Kenichi Satomura

The Pharmacological Characteristics of Molecular-Based Inherited Salt-Losing Tubulopathies

CONTEXT Our understanding of inherited salt-losing tubulopathies has improved with recent advances in molecular genetics. However, the terminology of Bartter syndrome and Gitelman syndrome does not always accurately reflect their pathophysiological basis or clinical presentation, and some patients are difficult to diagnose from their clinical presentations. OBJECTIVE In the present study, we conducted molecular analysis and diuretic tests for patients with inherited salt-losing tubulopathies to clarify the pharmacological characteristics of these disorders. PATIENTS We detected mutations and subsequently conducted diuretic tests using furosemide and thiazide for 16 patients with salt-losing tubulopathies (two with SLC12A1; two with KCNJ1; nine with CLCNKB; and three with SLC12A3). RESULTS Patients with SLC12A1 mutations showed no response to furosemide, whereas those with SLC12A3 mutations showed no response to thiazide. However, patients with CLCNKB mutations showed no response to thiazide and a normal response to furosemide, and those with KCNJ1 mutations showed a good response to both diuretics. This study revealed the following characteristics of these disorders: 1) subjects with CLCNKB mutations showed one or more biochemical features of Gitelman syndrome (including hypomagnesemia, hypocalciuria, and fractional chloride excretion insensitivity to thiazide administration); and 2) subjects with KCNJ1 mutations appeared to show normal fractional chloride excretion sensitivity to furosemide and thiazide administration. CONCLUSIONS These results indicate that these disorders are difficult to distinguish in some patients, even when using diuretic challenge. This clinical report provides important findings that can improve our understanding of inherited salt-losing tubulopathies and renal tubular physiology.

Molecular analysis of patients with type III bartter syndrome : Picking up large heterozygous deletions with semiquantitative PCR

Type III Bartter syndrome (BS) (OMIM607364) is caused by mutations in the basolateral chloride channel ClC-Kb gene (CLCNKB). The CLCNKB gene is sometimes reported as having a large deletion mutation, but all cases reported previously were large homozygous deletions and a large heterozygous deletion is impossible to detect by direct sequencing. This report concerns a genetic analysis of five Japanese patients with type III BS. To identify the mutations, we used polymerase chain reaction (PCR) and direct sequencing. To detect large heterozygous deletion mutations of the CLCNKB gene, we conducted semiquantitative PCR amplification using capillary electrophoresis. The result was that four mutations were identified, comprising one novel 2-bp deletion mutation, an entire heterozygous deletion, and a heterozygous deletion mutation of exons 1 and 2. The nonsense mutation W610X was detected in all patients, and this mutation is likely to constitute a founder effect in Japan. Capillary electrophoresis is a new method and extremely useful for detecting large heterozygous deletions, and should be used to examine type III BS cases in whom only a heterozygous mutation has been detected by direct sequencing. This is the first report to identify large heterozygous deletion mutations in the CLCNKB gene in patients with type III BS.

Risk factors for developing severe clinical course in HUS patients: a national survey in Japan

Background: Hemolytic uremic syndrome (HUS) is characterized by acute renal failure, thrombocytopenia and hemolytic anemia. Cases accompanied by prodromal gastrointestinal tract symptoms are referred to as typical HUS. Some severe HUS patients require dialysis or develop central nervous system (CNS) disorders after the onset of HUS.

EYA1 and SIX1 gene mutations in Japanese patients with branchio-oto-renal (BOR) syndrome and related conditions

We isolated genomic DNA from 15 patients with branchio-oto-renal (BOR) syndrome or BOR-related conditions. Seven patients had BOR syndrome (two familial and five sporadic), and eight had deafness and renal malformations without branchial fistula (BOR-related conditions). We analyzed all exons and exon–intron boundaries of EYA1 and SIX1 using the polymerase chain reaction (PCR) direct sequencing, and characterized their mutations. In some patients, analysis of mRNA by reverse transcription (RT)-PCR was performed to examine whether the mutation affects the mRNA splicing. We identified five novel disease-causing heterozygous EYA1 mutations in five patients with BOR syndrome (two familial and three sporadic, 5/7=71%), but EYA1 and SIX1 mutations were not detected in the other two patients with BOR syndrome or any of the patients with BOR-related conditions. The detected EYA1 mutations were two nonsense mutations, two splicing acceptor-site mutations, and a point mutation (G>T) of the first base of exon 10. Analysis of mRNA by RT-PCR direct sequencing revealed that the latter point mutation led to the skipping of exon 10. In conclusion, (1) EYA1 mutations are a major cause of BOR syndrome in Japanese, (2) EYA1 and SIX1 mutations were not a major cause of BOR-related conditions, (3) we demonstrated for the first time that the point mutation (G>T) of the first base of the exon in EYA1 gene induced exon skipping.

Proteinuria and glomerular hypertrophy in extremely low-birthweight children

Of late, there is an increased awareness of the frequent occurrence of hypertension or proteinuria in adults born at low birthweight.

Risk factors associated with a decreased estimated glomerular filtration rate based on cystatin C levels in school-age children with extremely low birth weight.

A single centre retrospective cohort study was designed to investigate the estimated glomerular filtration rate (eGFR) in school‐age children born with extremely low birthweight (ELBW) and to determine risk factors predictive of decreased eGFR.