Family analysis and literature study of hereditary hypophosphatemic rickets with hypercalciuria.

BACKGROUND: Hereditary hypophosphatemia rickets with hypercalciuria (HHRH) is a rare autosomal recessive disorder characterised by reduced renal phosphate reabsorption leading to hypophosphataemia, rickets and bone pain. Here, we present a case of HHRH in a Chinese boy. CASE PRESENTATION: We report a 11-year-old female proband, who was admitted to our hospital with bilateral genuvarum deformity and short stature. Computed Tomography (CT) showed kidney stones, blood tests showed hypophosphatemia, For a clear diagnosis, we employed high-throughput sequencing technology to screen for variants. Our gene sequencing approach encompassed whole exome sequencing, detection of exon and intron junction regions, and examination of a 20 bp region of adjacent introns. Flanking sequences are defined as ±50 bp upstream and downstream of the 5' and 3' ends of the coding region.The raw sequence data were compared to the known gene sequence data in publicly available sequence data bases using Burrows-Wheeler Aligner software (BWA, 0.7.12-r1039), and the pathogenic variant sites were annotated using Annovar. Subsequently, the suspected pathogenic variants were classified according to ACMG's gene variation classification system. Simultaneously, unreported or clinically ambiguous pathogenic variants were predicted and annotated based on population databases. Any suspected pathogenic variants identified through this analysis were then validated using Sanger sequencing technology. At last, the proband and her affected sister carried pathogenic homozygous variant in the geneSLC34A3(exon 13, c.1402C > T; p.R468W). Their parents were both heterozygous carriers of the variant. Genetic testing revealed that the patient has anLRP5(exon 18, c.3917C > T; p.A1306V) variant of Uncertain significance, which is a rare homozygous variant. CONCLUSION: This case report aims to raise awareness of the presenting characteristics of HHRH. The paper describes a unique case involving variants in both theSLC34A3andLRP5genes, which are inherited in an autosomal recessive manner. This combination of gene variants has not been previously reported in the literature. It is uncertain whether the presence of these two mutated genes in the same individual will result in more severe clinical symptoms. This report shows that an accurate diagnosis is critical, and with early diagnosis and correct treatment, patients will have a better prognosis.

Complex intrinsic abnormalities in osteoblast lineage cells of X-linked hypophosphatemia: Analysis of human iPS cell models generated by CRISPR/Cas9-mediated gene ablation.

X-linked hypophosphatemia (XLH) is caused by inactivating variants of the phosphate regulating endopeptidase homolog X-linked (PHEX) gene. Although the overproduction of fibroblast growth factor 23 (FGF23) is responsible for hypophosphatemia and impaired vitamin D metabolism, the pathogenesis of XLH remains unclear. We herein generated PHEX-knockout (KO) human induced pluripotent stem (iPS) cells by applying CRISPR/Cas9-mediated gene ablation to an iPS clone derived from a healthy male, and analyzed PHEX-KO iPS cells with deletions extending from exons 1 to 3 and frameshifts by inducing them to differentiate into the osteoblast lineage. We confirmed the increased production of FGF23 in osteoblast lineage cells differentiated from PHEX-KO iPS cells. In vitro mineralization was enhanced in osteoblast lineage cells from PHEX-KO iPS cells than in those from isogenic control iPS cells, which reminded us of high bone mineral density and enthesopathy in patients with XLH. The extracellular level of pyrophosphate (PPi), an inhibitor of mineralization, was elevated, and this increase appeared to be partly due to the reduced activity of tissue non-specific alkaline phosphatase (TNSALP). Osteoblast lineage cells derived from PHEX-KO iPS cells also showed the increased expression of multiple molecules such as dentine matrix protein 1, osteopontin, RUNX2, FGF receptor 1 and early growth response 1. This gene dysregulation was similar to that in the osteoblasts/osteocytes of Phex-deficient Hyp mice, suggesting that common pathogenic mechanisms are shared between human XLH and Hyp mice. Moreover, we found that the phosphorylation of CREB was markedly enhanced in osteoblast lineage cells derived from PHEX-KO iPS cells, which appeared to be associated with the up-regulation of the parathyroid hormone related protein gene. PHEX deficiency also affected the response of the ALPL gene encoding TNSALP to extracellular Pi. Collectively, these results indicate that complex intrinsic abnormalities in osteoblasts/osteocytes underlie the pathogenesis of human XLH.

Disease Manifestations and Complications in Dutch X-Linked Hypophosphatemia Patients.

