Yuka Kinoshita

Impaired glucose metabolism in Japanese patients with acromegaly is restored after successful pituitary surgery if pancreatic β-cell function is preserved

OBJECTIVE Impaired glucose metabolism is common in acromegaly, but it is not clear how glucose metabolism is impaired or what predicts its restoration after cure of the disease. To identify factors involved in the impairment of glucose metabolism in acromegaly, we evaluated clinical parameters before and immediately after surgical cure of the disease. DESIGN AND METHODS We retrospectively analyzed clinical data of 92 consecutive Japanese patients with acromegaly who underwent successful pituitary surgery. Patients who had received medical therapy for acromegaly or insulin treatment for diabetes were excluded. We evaluated insulin resistance (IR) and pancreatic β-cell function in addition to GH and IGF1 levels before and after surgery. Results In this study of Japanese patients with acromegaly, average body mass index (BMI) was 23.4, and no patient had a BMI>30. IR was involved in the impairment of glucose metabolism, which was restored upon surgical cure of acromegaly if β-cell function was preserved. Insufficient β-cell function did not improve after normalization of GH/IGF1 and was associated with impaired glucose metabolism before and after surgery. RESULTS of receiver operating characteristic analysis of preoperative clinical parameters suggest that insulinogenic index (IGI) >0.50 best predicts restoration of normal glucose metabolism upon cure of acromegaly in Japanese patients. CONCLUSIONS IR impairs glucose metabolism in acromegaly. Once β-cell function is impaired, abnormal glucose metabolism persists even after cure of acromegaly. IGI>0.50 indicates that β-cell function is preserved in non-obese Japanese patients with acromegaly.

Hypophosphatemic osteomalacia and bone sclerosis caused by a novel homozygous mutation of the FAM20C gene in an elderly man with a mild variant of Raine syndrome

BACKGROUND Hypophosphatemia and increased serum fibroblast growth factor 23 (FGF23) levels have been reported in young brothers with compound heterozygous mutations for the FAM20C gene; however, rickets was not observed in these cases. We report an adult case of Raine syndrome accompanying hypophosphatemic osteomalacia with a homozygous FAM20C mutation (R408W) associated with increased periosteal bone formation in the long bones and an increase in bone mineral density in the femoral neck. CASE The patient, a 61-year-old man, was born from a cousin-to-cousin marriage. A short stature and severe dental demineralization were reported at an elementary school age. Hypophosphatemia was noted inadvertently at 27years old, at which time he started to take an active vitamin D metabolite (alphacalcidol) and phosphate. He also manifested ossification of the posterior longitudinal ligament. On bone biopsy performed at the age of 41years, we found severe osteomalacia surrounding osteocytes, which appeared to be an advanced form of periosteocytic hypomineralized lesions compared to those reported in patients with X-linked hypophosphatemic rickets. Laboratory data at 61years of age revealed markedly increased serum intact-FGF23 levels, which were likely to be the cause of hypophosphatemia and the decreased level of 1,25(OH)2D. We recently identified a homozygous FAM20C mutation, which was R408W, in this patient. When expressed in HEK293 cells, the R408W mutant protein exhibited impaired kinase activity and secretion. DISCUSSION Our findings suggest that certain homozygous FAM20C mutations can cause FGF23-related hypophosphatemic osteomalacia and indicate the multiple roles of FAM20C in bone.

Functional Activities of Mutant Calcium-Sensing Receptors Determine Clinical Presentations in Patients With Autosomal Dominant Hypocalcemia

