Kandai Nozu

Differential diagnosis of Bartter syndrome, Gitelman syndrome, and pseudo–Bartter/Gitelman syndrome based on clinical characteristics

Purpose:Phenotypic overlap exists among type III Bartter syndrome (BS), Gitelman syndrome (GS), and pseudo-BS/GS (p-BS/GS), which are clinically difficult to distinguish. We aimed to clarify the differences between these diseases, allowing accurate diagnosis based on their clinical features.Methods:A total of 163 patients with genetically defined type III BS (n = 30), GS (n = 90), and p-BS/GS (n = 43) were included. Age at diagnosis, sex, body mass index, estimated glomerular filtration rate, and serum and urine electrolyte concentrations were determined.Results:Patients with p-BS/GS were significantly older at diagnosis than those with type III BS and GS. Patients with p-BS/GS included a significantly higher percentage of women and had a lower body mass index and estimated glomerular filtration rate than did patients with GS. Although hypomagnesemia and hypocalciuria were predominant biochemical findings in patients with GS, 17 and 23% of patients with type III BS and p-BS/GS, respectively, also showed these abnormalities. Of patients with type III BS, GS, and p-BS/GS, 40, 12, and 63%, respectively, presented with chronic kidney disease.Conclusions:This study clarified the clinical differences between BS, GS, and p-BS/GS for the first time, which will help clinicians establish differential diagnoses for these three conditions.Genet Med 18 2, 180–188.

Genetic, Clinical, and Pathologic Backgrounds of Patients with Autosomal Dominant Alport Syndrome

BACKGROUND AND OBJECTIVESnAlport syndrome comprises a group of inherited heterogeneous disorders involving CKD, hearing loss, and ocular abnormalities. Autosomal dominant Alport syndrome caused by heterozygous mutations in collagen 4A3 and/or collagen 4A4 accounts for <5% of patients. However, the clinical, genetic, and pathologic backgrounds of patients with autosomal dominant Alport syndrome remain unclear.nnnDESIGN, SETTING, PARTICIPANTS, & MEASUREMENTSnWe conducted a retrospective analysis of 25 patients with genetically proven autosomal dominant Alport syndrome and their family members (a total of 72 patients) from 16 unrelated families. Patients with suspected Alport syndrome after pathologic examination who were referred from anywhere in Japan for genetic analysis from 2006 to 2015 were included in this study. Clinical, laboratory, and pathologic data were collected from medical records at the point of registration for genetic diagnosis. Genetic analysis was performed by targeted resequencing of 27 podocyte-related genes, including Alport-related collagen genes, to make a diagnosis of autosomal dominant Alport syndrome and identify modifier genes or double mutations. Clinical data were obtained from medical records.nnnRESULTSnThe median renal survival time was 70 years, and the median age at first detection of proteinuria was 17 years old. There was one patient with hearing loss and one patient with ocular lesion. Among 16 patients who underwent kidney biopsy, three showed FSGS, and seven showed thinning without lamellation of the glomerular basement membrane. Five of 13 detected mutations were reported to be causative mutations for autosomal recessive Alport syndrome in previous studies. Two families possessed double mutations in both collagen 4A3 and collagen 4A4, but no modifier genes were detected among the other podocyte-related genes.nnnCONCLUSIONSnThe renal phenotype of autosomal dominant Alport syndrome was much milder than that of autosomal recessive Alport syndrome or X-linked Alport syndrome in men. It may, thus, be difficult to make an accurate diagnosis of autosomal dominant Alport syndrome on the basis of clinical or pathologic findings. No modifier genes were identified among the known podocyte-related genes.

Long-term outcome of childhood-onset complicated nephrotic syndrome after a multicenter, double-blind, randomized, placebo-controlled trial of rituximab

BackgroundAlthough rituximab effectively prevents relapses of complicated frequently relapsing nephrotic syndrome (FRNS) and steroid-dependent nephrotic syndrome (SDNS), data of long-term outcomes and safety are limited.MethodsFifty-one patients (age, 3–38xa0years) with childhood-onset complicated FRNS or SDNS, who received rituximab in investigator-initiated multicenter prospective trials were enrolled. Rituximab was administered at 375xa0mg/m2 once weekly for 4xa0weeks, and immunosuppressive agents were discontinued according to the study protocol. We investigated relapses, re-administration of immunosuppressive agents, additional rituximab treatment, body height, renal function, and late adverse events during the observation period.ResultsForty-eight patients (94%) developed relapses during the observation period (median, 59xa0months) and the 50% relapse-free survival was 261xa0days. Thirty patients (59%) developed SDNS, 44 (86%) required re-administration of immunosuppressive agents, and 22 (43%) received additional rituximab treatment. All patients who were receiving immunosuppressive agents at rituximab treatment required either immunosuppressive agents or additional rituximab treatment. On the contrary, 5 of the 13 patients without immunosuppressive agents at rituximab treatment required neither immunosuppressive agents nor additional rituximab treatment and 3 of them did not develop relapse during observation period. Growth failure due to steroid toxicity did not progress and none of the patients developed chronic renal insufficiency. None of the patients suffered from rituximab-related late adverse events.ConclusionsAs most patients suffer from relapses after B-cell recovery, long-term immunosuppressive agents or additional rituximab treatment is necessary. However, some patients who can discontinue immunosuppressive agents before rituximab treatment may achieve long-term remission after rituximab treatment without immunosuppressive agents.

