulfamethoxazole/trimethoprim, ganciclovir, and linezolid, anticoagulation therapy, sedation therapy, nutrition, and comprehensive management of the respiratory tract were given during ECMO. The child was successfully weaned from ECMO after 72 days, resulting in a length of hospital stay of 134 days. The child was followed up for 6 months after discharge, and there was a significant improvement on lung CT, without organ dysfunction. It is concluded that Pneumocystis jirovecii pneumonia is a potential lifethreatening infection for children with low immunity, and that ECMO can effectively improve the prognosis of children with severe respiratory distress syndrome.

Objective To study the expression and significance of ubiquitin-specific protease 7 (USP7) and the key factors of the Wnt signaling pathway in the lung tissue of preterm rats after hyperoxia exposure. Methods A total of 180 preterm neonatal Wistar rats were randomly divided into an air control group, an air intervention group, a hyperoxia control group, and a hyperoxia intervention group, with 45 rats in each group. Lung injury was induced by hyperoxia exposure in the hyperoxia groups. The preterm rats in the intervention groups were given intraperitoneal injection of the USP7 specific inhibitor P5091 (5 mg/kg) every day. The animals were sacrificed on days 3, 5, and 9 of the experiment to collect lung tissue specimens. Hematoxylin-eosin staining was used to observe the pathological changes of lung tissue. RT-PCR and Western blot were used to measure the mRNA and protein expression levels of USP7 and the key factors of the Wnt signaling pathway β-catenin and α-smooth muscle actin (α-SMA) in lung tissue. Results The air groups had normal morphology and structure of lung tissue; on days 3 and 5, the hyperoxia control group showed obvious alveolar compression and disordered structure, with obvious inflammatory cells, erythrocyte diapedesis, and interstitial edema. On day 9, the hyperoxia control group showed alveolar structural disorder and obvious thickening of the alveolar septa. Compared with the hyperoxia control group at the corresponding time points, the hyperoxia intervention group had significantly alleviated disordered structure, inflammatory cell infiltration, and bleeding in lung tissue. At each time point, the hyperoxia groups had a significantly lower radial alveolar count (RAC) than the corresponding air groups (P < 0.05), and the hyperoxia intervention group had a significantly higher RAC than the hyperoxia control group (P < 0.05). On days 3, 5, and 9 of the experiment, the hyperoxia groups had significantly higher mRNA expression of USP7 and β-catenin and protein expression of USP7, β-catenin, and α-SMA than the corresponding air groups (P < 0.05). Compared with the hyperoxia control group, the hyperoxia intervention group had significant reductions in the mRNA expression of β-catenin and the protein expression of β-catenin and α-SMA (P < 0.05), while there were no significant differences in the mRNA and protein expression of USP7 between the hyperoxia intervention and hyperoxia control groups (P > 0.05). There were no significant differences in the mRNA expression of USP7 and β-catenin and the protein expression of USP7, β-catenin, and α-SMA between the air intervention and air control groups (P > 0.05). Conclusions Hyperoxia exposure can activate the Wnt/β-catenin signaling pathway, and USP7 may participate in hyperoxic lung injury through the Wnt/β-catenin signaling pathway. The USP7 specific inhibitor P5091 may accelerate the degradation of β-catenin by enhancing its ubiquitination, reduce lung epithelial-mesenchymal transition, and thus exert a certain protective effect against hyperoxic lung injury.

Extrahepatic biliary tract tumors are rare and among them rhabdomyosarcoma is most common. Rhabdomyosarcoma is a soft tissue malignant musculoskeletal tumor and is a very rare malignancy of the common bile duct in children. It usually presents as obstructive jaundice and/or pruritus. If there is no local invasion to the adjacent tissues, the radiological appearance of the tumor lesion is like a choledochal cyst. So the diagnosis is usually made at surgery or by preoperative biopsy. It is important to diagnose early and differentiate it from choledochal cyst and start treatment as early as possible for long time survival of the patient. This case report presented a case of a 10-year-old boy with recurrent onset of obstructive jaundice and fever preoperatively who was diagnosed as choledochal cyst and postoperatively as embryonal rhabdomyosarcoma of the common bile duct. After surgical resection and postoperative chemotherapy, the child had a good prognosis. So it is crucial to know that this rare tumor can mimic congenital choledochal cyst and it should be considered in the differential diagnosis of obstructive jaundice in children.

With the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) all over the world, there is an increasing number of children with such infection. Angiotensin-converting enzyme 2 (ACE2), one of the binding sites for SARS-CoV-2 infection in humans, can bind to viral spike proteins, allowing transmembrane serine protease (TMPRSS2) to activate S-protein to trigger infection and induce the production of various inflammatory factors such as interleukin-1, interferon-l, and tumor necrosis factor. Compared with adults, children tend to have lower expression levels of ACE2 and TMPRSS2, which are presumed to be associated with milder symptoms and fewer cases in children. The article summarizes the research advances in the role of ACE2 during SARS-CoV-2 infection, in order to help understand the pathogenic mechanism of SARS-CoV-2 and provide a reference for better development of drugs and vaccines to prevent and treat coronavirus disease 2019 in children.