OBJECTIVE Autosomal dominant hypocalcemia (ADH) is a congenital isolated hypoparathyroidism caused by activating mutations in the calcium-sensing receptor (CASR) gene. The clinical features of ADH are heterogeneous; some patients are asymptomatic, and others show severe hypocalcemia with Bartters syndrome. We therefore recruited 12 patients with ADH to clarify the determinants of their clinical presentation. DESIGN AND METHODS We studied two sporadic and 10 familial cases of ADH. Serum concentrations of calcium, intact PTH, and magnesium (Mg(2+)) were measured in each patient. Fractional excretion of Mg (FE(Mg)) was calculated in spot urine samples. A nuclear factor of activated T cells luciferase assay was used to analyze the responsiveness of each mutant CaSR to extracellular Ca(2+). RESULTS Genomic analysis revealed five known activating mutations and a novel mutation, E481K, in the CASR. Patients with the A843E, C131W, or F788C mutation showed hypomagnesemia with elevated FE(Mg). Intact PTH in these patients was consistently near the detection limit. In contrast, patients with the P221L, K47N, or E481K mutation exhibited normal Mg(2+) levels. In these patients, intact PTH increased in response to low calcium, and their maximum intact PTH exceeded the lower limit of the reference range. Functional analysis showed an association between the disease severity and the in vitro activity of the mutant CaSR. CONCLUSIONS The functional activity of mutant CaSR determines the serum Mg(2+) level, renal Mg(2+) handling, and intact PTH in patients with ADH. The presence of hypomagnesemia with elevated FE(Mg) may indicate the diagnosis of ADH among patients with PTH-deficient hypoparathyroidism.

Phosphate enhances Fgf23 expression through reactive oxygen species in UMR-106 cells.

Fibroblast growth factor 23 (FGF23) has been shown to work as a phosphotropic hormone. Although FGF23 reduces the serum phosphate level, it has not been established that phosphate directly regulates FGF23 production. In this study, we investigated whether phosphate can enhance Fgf23 expression using the rat osteoblastic cell line UMR-106, which has been shown to express Fgf23 in response to 1,25-dihydroxyvitamin D [1,25(OH)2D]. Phosphate increased Fgf23 expression in a dose- and time-dependent manner in the presence of 1,25(OH)2D. Phosphate also increased Fgf23 promoter activity, but showed no effect on the half-life of Fgf23 messenger RNA. Phosphonoformic acid and PD98059, an inhibitor of MEK, inhibited the effects of phosphate on Fgf23 expression and promoter activity. In addition, phosphate enhanced production of reactive oxygen species (ROS) in UMR-106 cells, and hydrogen peroxide enhanced FGF23 production in a dose- and time-dependent manner. Hydrogen peroxide also enhanced Elk1 reporter activity, a target of the MEK–extracellular-signal-regulated kinase (ERK) pathway. Furthermore, the effect of phosphate on ROS production and Fgf23 expression was inhibited by apocynin, an inhibitor of NADPH oxidase. These results indicate that phosphate directly enhances Fgf23 transcription without affecting the stability of Fgf23 messenger RNA by stimulating NADPH-induced ROS production and the MEK–ERK pathway in UMR-106 cells.

Functional analysis of mutant FAM20C in Raine syndrome with FGF23-related hypophosphatemia

Raine syndrome is an autosomal recessive disorder characterized by generalized osteosclerosis with periosteal bone formation and a distinctive facial phenotype. Either homozygous or compound heterozygous mutations in family with sequence similarity 20, member C (FAM20C) have been reported to cause this syndrome. Recently, it was reported that fibroblast growth factor 23 (FGF23)-related hypophosphatemia was found in patients with non-lethal Raine syndrome, and Fam20c conditional knockout mice presented Fgf23-related hypophosphatemic rickets. To clarify the mechanism of how FAM20C regulates FGF23, we performed functional analysis of mutant FAM20C proteins reported in Raine syndrome. We analyzed 6 mutant FAM20C proteins (T268M, P328S, R408W, D451N, D478A, and R549W) for their distributions, kinase activities, and effects on dentin matrix protein (DMP1) promoter activity. We also analyzed the effect of Fam20c knockdown on Dmp1 and Fgf23 mRNA levels in UMR-106 cells. As a result, all the mutant FAM20C proteins showed decreased kinase activities compared to wild-type (WT) FAM20C, and most of them also showed impaired secretion. Overexpression of WT FAM20C increased DMP1 promoter activity in Saos-2 cells while mutant FAM20C did not. Fam20c knockdown decreased Dmp1 mRNA and increased Fgf23 mRNA in UMR-106 cells. In conclusion, our results suggest that FAM20C suppresses FGF23 production by enhancing DMP1 expression, and inactivating mutations in FAM20C cause FGF23-related hypophosphatemia by decreasing transcription of DMP1.