Natural History and Genotype-Phenotype Correlation in Female X-Linked Alport Syndrome

Introduction X-linked Alport syndrome (XLAS) is a hereditary disease characterized by progressive nephritis, hearing loss, and ocular abnormalities. Affected male patients usually progress to end-stage renal disease in early or middle adulthood, and disease severity is strongly correlated with genotype. However, the clinical course in female patients has rarely been reported. Methods We conducted a retrospective analysis of females with genetically proven XLAS (n = 275) and their affected female family members (n = 61) from 179 Japanese families. Patients suspected to have Alport syndrome from pathologic findings or a family history who were referred from anywhere in Japan for genetic diagnosis between 2006–2015 were included in this study. Clinical and laboratory data were collected from medical records at the time of registration for genetic analysis. Results Proteinuria was detected in 175 genetically proven patients (72.6%), and the median age for developing proteinuria was 7.0 years. Fifty-two of 336 patients developed end-stage renal disease with a median renal survival age of 65.0 years. No obvious genotype–phenotype correlation was observed. Additionally, targeted sequencing for podocyte-related genes in patients with severe phenotypes revealed no obvious variants considered to be modifier genes except for 1 patient with a COL4A3 gene variant. Discussion This study revealed that phenotypes in female XLAS patients may be severe, but genotype does not help to predict the disease severity. Clinicians must therefore pay careful attention to the clinical course and appropriate treatment in females with XLAS.

Cryptic exon activation in SLC12A3 in Gitelman syndrome

Gitelman syndrome (GS) is an autosomal recessive renal tubulopathy characterized by hypokalemic metabolic alkalosis with hypocalciuria and hypomagnesemia. GS clinical symptoms range from mild weakness to muscular cramps, paralysis or even sudden death as a result of cardiac arrhythmia. GS is caused by loss-of-function mutations in the solute carrier family 12 member 3 (SLC12A3) gene, but molecular mechanisms underlying such a wide range of symptoms are poorly understood. Here we report cryptic exon activation in SLC12A3 intron 12 in a clinically asymptomatic GS, resulting from an intronic mutation c.1669+297u2009T>G that created a new acceptor splice site. The cryptic exon was sandwiched between the L3 transposon upstream and a mammalian interspersed repeat downstream, possibly contributing to inclusion of the cryptic exon in mature transcripts. The mutation was identified by targeted next-generation sequencing of candidate genes in GS patients with missing pathogenic SLC12A3 alleles. Taken together, this work illustrates the power of next-generation sequencing to identify causal mutations in intronic regions in asymptomatic individuals at risk of developing potentially fatal disease complications, improving clinical management of these cases.

A comparison of splicing assays to detect an intronic variant of the OCRL gene in Lowe syndrome

Lowe syndrome is an X-linked inherited disorder diagnosed by congenital cataracts, intellectual impairment, and renal tubular dysfunction. It is caused by pathogenic variants of the oculocerebrorenal syndrome of Lowe gene (OCRL), of which more than 250 have been reported so far. Around 30 of these variants are intronic nucleotide changes; however, to show the pathogenicity of these variants is usually laborious. In this report, we conducted genetic testing of a patient clinically diagnosed with Lowe syndrome to detect the presence of OCRL variants. We analyzed variant transcript expression in peripheral blood leukocytes and using a minigene construct in addition to in silico analysis. We detected a 9 base pair intronic insertion between OCRL exon 10 and exon 11 derived from the alteration of the splicing acceptor site in intron 10 caused by the intronic splicing variant NM_000276.3: c.940-11G>A (p.Lys313_Val314insAsnSer*). The findings obtained from transcript analysis of peripheral blood leukocytes and the minigene construct assay were identical to those of in silico analysis. All assays detected the same transcript abnormality and were reliable in revealing the pathogenicity of the intronic variant. The inxa0vitro assay can also be used to clarify the complicated splicing mechanisms in inherited kidney diseases.

