Yoshitsugu Kaku

Clinicopathologic Correlation and Outcome of C1q Nephropathy

BACKGROUND AND OBJECTIVES The number of patients with C1q nephropathy (C1qN) in previous reports is small and the duration of follow-up is short. Our study describes the clinicopathologic correlation and clinical outcome through the mean follow-up period of 7.2 yr in 61 patients. DESIGN, SETTINGS, PARTICIPANTS, & MEASUREMENTS Sixty-one patients, 1 to 67 yr of age, with C1qN were enrolled in this study. RESULTS According to presentation at onset, patients were divided into two groups: asymptomatic urinary abnormalities (asymptomatic) (n = 36) and nephrotic syndrome (NS) (n = 25). Light microscopy showed minimal change disease (MCD) in 46 patients (75%), mesangial proliferative glomerulonephritis in 7 (12%), and focal segmental glomerulosclerosis (FSGS) in 8 (13%). The prevalence of MCD was higher in the NS group than in the asymptomatic group. Nine patients in the asymptomatic group and all patients in the NS group were treated with prednisolone and/or cyclosporine. Normal urinalysis was found in 10 patients in asymptomatic group and 8 in NS group during the follow-up. Thirteen patients in the NS group were frequent relapsers at the latest follow-up. Three patients with FSGS developed chronic renal failure 8 to 15 yr after the diagnosis. C1q deposits disappeared in 3 of 8 patients receiving repeat biopsy, and 2 of these 3 showed FSGS. CONCLUSIONS The prognosis of C1qN is good, associated with MCD in a large number. In some patients, C1q deposits disappear through the follow-up period. FSGS may develop in some patients on repeat biopsies. Further investigation is critically needed to settle this issue.

Clinical practice guideline for pediatric idiopathic nephrotic syndrome 2013: general therapy

Nephrotic syndrome is a disorder characterized by severe proteinuria, hypoproteinemia, and generalized edema resulting from damage to the glomerular basement membrane. In Western countries, nephrotic syndrome affects 2 of 100,000 children per year [1]. In Japan, approximately 1,300 new cases per year of pediatric nephrotic syndrome are reported to the Medical Aid for Specific Chronic Disease of Children and the disease develops in 5 of 100,000 children per year. Approximately 90 % of the cases of pediatric nephrotic syndrome are idiopathic, or of unknown cause. The first-line treatment for an initial episode of pediatric idiopathic nephrotic syndrome is oral steroid therapy, which leads to remission in approximately 80 % of cases (steroidsensitive nephrotic syndrome) [2]. However, 80 % of children with steroid-sensitive nephrotic syndrome experience one or more relapses, [3] and 50 % of these children have frequent relapses [4]. Those with frequently relapsing nephrotic syndrome are prone to suffer steroid-induced side effects such as obesity, growth impairment, hypertension, diabetes mellitus, osteoporosis, and adrenal insufficiency. Many cases of steroid-resistant nephrotic syndrome, where steroids are ineffective, progress to renal failure. Pediatric idiopathic nephrotic syndrome is a very important disease in the field of pediatric nephrology. The Scientific Committee in the Japanese Society for Pediatric Nephrology previously published the ‘‘Clinical Practice Guideline for Pediatric Idiopathic Nephrotic Syndrome’’ (2013). This is the English translation from the ‘‘Medical Therapy’’ portion of the guideline.Nephrotic syndrome is a disorder characterized by severe proteinuria, hypoproteinemia, and generalized edema resulting from damage to the glomerular basement membrane. In Western countries, nephrotic syndrome affects 2 of 100,000 children per year [1]. In Japan, approximately 1,300 new cases per year of pediatric nephrotic syndrome are reported to the Medical Aid for Specific Chronic Disease of Children and the disease develops in 5 of 100,000 children per year. Approximately 90 % of the cases of pediatric nephrotic syndrome are idiopathic, or of unknown cause. The first-line treatment for an initial episode of pediatric idiopathic nephrotic syndrome is oral steroid therapy, which leads to remission in approximately 80 % of cases (steroidsensitive nephrotic syndrome) [2]. However, 80 % of children with steroid-sensitive nephrotic syndrome experience one or more relapses, [3] and 50 % of these children have frequent relapses [4]. Those with frequently relapsing nephrotic syndrome are prone to suffer steroid-induced side effects such as obesity, growth impairment, hypertension, diabetes mellitus, osteoporosis, and adrenal insufficiency. Many cases of steroid-resistant nephrotic syndrome, where steroids are ineffective, progress to renal failure. Pediatric idiopathic nephrotic syndrome is a very important disease in the field of pediatric nephrology. The Scientific Committee in the Japanese Society for Pediatric Nephrology previously published the ‘‘Clinical Practice Guideline for Pediatric Idiopathic Nephrotic Syndrome’’ (2013). This is the English translation from the ‘‘Medical Therapy’’ portion of the guideline.

