Background X-linked hypophosphatemia (XLH) is an inherited disease of phosphate metabolism in which inactivating mutations of the Phosphate Regulating Endopeptidase Homolog, X-Linked ( PHEX ) gene lead to local and systemic effects including impaired growth, rickets, osteomalacia, bone abnormalities, bone pain, spontaneous dental abscesses, hearing difficulties, enthesopathy, osteoarthritis, and muscular dysfunction. Patients with XLH present with elevated levels of fibroblast growth factor 23 (FGF23), which is thought to mediate many of the aforementioned manifestations of the disease. Elevated FGF23 has also been observed in many other diseases of hypophosphatemia, and a range of animal models have been developed to study these diseases, yet the role of FGF23 in the pathophysiology of XLH is incompletely understood. Methods The role of FGF23 in the pathophysiology of XLH is here reviewed by describing what is known about phenotypes associated with various PHEX mutations, animal models of XLH, and non-nutritional diseases of hypophosphatemia, and by presenting molecular pathways that have been proposed to contribute to manifestations of XLH. Results The pathophysiology of XLH is complex, involving a range of molecular pathways that variously contribute to different manifestations of the disease. Hypophosphatemia due to elevated FGF23 is the most obvious contributor, however localised fluctuations in tissue non-specific alkaline phosphatase (TNAP), pyrophosphate, calcitriol and direct effects of FGF23 have been observed to be associated with certain manifestations. Conclusions By describing what is known about these pathways, this review highlights key areas for future research that would contribute to the understanding and clinical treatment of non-nutritional diseases of hypophosphatemia, particularly XLH.

Objective: To estimate the incidence of nutritional rickets and the incidence and prevalence of hereditary rickets. Design: Population-based retrospective cohort study based on a review of medical records. Methods: Patients aged 0-14.9 years referred to or discharged from hospitals in southern Denmark from 1985 to 2005 with a diagnosis of rickets were identified by register search, and their medical records were retrieved. Patients fulfilling the diagnostic criteria of primary rickets were included. Results: We identified 112 patients with nutritional rickets of whom 74% were immigrants. From 1995 to 2005, the average incidence of nutritional rickets in children aged 0-14.9 and 0-2.9 years was 2.9 and 5.8 per 100 000 per year respectively. Among immigrant children born in Denmark, the average incidence was 60 (0-14.9 years) per 100 000 per year. Ethnic Danish children were only diagnosed in early childhood and the average incidence in the age group 0-2.9 years declined from 5.0 to 2.0 per 100 000 per year during 1985-1994 to 1995-2005. Sixteen cases of hereditary rickets were diagnosed during the study period giving an average incidence of 4.3 per 100 000 (0-0.9 years) per year. The prevalence of hypophosphatemic rickets and vitamin D-dependent rickets type 1 was 4.8 and 0.4 per 100 000 (0-14.9 years) respectively. Conclusions: Nutritional rickets is rare in southern Denmark and largely restricted to immigrants, but the incidence among ethnic Danish children was unexpectedly high. Hereditary rickets is the most common cause of rickets in ethnic Danish children, but nutritional rickets is most frequent among all young children.

Hypophosphatemic rickets (HR) is a group of rare disorders caused by excessive renal phosphate wasting. The purpose of this cross-sectional study of 38 HR patients was to characterize the phenotype of adult HR patients. Moreover, skeletal and endodontic severity scores were defined to assess possible gender differences in disease severity in patients with genetically verified X-linked HR. Compared to normal reference data, i.e., z = 0, HR patients had significantly lower final height, with a mean difference in z-score of -1.9 (95% CI -2.4 to -1.4, P < 0.001). Compared to paired z-scores of final height, z-scores of leg length were significantly lower and those of sitting height were significantly higher (P < 0.001), resulting in disproportion as indicated by the significantly elevated sitting height ratio, mean difference in z-score of 2.6 (95% CI 2.1-3.1, P < 0.001). Z-scores of head circumference (median 1.4, range -0.4 to 5.5, P < 0.001) and z-scores of bone mineral density (BMD) of the lumbar spine (median 1.9, range -1.5 to 8.6, P < 0.001) were significantly elevated compared to normal reference data. The relative risk (RR) of fracture was reduced (RR = 0.34, 95% CI 0.20-0.57, P < 0.001). The skeletal severity score tended to be higher in males compared to females (P = 0.07), and no gender difference in endodontic severity was found. In conclusion, adult HR patients were characterized by short stature and were disproportioned. They had elevated BMD of the lumbar spine and a reduced risk of fractures. We found a tendency for males to be more severely affected than females.