Clinical characteristics and long-term outcome of diarrhea-associated hemolytic uremic syndrome: a single center experience

ObjectivesTo clarify the clinical characteristics and long-term outcomes of patients with diarrhea-associated hemolytic uremic syndrome (Du2009+u2009HUS) with a particular focus on time course.MethodsWe retrospectively analyzed the medical records of 61 patients with Du2009+u2009HUS who were admitted to Kobe University Hospital between 1995 and 2015. The onset of Du2009+u2009HUS was defined as day 1 of diarrhea.ResultsThe age of onset was 4.1 (1.5–13.4) years, and the period between onset and diagnosis of Du2009+u2009HUS was 5 (3–18) days. The platelet count was lowest on day 7 (4–24), and the lactase dehydrogenase level was maximal on day 8 (4–25). Twenty-three patients required dialysis for 13 (2–37) days, starting at day 5–9. Seventeen patients showed central nervous system (CNS) symptoms at day 4–18. They were followed up for 3.7 (0–18.4) years. At the final follow-up, estimated glomerular filtration rate was 113.7 (57.9–159.9) ml/min/1.73xa0m2 with five patients having chronic kidney disease. Three patients developed CNS sequelae. The time to diagnosis was significantly shorter in the group of patients receiving dialysis than without dialysis (pu2009=u20090.018) and in the group with CNS complications than without (pu2009=u20090.013).ConclusionCNS complications were often apparent after blood examination results improved. Moreover, a shorter period between the onset of diarrhea and a diagnosis of Du2009+u2009HUS indicated a more severe clinical course or long-term sequelae, and it should be considered as a risk factor for poor prognosis.

Pathogenesis of hypokalemia in autosomal dominant hypocalcemia type 1

BackgroundAutosomal dominant hypocalcemia type 1 (ADH1) is a relatively rare endocrine disorder characterized by hypocalcemia and inadequate parathyroid hormone secretion. ADH is caused by activating mutations in the calcium-sensing receptor (CaSR) gene, CASR. CaSR plays a crucial role in calcium and magnesium homeostasis in the kidney. ADH may be accompanied by hypokalemia and metabolic alkalosis when it is classified as type V Bartter syndrome. However, the mechanism underlying hypokalemia in this disease is unclear.MethodsWe investigated a 33-year-old woman with hypocalcemia and hypoparathyroidism since childhood, whose mother also had hypocalcemia and hypoparathyroidism, but with no clinical symptoms. Blood examinations showed hypokalemia and metabolic alkalosis in the patient, but not her mother. We conducted mutation analysis and diuretic tests to clarify the patient’s and her mother’s diagnosis and to investigate the onset mechanism of hypokalemia in ADH1. We also determined the localization of CaSR in the kidney by immunohistochemistry.ResultsWe detected a known gain-of-function mutation in CASR in both the patient and her mother. Diuretic tests revealed a response to furosemide and no reaction to thiazide in the patient, although the mother responded well to both diuretics. CaSR co-localized with the Na+–Cl− cotransporter (NCCT) on distal tubular epithelial cells.ConclusionsThese results indicate that the NCCT in the distal convoluted tubule was secondarily affected in this patient. We conclude that the main pathogenesis of secondary hypokalemia in ADH1 in this patient was secondary NCCT dysfunction.

IgA nephropathy with presentation of nephrotic syndrome at onset in children

BackgroundDespite a low incidence, nephrotic syndrome (NS) can present with IgA nephropathy (IgAN). The clinical characteristics and long-term outcomes of pediatric patients with IgAN presenting with NS (NS-IgAN) at onset have not been fully elucidated.MethodsWe retrospectively analyzed 426 patients, and compared clinical and pathological (Oxford) findings between those with NS-IgAN and those with non-NS-IgAN.ResultsAmong 426 patients, 30 (7.0xa0%) had NS-IgAN. Logistic analyses showed that male sex (OR: 7.6, pu2009=u20090.0002), M1 (OR: 10.3, pu2009=u20090.002), and E1 (OR: 15.2, pu2009=u20090.0001) were significantly related to NS. The mean observation period was 6.2u2009±u20093.2xa0years. Although NS-IgAN was associated with significantly lower renal survival than non-NS-IgAN according to Kaplan–Meier analysis (pu2009=u20090.02), renal survival of NS-IgAN was good (92.4xa0% at 10xa0years). The most significant prognostic factor for renal survival was remission of proteinuria after treatment, and NS at onset is also a significant prognostic factor for renal survival after adjusting for remission of proteinuria. Twenty children with NS-IgAN were treated with prednisolone alone, or prednisolone and immunosuppressant. Remission of proteinuria occurred in 21 patients. Three cases of NS-IgAN progressed to stage III–V chronic kidney disease at the most recent observation. They all demonstrated heavy proteinuria after the 2-year initial treatment. The significant factor for persistent proteinuria at 5xa0years was S1 in NS-IgAN.ConclusionsThe most significant factor for renal survival was responsiveness to treatment, not NS itself. As modifiable acute lesions are the dominant pathological findings in NS-IgAN, histological improvements achieved by appropriate treatments can result in a favorable prognosis.

A birth of bipartite exon by intragenic deletion

Disease‐causing mutations that activate transposon‐derived exons without creating a new splice‐site consensus have been reported rarely, but they provided unique insights into our understanding of structural motifs required for inclusion of intronic sequences in mature transcripts.