X-Linked Alport Syndrome Caused by Splicing Mutations in COL4A5

BACKGROUND AND OBJECTIVES X-linked Alport syndrome is caused by mutations in the COL4A5 gene. Although many COL4A5 mutations have been detected, the mutation detection rate has been unsatisfactory. Some men with X-linked Alport syndrome show a relatively mild phenotype, but molecular basis investigations have rarely been conducted to clarify the underlying mechanism. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS In total, 152 patients with X-linked Alport syndrome who were suspected of having Alport syndrome through clinical and pathologic investigations and referred to the hospital for mutational analysis between January of 2006 and January of 2013 were genetically diagnosed. Among those patients, 22 patients had suspected splice site mutations. Transcripts are routinely examined when suspected splice site mutations for abnormal transcripts are detected; 11 of them showed expected exon skipping, but others showed aberrant splicing patterns. The mutation detection strategy had two steps: (1) genomic DNA analysis using PCR and direct sequencing and (2) mRNA analysis using RT-PCR to detect RNA processing abnormalities. RESULTS Six splicing consensus site mutations resulting in aberrant splicing patterns, one exonic mutation leading to exon skipping, and four deep intronic mutations producing cryptic splice site activation were identified. Interestingly, one case produced a cryptic splice site with a single nucleotide substitution in the deep intron that led to intronic exonization containing a stop codon; however, the patient showed a clearly milder phenotype for X-linked Alport syndrome in men with a truncating mutation. mRNA extracted from the kidney showed both normal and abnormal transcripts, with the normal transcript resulting in the milder phenotype. This novel mechanism leads to mild clinical characteristics. CONCLUSIONS This report highlights the importance of analyzing transcripts to enhance the mutation detection rate and provides insight into genotype-phenotype correlations. This approach can clarify the cause of atypically mild phenotypes in X-linked Alport syndrome.

A pure chloride channel mutant of CLC-5 causes Dent’s disease via insufficient V-ATPase activation

Dent’s disease is characterized by defective endocytosis in renal proximal tubules (PTs) and caused by mutations in the 2Cl−/H+ exchanger, CLC-5. However, the pathological role of endosomal acidification in endocytosis has recently come into question. To clarify the mechanism of pathogenesis for Dent’s disease, we examined the effects of a novel gating glutamate mutation, E211Q, on CLC-5 functions and endosomal acidification. In Xenopus oocytes, wild-type (WT) CLC-5 showed outward-rectifying currents that were inhibited by extracellular acidosis, but E211Q and an artificial pure Cl− channel mutant, E211A, showed linear currents that were insensitive to extracellular acidosis. Moreover, depolarizing pulse trains induced a robust reduction in the surface pH of oocytes expressing WT CLC-5 but not E211Q or E211A, indicating that the E211Q mutant functions as a pure Cl− channel similar to E211A. In HEK293 cells, E211A and E211Q stimulated endosomal acidification and hypotonicity-inducible vacuolar-type H+-ATPase (V-ATPase) activation at the plasma membrane. However, the stimulatory effects of these mutants were reduced compared with WT CLC-5. Furthermore, gene silencing experiments confirmed the functional coupling between V-ATPase and CLC-5 at the plasma membrane of isolated mouse PTs. These results reveal for the first time that the conversion of CLC-5 from a 2Cl−/H+ exchanger into a Cl− channel induces Dent’s disease in humans. In addition, defective endosomal acidification as a result of insufficient V-ATPase activation may still be important in the pathogenesis of Dent’s disease.

Strong Association of the HLA-DR/DQ Locus with Childhood Steroid-Sensitive Nephrotic Syndrome in the Japanese Population

Background Nephrotic syndrome is the most common cause of chronic glomerular disease in children. Most of these patients develop steroid-sensitive nephrotic syndrome (SSNS), but the loci conferring susceptibility to childhood SSNS are mainly unknown.Methods We conducted a genome-wide association study (GWAS) in the Japanese population; 224 patients with childhood SSNS and 419 adult healthy controls were genotyped using the Affymetrix Japonica Array in the discovery stage. Imputation for six HLA genes (HLA-A, -C, -B, -DRB1, -DQB1, and -DPB1) was conducted on the basis of Japanese-specific references. We performed genotyping for HLA-DRB1/-DQB1 using a sequence-specific oligonucleotide-probing method on a Luminex platform. Whole-genome imputation was conducted using a phased reference panel of 2049 healthy Japanese individuals. Replication was performed in an independent Japanese sample set including 216 patients and 719 healthy controls. We genotyped candidate single-nucleotide polymorphisms using the DigiTag2 assay.Results The most significant association was detected in the HLA-DR/DQ region and replicated (rs4642516 [minor allele G], combined Pallelic=7.84×10-23; odds ratio [OR], 0.33; 95% confidence interval [95% CI], 0.26 to 0.41; rs3134996 [minor allele A], combined Pallelic=1.72×10-25; OR, 0.29; 95% CI, 0.23 to 0.37). HLA-DRB1*08:02 (Pc=1.82×10-9; OR, 2.62; 95% CI, 1.94 to 3.54) and HLA-DQB1*06:04 (Pc=2.09×10-12; OR, 0.10; 95% CI, 0.05 to 0.21) were considered primary HLA alleles associated with childhood SSNS. HLA-DRB1*08:02-DQB1*03:02 (Pc=7.01×10-11; OR, 3.60; 95% CI, 2.46 to 5.29) was identified as the most significant genetic susceptibility factor.Conclusions The most significant association with childhood SSNS was detected in the HLA-DR/DQ region. Further HLA allele/haplotype analyses should enhance our understanding of molecular mechanisms underlying SSNS.