Daisuke Harada

FGFR3-related dwarfism and cell signaling

Skeletal development consists of the following steps: skeletal patterning, mesenchymal differentiation, bone growth, and homeostasis. In the early phase of embryogenesis, immature mesenchymal cells gather in the proper position, and the anteroposterior and dorsoventral axes are determined. This ‘‘skeletal patterning’’ is followed by ‘‘differentiation’’ of immature mesenchymal cells to chondrocytes or osteoblasts. In the appendicular skeleton, endochondral ossification takes part in elongation, and chondrocytes create the growth plate, a chondrocytic layer, and proliferate with high frequency in the longitudinal direction. Bone growth continues until the growth plate is closed at the time of pubertal maturation. In mature bones, a homeostasis process called bone remodeling occurs. Bone remodeling always renews old bone tissue by forming both osteoblasts and resorbing osteoclasts. Many essential genetic mechanisms for these bonegrowing steps have been described. Disorders of each bone formation step cause characteristic skeletal dysplasias. For example, polydactyly and split-hand are caused by patterning failure, dwarfism is caused by extraordinary differentiation and proliferation of chondrocytes in the growth plate, and osteoporosis and osteopetrosis are caused by abnormality of bone remodeling. Many functional genes are identified through genetic disorders of the skeleton and knockout mice. Skeletal disorders have been classified based on the responsible genes [1], clinical features [2], and molecular pathology and embryology [3]. According to the reviews, a total of 271 clinically different disorders and 75 responsible genes have been described. The most frequent genetic skeletal dysplasia is achondroplasia (ACH) (OMIM; #100800), caused by point mutations in the fibroblast growth factor receptor 3 (FGFR3; OMIM *134934) gene [4, 5]. Some other skeletal dysplasias are also caused by mutations located in the FGFR3, such as hypochondroplasia (HCH) (OMIM; #146000), thanatophoric dysplasia type I (TDI) (OMIM; #187600) and type II (TDII) (OMIM; #187601), and severe achondroplasia with developmental delay and acanthosis nigricans (SADDAN) (description in OMIM *134934.0015) [6–11]. The location of each mutation is unique. The phenotypes of those FGFR3-related skeletal dysplasias are similar to that of ACH, but the severity is quite different. Mutations of the FGFR3 gene have been reported to be responsible for craniofacial disorders and multiple myeloma, which are not a focus in this review. Many reports state all mutant FGFR3s are constitutively activated. Excessive D. Harada is a recepient of JSBMR Encouragement Award of 2004.

A case of autosomal dominant osteopetrosis type II with a novel TCIRG1 gene mutation

Abstract Osteopetrosis is a rare genetic disorder characterized by increased bone mineral density (BMD) due to osteoclast failure. T-cell immune regulator 1 (TCIRG1) plays crucial roles on osteoclast function, and its mutation causes autosomal recessive osteopetorosis. However, mutations in TCIRG1 have never been identified in autosomal dominant osteopetrosis (ADO). A 3-year-old boy was first presented to the clinic because of spontaneous radius and femur fractures. He has optic atrophy. The areal BMD at the lumbar spine was 1274 g/cm2 (233% of normal). Laboratory tests revealed no remarkable abnormal findings, including anemia, except for extremely elevated serum tartrate-resistant acid phosphatase-5b (14,600 mU/dL). Radiographically, the skull base, pelvis, and vertebrae showed a focal sclerosis. Genetic analysis revealed a novel de novo heterozygous missense mutation (His242Arg). Taken together with the mutation, his mild clinical features were diagnosed as ADO. This case implies that TCIRG1 could become a genetic candidate for ADO in addition to malignant forms such as ARO.

Reliability of a rapid test for the clinical diagnosis of influenza A/H1N1 2009

Abstract Background: The rapid diagnosis of a pandemic influenza A/H1N1 2009 (H1N1pdm) virus infection is required in ambulatory care settings, since early identification can prevent further transmission. However, the sensitivity of rapid influenza diagnostic tests (RIDTs) is still questionable, and specific indicators for H1N1pdm and/or false-negative results by RIDTs have not been clearly determined.Methods: From June to December 2009, nasal swabs from 324 patients at Kochi Health Science Center were used for the diagnosis of infection by RIDT and reverse transcription polymerase chain reaction. Results: The sensitivity of the RIDT was determined to be 80.0% and the specificity 97.1%. Multivariate analysis revealed that the frequencies of contagiousness and headache were significant in patients with H1N1pdm infection, in addition to common symptoms of respiratory infection. These data indicated that the H1N1pdm virus had high infectivity and was harmful to the endocranial environment. In the false-negative group, the time interval between onset and consultation was 5.5±6.5 h (median ± interquartile range), which was significantly shorter than the 11.5±7.0 h in the true-positive group. The sensitivity of the RIDT was significantly low during the time-period within 3 h from onset (56.0%); however after 4 h the sensitivity was determined to be >80%. These data indicated that the concentration of the virus in nasal swabs was elevated over the course of the disease. Conclusions: We have demonstrated that the RIDT is reliable for the diagnosis of H1N1pdm infection. Taking into consideration the time interval between onset and consultation and other features of H1N1pdm, such as contagiousness and headache, it may be necessary to re-test RIDT-negative cases later.

