Haruhiko Hirai

An Overgrowth Disorder Associated with Excessive Production of cGMP Due to a Gain-of-Function Mutation of the Natriuretic Peptide Receptor 2 Gene

We describe a three-generation family with tall stature, scoliosis and macrodactyly of the great toes and a heterozygous p.Val883Met mutation in Npr2, the gene that encodes the CNP receptor NPR2 (natriuretic peptide receptor 2). When expressed in HEK293A cells, the mutant Npr2 cDNA generated intracellular cGMP (cyclic guanosine monophosphate) in the absence of CNP ligand. In the presence of CNP, cGMP production was greater in cells that had been transfected with the mutant Npr2 cDNA compared to wild-type cDNA. Transgenic mice in which the mutant Npr2 was expressed in chondrocytes driven by the promoter and intronic enhancer of the Col11a2 gene exhibited an enhanced production of cGMP in cartilage, leading to a similar phenotype to that observed in the patients. In addition, blood cGMP concentrations were elevated in the patients. These results indicate that p.Val883Met is a constitutive active gain-of-function mutation and elevated levels of cGMP in growth plates lead to the elongation of long bones. Our findings reveal a critical role for NPR2 in skeletal growth in both humans and mice, and may provide a potential target for prevention and treatment of diseases caused by impaired production of cGMP.

Circulating Levels of Soluble α-Klotho Are Markedly Elevated in Human Umbilical Cord Blood

CONTEXT Fetal serum levels of calcium and phosphate are higher than those in the maternal levels. Although α-Klotho is known to participate in calcium and phosphate metabolism in adults, its role in the perinatal period remains unknown. OBJECTIVE This study aimed to determine the baseline levels of soluble α-Klotho in fetuses and compare them with those in neonates, mothers, and adults to clarify whether α-Klotho is involved in the fetal-specific regulation of calcium and phosphate metabolism. DESIGN AND SETTING We conducted a cross-sectional evaluation of healthy babies (at birth and/or at 4 d after birth), their mothers, and adult volunteers at one hospital. PARTICIPANTS Twenty-one healthy mothers, their babies (23 in total, including two pairs of twins), and 25 adult volunteers participated in the study. MAIN OUTCOME MEASURES We measured the serum levels of soluble α-Klotho and fibroblast growth factor 23 (FGF23). RESULTS In cord blood, the level of α-Klotho was markedly higher (3243 ± 1899 pg/ml) than levels in neonates at d 4 (582 ± 90 pg/ml), mothers (768 ± 261 pg/ml), and adult volunteers (681 ± 140 pg/ml) (P < 0.001), whereas the fetal level of FGF23 was lower than levels in the other subjects. The levels of soluble α-Klotho were negatively correlated with those of FGF23 in cord blood. Immunohistochemistry demonstrated that α-Klotho was predominantly expressed in syncytiotrophoblasts in normal term placenta. CONCLUSION Levels of soluble α-Klotho are markedly elevated in cord blood and might be useful as a biomarker for mineral metabolism in the fetus.

Examination of megalin in renal tubular epithelium from patients with Dent disease

Dent disease is characteristic for the urinary loss of low-molecular-weight proteins and calcium, leading to renal calcification and, in some patients, chronic renal failure. This disorder is caused by loss-of-function mutations in the renal chloride channel gene, CLCN5. The animal model of this disease has demonstrated the possible role of disturbed megalin expression, which is a member of the low-density lipoprotein receptor family and is associated with renal reabsorption of a variety of proteins, in Dent disease. We examined the expression of megalin in the renal tubular epithelium of two unrelated patients with Dent disease. One patient, whose CLCN5 gene was completely deleted, showed significantly decreased staining of megalin compared with controls, while there was no change in another patient with partial deletion of the gene. These results demonstrated that mutation of CLCN5 in some patients with Dent disease may impair the expression of megalin, resulting in abnormal calcium metabolism, manifested as hypercalciuria and nephrocalcinosis.

A novel activating mutation (C129S) in the calcium-sensing receptor gene in a Japanese family with autosomal dominant hypocalcemia.

AbstractAutosomal dominant hypocalcemia can be caused by activating mutations of the calcium-sensing receptor (CaSR) gene. We experienced two patients (proband and her daughter) with hypocalcemia caused by a missense mutation of the CaSR gene. The proband, aged 25, showed hypocalcemia and hypoparathyroidism from infancy. She had been diagnosed as having idiopathic hypoparathyroidism and had been treated with calcitriol. She gave birth to a female infant at age 24 years. Her daughter was found to have hypocalcemia (Ca, 6.6 mg/dl), without seizure or tetany, when she was 7 months old. DNA analysis of their CaSR genes showed a novel heterozygous mutation at codon 129 (TGC-to-AGC) with substitution of cysteine for serine (C129S). Familial examination revealed that this mutation had occurred de-novo in the proband. Wild-type and mutant (C129S) CaSR cDNA were transfected into HEK293 cells, and intracellular calcium concentrations were measured with a fluorescent calcium indicator. HEK cells transfected with the C129S mutant CaSR gene showed a larger increase in intracellular calcium concentration in response to the change in the extracellular calcium concentration than HEK cells transfected with the wild-type receptor. We conclude that the C129S mutation in the CaSR gene observed in these patients causes autosomal dominant hypocalcemia.

Successful stenting for renal artery stenosis in a patient with Alagille syndrome.

