Yasufumi Ohtsuka

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.

A novel de novo point mutation of the OCT-binding site in the IGF2/H19-imprinting control region in a Beckwith–Wiedemann syndrome patient

The IGF2/H19‐imprinting control region (ICR1) functions as an insulator to methylation‐sensitive binding of CTCF protein, and regulates imprinted expression of IGF2 and H19 in a parental origin‐specific manner. ICR1 methylation defects cause abnormal expression of imprinted genes, leading to Beckwith–Wiedemann syndrome (BWS) or Silver–Russell syndrome (SRS). Not only ICR1 microdeletions involving the CTCF‐binding site, but also point mutations and a small deletion of the OCT‐binding site have been shown to trigger methylation defects in BWS. Here, mutational analysis of ICR1 in 11 BWS and 12 SRS patients with ICR1 methylation defects revealed a novel de novo point mutation of the OCT‐binding site on the maternal allele in one BWS patient. In BWS, all reported mutations and the small deletion of the OCT‐binding site, including our case, have occurred within repeat A2. These findings indicate that the OCT‐binding site is important for maintaining an unmethylated status of maternal ICR1 in early embryogenesis.

Homozygous deletion of DIS3L2 exon 9 due to non-allelic homologous recombination between LINE-1s in a Japanese patient with Perlman syndrome

Perlman syndrome is a rare, autosomal recessive overgrowth disorder. Recently, the deletion of exon 9 and other mutations of the DIS3L2 gene have been reported in patients; however, the mechanism behind this deletion is still unknown. We report the homozygous deletion of exon 9 of DIS3L2 in a Japanese patient with Perlman syndrome. We identified the deletion junction, and implicate a non-allelic homologous recombination (NAHR) between two LINE-1 (L1) elements as the causative mechanism. Furthermore, the deletion junctions were different between the paternal and maternal mutant alleles, suggesting the occurrence of two independent NAHR events in the ancestors of each parent. The data suggest that the region around exon 9 might be a hot spot of L1-mediated NAHR.

Alport syndrome caused by a COL4A5 deletion and exonization of an adjacent AluY.

Mutation‐induced activation of splice sites in intronic repetitive sequences has contributed significantly to the evolution of exon–intron structure and genetic disease. Such events have been associated with mutations within transposable elements, most frequently in mutation hot‐spots of Alus. Here, we report a case of Alu exonization resulting from a 367‐nt genomic COL4A5 deletion that did not encompass any recognizable transposed element, leading to the Alport syndrome. The deletion brought to proximity the 5′ splice site of COL4A5 exon 33 and a cryptic 3′ splice site in an antisense AluY copy in intron 32. The fusion exon was depleted of purines and purine‐rich splicing enhancers, but had low levels of intramolecular secondary structure, was flanked by short introns and had strong 5′ and Alu‐derived 3′ splice sites, apparently compensating poor composition and context of the new exon. This case demonstrates that Alu splice sites can be activated by outlying deletions, highlighting Alu versatility in shaping the exon–intron organization and expanding the spectrum of mutational mechanisms that introduce repetitive sequences in mRNAs.

Identification of consensus motifs associated with mitotic recombination and clinical characteristics in patients with paternal uniparental isodisomy of chromosome 11