A case of perinatal hypophosphatasia with a novel mutation in the ALPL gene: Clinical course and review of the literature

Abstract. Hypophosphatasia (HPP) is a metabolic bone disease characterized by failure of bone calcification and vitamin B6 dependent seizures. It is caused by loss-of-function mutations in the ALPL gene. A newborn girl required respiratory support by nasal-directional positive airway pressure at birth, and pyridoxine hydrochloride administration for vitamin B6-dependent seizures observed from day two. Umbilical cord blood showed low alkaline phosphatase (ALP) activity and high pyridoxal phosphate levels. Radiographs showed severe rickets-like appearance of the bones. Genetic analysis of the ALPL gene revealed compound heterozygous mutations, c.1559delT/p.Ser188Pro. We diagnosed her with perinatal severe HPP, and started the patient on asfotase alfa from day six. Following enzyme replacement therapy (ERT), skeletal mineralization and respiratory insufficiency improved with no remarkable side-effects. Crying vital capacity (CVC) was used to evaluate respiratory status, which continuously improved from 13.3 mL/kg (day 22) to 20.6 mL/kg (day 113). Since no seizures occurred, pyridoxine hydrochloride was tapered off at one year of age. Strategies to manage perinatal severe HPP cases following ERT have not been established till date. A review of the literature shows that CVC may be a good indicator for weaning from ventilatory support. In addition, ERT will most likely enable withdrawal of pyridoxine treatment.

First-in-Asian Phase I Study of the Anti-Fibroblast Growth Factor 23 Monoclonal Antibody, Burosumab: Safety and Pharmacodynamics in Adults With X-linked Hypophosphatemia: FIRST-IN-ASIAN PHASE I STUDY OF BUROSUMAB, ANTI-FGF23 ANTIBODY

X‐linked hypophosphatemia (XLH) is a disease caused by abnormally elevated FGF23 levels, which cause persistent hypophosphatemia accompanied by subsequent reduction in bone mineralization that presents as rickets or osteomalacia. Burosumab is a fully human monoclonal antibody targeting FGF23 that is under development for the treatment of FGF23‐related hypophosphatemia including XLH. The safety, tolerability, and proof of concept of burosumab have been evaluated in patients with XLH in previous studies conducted in countries outside of Asia. The objective of this study was to evaluate the safety, tolerability, pharmacokinetics (PK), pharmacodynamics (PD), and expression of anti‐drug antibodies in Japanese and Korean adults with XLH. This was a multicenter, sequential dose‐escalation, open‐label, single‐dose study. This study began with cohort 1 (s.c. dose of burosumab 0.3 mg/kg), after which the dose was escalated sequentially in cohort 2 (s.c. dose of burosumab 0.6 mg/kg) and cohort 3 (s.c. dose of burosumab 1.0 mg/kg). The PK of burosumab were linear within the dose range of 0.3 to 1.0 mg/kg. The PD effects such as serum phosphorus concentration, serum 1,25[OH]2D3 concentration, and ratio of tubular maximum reabsorption rate of phosphate to glomerular filtration rate (TmP/GFR) were elevated after a single s.c. administration. The area under the receiver‐operating characteristic curve from 0 to t (AUC0–t) values calculated using the change from baseline values of serum phosphorus, serum 1,25(OH)2D3, and TmP/GFR were correlated with the AUC0–t of burosumab. Furthermore, no serious adverse events (AEs), deaths, remarkable increase or decrease in the corrected calcium or intact PTH levels, or signs of nephrocalcinosis or its worsening were observed after treatment. Some AEs and drug‐related AEs were observed; however, there were no clinically meaningful tendencies. The positive effects and acceptable safety profile seen in this study are encouraging for Japanese and Korean patients with XLH.

Growth Hormone and Bone

Human growth hormone (GH) is a peptide hormone physiologically secreted in the anterior pituitary gland. GH is well known to affect linear height growth. GH treatment for its effect of growth in patients with many types of disorders of short stature has been expanding. In childhood, longitudinal bones become thick at the same time as long axis elongation, and bone quantity and bone mineral density (BMD) are elevated continuously until the adolescent stage. Because patients with GH deficiency have a short stature and relatively low BMD, GH likely plays a critical role in bone mineral metabolism. To improve linear growth and bone mineral metabolism, some recent studies have challenged GH treatment in patients with metabolic bone diseases, in addition to approved diseases. In this chapter, we describe the physiology of GH action, efficacy, and trials of GH treatment. The especially on bone mineral metabolism.