In November 2019, Coronavirus disease 2019 (COVID-19) caused by SARS-CoV-2 infection, which originated in Wuhan, China, quickly spread all over the world and became a pandemic. Almost two years have passed since then, and information on COVID-19 and kidney disease has been accumulating. In several cohort studies, including one from Japan, elevated serum creatinine levels at admission were a risk factor for aggravation of COVID-19, but it is not clear whether this elevated serum creatinine level was due to chronic kidney disease (CKD). Therefore, non-dialysis dependent CKD is uncertain whether it is the risk of aggravation of COVID-19. On the other hand, COVID-19 has become clear as a high-risk condition of acute kidney injury, and sufficient caution for it is required.

The classical roles of the complement (C) system are known to contribute in part to innate host immunity. In addition, bridging roles of the C system to adaptive immunity were found in the late 21st Century. Since anti-C agents such as C1-inhibitor and anti-C5 antibodies have started to be used in clinical practice during recent decades, the C system has become more familiar to clinicians. Analyses of aspects of the C system are now starting to clarify pathological mechanisms related to the C system and anti-C agents are under development. In the field of nephrology, unexpected C activation has been associated with the incidence, development and/or progression of glomerular and interstitial injuries. Moreover, atypical hematolytic uremic syndrome and C3 nephropathy were referred to as C-associated diseases. However, issues associated with C3 glomerulopathy, its pathogenesis, etiology and therapeutic approaches remain unclear. This mini-review provides a short summary and discussion of renal pathogeneses associated with the C system and its dysregulation, with particular focus on recent insights into C3 glomerulopathy.

The Japan Pediatric Society established an achievement goal as a board-certified pediatrician based on the skills in pediatric renal urology examination procedures such as abdominal ultrasonography and voiding cystourethrography (VCUG). A questionnaire-based survey was administered 61 young pediatricians with less than 10 years of experience in pediatrics. The questionnaire was based on whether pediatricians had acquired skills in abdominal ultrasonography for hydronephrosis and VCUG. It also enquired about knowledge on pediatric chronic kidney disease (CKD) apps and their practical uses. Among the 61 young pediatrician, 33 were board-certified pediatricians. Fifty-three (87%) pediatricians had acquired skills in abdominal ultrasonography for hydronephrosis and 40 (66%) pediatricians had acquired skills in VCUG. Forty-five (74%) and 57 (93%) pediatricians believed that an instruction manual is required to acquire skills in abdominal ultrasonography for hydronephrosis and VCUG, respectively. Fifth-one (84%) pediatricians had knowledge on pediatric CKD apps, although only 37 (61%) of them were practically using these apps. Many young pediatricians believe that an instruction manual is needed to acquire skills in VCUG. Young pediatricians are not familiar with pediatric CKD apps, thus, steady enlightenment activities are required.

Among children with spina bifida, more than 90% of cases with spina bifida aperta and approximately 40% with spina bifida occulta present with lower urinary tract dysfunction, which occasionally causes renal impairment. In this retrospective study, we aimed to investigate the clinical characteristics associated with renal impairment in children with spina bifida who were treated with clean intermittent catheterization and underwent ^99mTc-dimercaptosuccinic acid (DMSA) kidney scanning at our center. Renal impairment was defined as Group 2 or 3 using a classification based on DMSA scanning developed by Reflux Nephropathy Forum, Japan. Of the 62 patients enrolled, 15 (24%) were suffering from renal impairment. Spina bifida occulta was significantly associated with renal impairment and considered as a risk factor. Additionally, severe vesicoureteral reflux, hydronephrosis, and repeated febrile urinary tract infection were also significantly associated with renal impairment. Spina bifida occulta with lower urinary tract dysfunction was more frequently associated with renal impairment than spina bifida aperta. To prevent renal impairment, management of lower urinary tract function, including urinary state, is necessary while following up patients suffering from spina bifida with a high risk for renal impairment.

Atypical hemolytic uremic syndrome (aHUS) is characterized by thrombotic microangiopathy secondary to uncontrolled activation of the complement system. Extra-renal manifestations of aHUS affect the prognosis of this condition; therefore, optimal management of extra-renal manifestations of aHUS is important. A 3-year-old girl admitted with hematuria, proteinuria, and generalized edema was diagnosed with aHUS. We report a pediatric case of life-threatening extra-renal manifestations of aHUS, including gastrointestinal bleeding, refractory hypertension, pulmonary edema, and reversible cerebral atrophy in a patient who was successfully treated with multidisciplinary treatment. In addition to plasma exchange and eculizumab combination therapy, we administered renin-angiotensin system inhibitors for refractory hypertension and octreotide acetate for body fluid management in ischemic enteritis. Notably, multi-organ involvement in patients with extra-renal manifestations of aHUS can result in serious complications in the absence of appropriate treatment; therefore, systemic management with multidisciplinary treatment is important for improved prognosis.

High doses of steroid hormones are known to cause steroid-induced diabetes. Reports on the combination of idiopathic nephrotic syndrome (INS) and type 1 diabetes mellitus in children are rare. In this study, we experienced a 14-year-old boy with frequently relapsing nephrotic syndrome (FRNS) and slowly progressive insulin-dependent diabetes mellitus (SPIDDM). Steroid-induced diabetes developed during the 14th remission induction. Subsequently, urinalysis demonstrated positive glucose and HbA1c was 6.6%, despite the non-steroid treatment period. The oral glucose tolerance test (OGTT) and glucagon test showed impaired insulin secretion, which, together with positivity for anti-glutamic acid decarboxylase (GAD) antibody, led to the diagnosis of SPIDDM. Appropriate evaluation of glucose tolerance by HbA1c measurement is recommended at the time of induction of remission of nephrotic syndrome. In addition, it is important to measure autoantibodies, because there might be a correlation between the onset of steroid-induced diabetes and SPIDDM.