-Respiratory distress syndrome (RDS) and bronchopulmonary dysplasia (BPD) are major complications to preterm birth. Hypovitaminosis D is prevalent in pregnancy. We systematically reviewed the evidence of the impact of vitamin D on lung development, surfactant synthesis, RDS, and BPD searching PubMed, Embase, and Cochrane databases with the terms vitamin D AND (surfactant OR lung maturation OR lung development OR respiratory distress syndrome OR fetal lung OR prematurity OR bronchopulmonary dysplasia). Three human studies, ten animal studies, two laboratory studies, and one combined animal and laboratory study were included. Human evidence was sparse, allowing no conclusions. BPD was not associated with vitamin D receptor polymorphism in a fully adjusted analysis. Animal and laboratory studies showed substantial positive effects of vitamin D on the alveolar type II cell, fibroblast proliferation, surfactant synthesis, and alveolarization. These data support the hypothesis of hypovitaminosis D as a frequent, modifiable risk factor of RDS and BPD, which should be tested in randomized controlled trials on pregnant women, those with threatening preterm delivery, or in the preterm neonates. Future experimental and human studies should aim to identify optimal time windows, vitamin D doses, and cut-off levels for 25-hydroxyvitamin D in interventions against RDS, BPD, and later adverse respiratory outcomes. vitamin D; fetus; lung; surfactant; preterm; neonate THE IMPORTANCE OF VITAMIN D in nonskeletal fetal and childhood health has become increasingly recognized in the last decades (19,65). The impact of vitamin D on early lung development and maturation and lung diseases of early life is an emerging field of research. Hypovitaminosis D during pregnancy is associated with reduced placental development and weight, leading to a presumed risk of preterm birth (24,25), which per se may lead to respiratory distress syndrome (RDS) and bronchopulmonary dysplasia (BPD). Moreover, vitamin D is suggested to play a role in the embryogenesis and in cellular growth and differentiation, including lung development and regulation of lung maturation in the fetus (23,29,38,70,71,108), whereby hypovitaminosis D could be hypothesized to aggravate premature neonatal lung diseases.Vitamin D is involved in the development of the innate and adaptive immune system, and, because of its unique capacity to bind to the vitamin D receptor (VDR) and thereby to serve as a transcriptional factor, vitamin D can regulate gene expression and exert widespread immunomodulatory effects including proliferation, differentiation, and complex regulation (19, 56, 58 -61, 64, 65, 68, 69, 105). Evidence suggests that vitamin D may stimulate regulatory T cell development and T cell function to suppress inappropriate Th1 and Th2 responses to environmental exposure (i.e., allergens, infection load), leading to a more balanced immune response inhibiting autoimmune diseases (with Th1 dominance) and allergic diseases (Th2 dominance) (55). Vitamin D could therefore be inv...

Vitamin D insufficiency was widespread in early pregnancy. Associations to smoking, prepregnancy BMI and origin outside Europe varied with season. Multiparity and not being tanned in Caucasians represent new risk factors of vitamin D insufficiency.

We found an increasing prevalence of maternal chronic disease during pregnancy and more than a four-fold increased risk of maternal chronic disease during pregnancy for childbirths in the period 2009 through 2013, compared with 1989 through 1993. The main limitation of our study is related to a potentially greater awareness and hence more careful registration of maternal chronic disease over time and thereby an increased tendency to register diseases.

We found an association between 25(OH)D and first-trimester miscarriages, suggesting vitamin D as a modifiable risk factor for miscarriage. To test this hypothesis, randomized controlled trials should investigate the possible effect of vitamin D supplementation to increase 25(OH)D concentrations in early pregnancy, or before conception, to decrease risk of miscarriage. This trial was registered at clinicaltrials.gov as NCT02434900.

Background X-linked hypophosphataemia (XLH) is a rare, hereditary, progressive and lifelong phosphate wasting disorder characterised by pathological elevations in fibroblast growth factor (FGF) 23 concentration and activity; XLH has an incidence of approximately 1 in 20–25,000 individuals. Excess FGF23 activity leads to increased phosphate excretion in the kidneys – mediated by downregulation of renal tubular phosphate transporters – and reduced phosphate absorption in the intestines – due to impaired vitamin D activation. This results in impaired bone growth and mineralisation, short and disproportionate stature, leg bowing, musculoskeletal pain, spontaneous dental abscesses, rickets, and osteomalacia. The spectrum of manifestations differs between paediatric and adult patients. Those involved in the treatment of this condition face many challenges, including a lack of robust natural history and demographic data. This multicentre, international, rare-disease patient registry (XLH Registry) was established to address the paucity of data in XLH and to help inform future clinical practice. Results The XLH Registry collects standard diagnostic and monitoring practice data, including (where applicable) diagnosis and disease progression history, treatment regimens and family history; the protocol does not mandate any interventions or clinical assessments. The XLH Registry aims to recruit 1200 paediatric and adult patients with XLH over 10 years, and several data analyses and peer-reviewed publications are expected to be generated throughout this period. A post-authorisation safety study for Bburosumab, for which the registry Sponsor is the marketing authorisation holder, will be nested as a sub-study within the XLH Registry via a subsequent protocol amendment. Conclusion The data collected within this rare-disease patient registry will be utilised to synthesise real-world evidence to inform the management of XLH, to improve the quality of life and standard of care of patients living with this rare debilitating disease.