Patients with FGF23-related hypophosphatemic rickets/osteomalacia do not present with left ventricular hypertrophy

ABSTRACT Purpose: Fibroblast growth factor 23 (FGF23) is a hormone regulating phosphate metabolism. Excessive actions of FGF23 cause several types of FGF23-related hypophosphatemic rickets/osteomalacia. Recently, it was reported that FGF23 levels were independently correlated with left ventricular hypertrophy (LVH) in patients with chronic kidney disease (CKD). In addition, FGF23 was also shown to cause cardiac hypertrophy directly acting on cardiomyocytes. However, there is no study indicating the correlation between FGF23 and LVH in adult patients with FGF23-related hypophosphatemic rickets/osteomalacia. Therefore, we examined the existence of LVH in these patients. Materials and methods: We recruited consecutive 24 patients with FGF23-related hypophosphatemic diseases. Their serum intact FGF23 levels and the parameters associated with LVH, including left ventricular mass index (LVMI), relative wall thickness (RWT), Sokolow-Lyon voltage, and Cornell product, were measured. The correlations between FGF23 and these parameters were examined. Results: The participants did not show LVH on the whole. In addition, no significant correlation was observed by these examinations. Conclusion: It seems unlikely that FGF23 levels are the apparent determinant of the cardiac mass in patients with FGF23-related hypophosphatemic rickets/osteomalacia.

Mutational analysis of patients with FGF23-related hypophosphatemic rickets

OBJECTIVE X-linked hypophosphatemic rickets (XLHR) caused by mutations in the PHEX gene is considered to be the most frequent cause of fibroblast growth factor 23 (FGF23)-related congenital hypophosphatemic rickets. In previous studies, mutations in the PHEX gene were detected in 60-70% of patients with clinical diagnoses of XLHR. This leads to the question whether current screening methods for mutations in the PHEX gene are inadequate or whether there is a substantial number of patients with other genetic causes of hypophosphatemic rickets. We conducted a genetic analysis of patients with FGF23-related hypophosphatemic rickets to clarify their etiology and evaluate the prevalence of XLHR among this group. DESIGN AND METHODS We studied 27 patients with familial and sporadic congenital hypophosphatemic rickets in whom serum FGF23 was above 30 pg/ml using an assay for the full-length protein. Exons and exon-intron junctions of genomic DNA of causative genes for FGF23-related hypophosphatemic rickets were sequenced. PHEX mRNA from peripheral blood was analyzed in some patients. RESULTS Direct sequencing of genomic DNA identified 11 novel and four known mutations in the PHEX gene. Additionally, there was a large PHEX gene deletion in one case and abnormal PHEX mRNA splicing in another. In summary, 26 patients (96%) had XLHR and one patient had autosomal recessive hypophosphatemic rickets 2. CONCLUSIONS XLHR is by far the most prevalent cause of FGF23-related hypophosphatemic rickets. We propose that analysis of PHEX mRNA from peripheral blood would be appropriate for the first screening step in determining the etiology of FGF23-related hypophosphatemic rickets.