A 12-year-old girl with Alagille syndrome manifested severe hypertension caused by renal artery stenosis in a solitary functioning kidney. Percutaneous transluminal angioplasty (PTA) and stenting was performed, but the hypertension persisted. On the next day, acute renal failure occurred with the administration of angiotensin-converting enzyme inhibitor, and migration of the stent was confirmed by angiography. Thus, a second stent was placed with success. Since then, the hypertension has been controlled with anti-hypertensive medication, and the renal function has recovered to normal range.

Interferon treatment on glomerulonephritis associated with hepatitis C virus

Abstract We report on a 10-year-old girl with glomerulonephritis associated with hepatitis C virus infection, who was treated with interferon-α. On the first renal biopsy at 8 years of age, mild mesangial hypercellularity in a segmental to semiglobal pattern was present in all glomeruli. After 6 months interferon-α therapy, proteinuria diminished completely. However, mesangial proliferation was advanced on the second biopsy at 10 years of age. We concluded that the interferon-α was effective in the treatment of proteinuria despite the lack of pathological improvement.

Long-term hospitalization during pregnancy is a risk factor for vitamin D deficiency in neonates

Abstract. In order to examine the effects of long-term hospitalization during pregnancy on vitamin D metabolism in pregnant women and neonates, we measured the serum 25-hydroxyvitamin D (25OHD) levels in pregnant women, as well as measuring 25OHD levels in cord blood and breast milk. In pregnant women hospitalized for longer than 1 month, the serum 25OHD levels were decreased at delivery compared with those in control subjects (10.9 ± 2.6 ng/l vs 19.5 ± 4.9 ng/l; P < 0.01). Although the levels of 25OHD in the cord blood were not significantly different between the long-term hospitalized and control pregnant women in this study (9.36 ± 1.7 ng/l vs 11.1 ± 3.0 ng/l), the 25OHD concentrations in the cord blood were significantly lower than the maternal levels in both groups; the ratios of the levels in cord blood to sera in the long-term hospitalized women and control subjects were 82.1% and 60.3%, respectively. Long maternal hospitalization does not always cause neonatal vitamin D deficiency, but could be one of its major risk factors. Therefore, sufficient sunlight exposure and intake of sufficient vitamin D are considered to be important to prevent vitamin D deficiency in long-term hospitalized pregrant women as well as their babies.

A Japanese Male Patient with ‘Fibular Aplasia, Tibial Campomelia and Oligodactyly’: An Additional Case Report

We report a male infant with FATCO syndrome, an acronym for fibular aplasia, tibial campomelia, and oligosyndactyly. Courtens et al. reported an infant with oligosyndactyly of the left hand, complete absence of the right fibula, bowing of the right tibia, and absence of the right fifth metatarsal and phalanges. They noted 5 patients with similar clinical features, and proposed the FATCO syndrome. Our patient had a left-sided cleft lip, cleft palate, oligosyndactyly of the right hand and bilateral feet, and bilateral anterior bowing of the limbs associated with overlying skin dimpling. Radiographs showed a short angulated tibia with left fibular aplasia and right fibular hypoplasia. We consider our case the 6th patient with FATCO syndrome, and the cleft lip and palate, not reported in the previous 5 patients, may allow us to further understand the development of the extremities and facies.

A Spectrum of Clinical Presentations in Seven Japanese Patients with Vitamin D Deficiency

Recently, the reemergence of vitamin D deficiency in developed countries has been pointed out. Vitamin D deficiency is diagnosed based on the serum 25-hydroxyvitamin D (25OHD) level. However, its normal range is still controversial, making the diagnosis of vitamin D deficiency difficult. Here, we present seven Japanese patients diagnosed with vitamin D deficiency. Three patients complained of leg bowing, and the other four of tetany. The patients with leg bowing were toddlers. Radiographic surveys demonstrated evidence of rickets. Laboratory findings showed decreased levels of serum inorganic phosphorus and increased levels of alkaline phosphatase (ALP) and intact-parathyroid hormone (iPTH). The serum levels of 25OHD were relatively low, ranging from 13 to 15.2 ng/ml. Of the patients with tetany, three were young infants. Laboratory findings showed decreased levels of serum calcium and increased levels of ALP and iPTH. The serum levels of 25OHD were markedly decreased (below 8 ng/ml). Thus, these results indicate that relatively low levels of 25OHD can cause rickets, a symptom of vitamin D deficiency, and that clinicians should therefore carefully evaluate the levels of 25OHD.

Development of hyperthyroidism in a patient with idiopathic nephrotic syndrome

Abstract We present a 13-year-old boy who developed hyperthyroidism during the clinical course of idiopathic nephrotic syndrome treated with glucocorticoid. He had a second relapse of minimal change nephrotic syndrome, and complete remission of nephrotic syndrome was achieved immediately with oral glucocorticoid. However, when the steroid dosage was reduced, signs of hyperthyroidism such as systolic hypertension and tachycardia were observed. Laboratory findings revealed thyroid-stimulating hormone (TSH) below 0.05 µU/ml, free tri-iodothyronine of 16.1 pg/ml, free thyroxine of 5.6 ng/dl, and anti-TSH receptor antibody of 90%. Thus, a diagnosis of hyperthyroidism was made and treatment with thiamazol was started. Massive proteinuria may decrease the activity of hyperthyroidism due to urinary loss of thyroid hormones. A decrease in glucocorticoid dosage may also be involved in the development of hyperthyroidism due to a reduced immunosuppressive effect.