Uniparental disomy (UPD) is defined as the inheritance of both homologs of a given genomic region from only one parent. The majority of UPD includes an entire chromosome. However, the extent of UPD is sometimes limited to a subchromosomal region (segmental UPD). Mosaic paternal UPD (pUPD) of chromosome 11 is found in approximately 20% of patients with Beckwith-Wiedemann syndrome (BWS) and almost all pUPDs are segmental isodisomic pUPDs resulting from mitotic recombination at an early embryonic stage. A mechanism initiating a DNA double strand break (DSB) within 11p has been predicted to lead to segmental pUPD. However, no consensus motif has yet been found. Here, we analyzed 32 BWS patients with pUPD by SNP array and searched for consensus motifs. We identified four consensus motifs frequently appearing within breakpoint regions of segmental pUPD. These motifs were found in another nine BWS patients with pUPD. In addition, the seven motifs found in meiotic recombination hot spots could not be found within pUPD breakpoint regions. Histone H3 lysine 4 trimethylation, a marker of DSB initiation, could not be found either. These findings suggest that the mechanism(s) of mitotic recombination leading to segmental pUPD are different from that of meiotic recombination. Furthermore, we found seven patients with paternal uniparental diploidy (PUD) mosaicism. Comparison of clinical features between segmental pUPDs and PUDs showed that developmental disability and cardiac abnormalities were additional characteristic features of PUD mosaicism, along with high risk of tumor development. We also found that macroglossia was characteristic of segmental pUPD mosaicism.

Autosomal recessive cystinuria caused by genome-wide paternal uniparental isodisomy in a patient with Beckwith-Wiedemann syndrome.

Approximately 20% of Beckwith–Wiedemann syndrome (BWS) cases are caused by mosaic paternal uniparental disomy of chromosome 11 (pUPD11). Although pUPD11 is usually limited to the short arm of chromosome 11, a small minority of BWS cases show genome‐wide mosaic pUPD (GWpUPD). These patients show variable clinical features depending on mosaic ratio, imprinting status of other chromosomes, and paternally inherited recessive mutations. To date, there have been no reports of a mosaic GWpUPD patient with an autosomal recessive disease caused by a paternally inherited recessive mutation. Here, we describe a patient concurrently showing the clinical features of BWS and autosomal recessive cystinuria. Genetic analyses revealed that the patient has mosaic GWpUPD and an inherited paternal homozygous mutation in SLC7A9. This is the first report indicating that a paternally inherited recessive mutation can cause an autosomal recessive disease in cases of GWpUPD mosaicism. Investigation into recessive mutations and the dysregulation of imprinting domains is critical in understanding precise clinical conditions of patients with mosaic GWpUPD.

Postoperative Atypical Hemolytic Uremic Syndrome Treated Successfully with Eculizumab

Atypical hemolytic uremic syndrome (aHUS) is a rare type of HUS associated with dysregulation of the alternative complement pathway. We herein report the findings of a 43-year-old woman who developed aHUS two days after myomectomy. The serum C3 level was low and the sheep erythrocyte hemolytic assay showed a moderate hemolysis. The renal insufficiency progressed despite performing plasma exchange therapy, although a partial hematological response was observed. Thus, the patient was subsequently treated with the anti-C5 antibody eculizumab, which promptly improved and normalized the renal function. Although aHUS after surgery has rarely been reported, it needs to be promptly recognized and treated with eculizumab to prevent irreversible renal damage.

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.

Clinically diverse phenotypes and genotypes of patients with branchio-oto-renal syndrome

Branchio-oto-renal (BOR) syndrome is a rare autosomal dominant disorder characterized by branchiogenic anomalies, hearing loss, and renal anomalies. The aim of this study was to reveal the clinical phenotypes and their causative genes in Japanese BOR patients. Patients clinically diagnosed with BOR syndrome were analyzed by direct sequencing, multiplex ligation-dependent probe amplification (MLPA), array-based comparative genomic hybridization (aCGH), and next-generation sequencing (NGS). We identified the causative genes in 38/51 patients from 26/36 families; EYA1 aberrations were identified in 22 families, SALL1 mutations were identified in two families, and SIX1 mutations and a 22q partial tetrasomy were identified in one family each. All patients identified with causative genes suffered from hearing loss. Second branchial arch anomalies, including a cervical fistula or cyst, preauricular pits, and renal anomalies, were frequently identified (>60%) in patients with EYA1 aberrations. Renal hypodysplasia or unknown-cause renal insufficiency was identified in more than half of patients with EYA1 aberrations. Even within the same family, renal phenotypes often varied substantially. In addition to direct sequencing, MLPA and NGS were useful for the genetic analysis of BOR patients.