High serum ALP level is associated with increased risk of denosumab-related hypocalcemia in patients with bone metastases from solid tumors

Metastatic bone disease is one of the most common complications of advanced cancers. Pathological fractures, spinal cord compression, and radiotherapy or surgery to the bone are collectively called skeletal-related events (SREs), which cause severe pain, increase hospitalization rates, and impair the quality of life (QOL) of patients with bone metastases. The receptor activator of nuclear factor-kB ligand (RANKL)/RANK pathway is critical in the progression of bone metastases. Previous studies have demonstrated that an anti-RANKL antibody (denosumab) was superior to zoledronic acid in prolonging time to first SRE in patients with bone metastases from prostate and breast cancers. However, severe hypocalcemic events occur more frequently after treatment with denosumab compared with zoledronic acid. In this study, 368 administrations of denosumab in 219 patients with metastatic bone disease from solid tumors were analyzed to clarify the risk factors for developing hypocalcemia. The results showed that grade 2/3 hypocalcemia was observed in 10.4% of the total number of denosumab administrations. Patients with higher baseline serum ALP, higher performance status (PS), or gastric cancer were at higher risk for developing hypocalcemia. The cut-off value for ALP to predict denosumab-related hypocalcemia was 587 U/L with a sensitivity of 0.77 and a specificity of 0.81. Close monitoring of serum calcium, especially after the first treatment with denosumab, is strongly recommended in these patients.

X-Linked Hypophosphatemia and FGF23-Related Hypophosphatemic Diseases: Prospect for New Treatment

Phosphate plays essential roles in many biological processes, and the serum phosphate level is tightly controlled. Chronic hypophosphatemia causes impaired mineralization of the bone matrix and results in rickets and osteomalacia. Fibroblast growth factor 23 (FGF23) is a bone-derived hormone that regulates phosphate metabolism. FGF23 excess induces hypophosphatemia via impaired phosphate reabsorption in the renal proximal tubules and decreased phosphate absorption in the intestines. There are several types of genetic and acquired FGF23-related hypophosphatemic diseases. Among these diseases, X-linked hypophosphatemia (XLH), which is caused by inactivating mutations in the phosphate-regulating endopeptidase homolog, X-linked (PHEX) gene, is the most prevalent form of genetic FGF23-related hypophosphatemic rickets. Another clinically relevant form of FGF23-related hypophosphatemic disease is tumor-induced osteomalacia (TIO), a paraneoplastic syndrome associated with FGF23-producing tumors. A combination of active vitamin D and phosphate salts is the current medical therapy used to treat patients with XLH and inoperative TIO. However, this therapy has certain efficacy- and safety-associated limitations. Several measures to inhibit FGF23 activity have been considered as possible new treatments for FGF23-related hypophosphatemic diseases. In particular, a humanized monoclonal antibody for FGF23 (burosumab) is a promising treatment in patients with XLH and TIO. This review will focus on the phosphate metabolism and the pathogenesis and treatment of FGF23-related hypophosphatemic diseases.

Prevalence and clinical outcomes of hip fractures and subchondral insufficiency fractures of the femoral head in patients with tumour-induced osteomalacia

PurposeTumour-induced osteomalacia (TIO) is a rare paraneoplastic syndrome usually caused by phosphaturic mesenchymal tumours, leading to great distress due to bone pain and affecting quality of life (QoL). This study aimed to investigate the prevalence and clinical outcomes of hip fractures and subchondral insufficiency fractures (SIF) of the femoral head.MethodsTwelve TIO patients were treated between January 2000 and December 2016 at our hospital. All underwent surgery for the tumour causing TIO, and complete removal of the tumour was accomplished in nine of 12 cases. Plain radiographs of the hip were obtained in all cases, and magnetic resonance imaging (MRI) was obtained from 15 hips representing eight patients before tumour removal. We evaluated the prevalence of hip fractures or SIF and their clinical outcomes.ResultsHip fractures were observed in six of 12 cases, and the total number of fractures was nine, of which five were femoral neck, two were intertrochanteric and two were subtrochanteric fractures. Conservative treatment, regardless of complete remission of TIO, was successful except in one case with impending subtrochanteric fracture. SIFs were observed in 11 of 24 hips. Seven of 11 hips with SIF showed progression after surgery for tumour resection.ConclusionsHip fractures and SIF are highly prevalent in TIO patients. Surgical and medical treatment for TIO is sufficient for treating hip fractures conservatively. However, SIF tends to show progression of femoral head collapse, serving as the main cause of pain after successful TIO treatment.