X-linked hypophosphatemia (XLH) is the most common monogenetic cause of chronic hypophosphatemia, characterized by rickets and osteomalacia. Disease manifestations and treatment of XLH patients in the Netherlands are currently unknown. Characteristics of XLH patients participating in the Dutch observational registry for genetic hypophosphatemia and acquired renal phosphate wasting were analyzed. Eighty XLH patients, including 29 children, were included. Genetic testing, performed in 78.8% of patients, showed a PHEX mutation in 96.8%. Median (range) Z-score for height was - 2.5 (- 5.5; 1.0) in adults and - 1.4 (- 3.7; 1.0) in children. Many patients were overweight or obese: 64.3% of adults and 37.0% of children. All children received XLH-related medication e.g., active vitamin D, phosphate supplementation or burosumab, while 8 adults used no medication. Lower age at start of XLH-related treatment was associated with higher height at inclusion. Hearing loss was reported in 6.9% of children and 31.4% of adults. Knee deformities were observed in 75.0% of all patients and osteoarthritis in 51.0% of adult patients. Nephrocalcinosis was observed in 62.1% of children and 33.3% of adults. Earlier start of XLH-related treatment was associated with higher risk of nephrocalcinosis and detection at younger age. Hyperparathyroidism longer than six months was reported in 37.9% of children and 35.3% of adults. This nationwide study confirms the high prevalence of adiposity, hearing loss, bone deformities, osteoarthritis, nephrocalcinosis and hyperparathyroidism in Dutch XLH patients. Early start of XLH-related treatment appears to be beneficial for longitudinal growth but may increase development of nephrocalcinosis.

Latin-American consensus on the transition into adult life of patients with X-linked hypophosphatemia.

INTRODUCTION: X-linked hypophosphatemia is an orphan disease of genetic origin and multisystem involvement. It is characterized by a mutation of the PHEX gene which results in excess FGF23 production, with abnormal renal and intestinal phosphorus metabolism, hypophosphatemia and osteomalacia secondary to chronic renal excretion of phosphate. Clinical manifestations include hypophosphatemic rickets leading to growth abnormalities and osteomalacia, myopathy, bone pain and dental abscesses. The transition of these patients to adult life continues to pose challenges to health systems, medical practitioners, patients and families. For this reason, the aim of this consensus is to provide a set of recommendations to facilitate this process and ensure adequate management and follow-up, as well as the quality of life for patients with X-linked hypophosphatemia as they transition to adult life. MATERIALS AND METHODS: Eight Latin American experts on the subject participated in the consensus and two of them were appointed as coordinators. The consensus work was done in accordance with the nominal group technique in 6 phases: (1) question standardization, (2) definition of the maximum number of choices, (3) production of individual solutions or answers, (4) individual question review, (5) analysis and synthesis of the information and (6) synchronic meetings for clarification and voting. An agreement was determined to exist with 80% votes in favor in three voting cycles. RESULTS AND DISCUSSION: Transition to adult life in patients with hypophosphatemia is a complex process that requires a comprehensive approach, taking into consideration medical interventions and associated care, but also the psychosocial components of adult life and the participation of multiple stakeholders to ensure a successful process. The consensus proposes a total of 33 recommendations based on the evidence and the knowledge and experience of the experts. The goal of the recommendations is to optimize the management of these patients during their transition to adulthood, bearing in mind the need for multidisciplinary management, as well as the most relevant medical and psychosocial factors in the region.

FGF23 directly inhibits osteoprogenitor differentiation in Dmp1-knockout mice.

Fibroblast growth factor 23 (FGF23) is a phosphate-regulating (Pi-regulating) hormone produced by bone. Hereditary hypophosphatemic disorders are associated with FGF23 excess, impaired skeletal growth, and osteomalacia. Blocking FGF23 became an effective therapeutic strategy in X-linked hypophosphatemia, but testing remains limited in autosomal recessive hypophosphatemic rickets (ARHR). This study investigates the effects of Pi repletion and bone-specific deletion of Fgf23 on bone and mineral metabolism in the dentin matrix protein 1-knockout (Dmp1KO) mouse model of ARHR. At 12 weeks, Dmp1KO mice showed increased serum FGF23 and parathyroid hormone levels, hypophosphatemia, impaired growth, rickets, and osteomalacia. Six weeks of dietary Pi supplementation exacerbated FGF23 production, hyperparathyroidism, renal Pi excretion, and osteomalacia. In contrast, osteocyte-specific deletion of Fgf23 resulted in a partial correction of FGF23 excess, which was sufficient to fully restore serum Pi levels but only partially corrected the bone phenotype. In vitro, we show that FGF23 directly impaired osteoprogenitors' differentiation and that DMP1 deficiency contributed to impaired mineralization independent of FGF23 or Pi levels. In conclusion, FGF23-induced hypophosphatemia is only partially responsible for the bone defects observed in Dmp1KO mice. Our data suggest that combined DMP1 repletion and FGF23 blockade could effectively correct ARHR-associated mineral and bone disorders.

X-Linked Familial Hypophosphatemia: A Case Report of 27-Year Old Male and Review of Literature.

X-linked hypophosphatemia (XLH) associated with short stature during childhood are mostly referred to the hospital and diagnosed as vitamin D deficiency rickets and received vitamin D before adulthood. A case is presented with clinical features of hypophosphatemia from childhood who did not seek medical care for diagnosis and treatment, nor did his mother or two brothers, who have short statures, bone pain, and fractures. The patient was assessed for sociodemographic, hematological, and biochemical parameters together with a genetic assessment. A DEXA scan and X-ray were done to determine the abnormalities and deformities of joints and bones despite clinical examination by an expert physician. All imaging, laboratory parameters, and the genetic study confirmed the diagnosis of XLH. A detailed follow-up of his condition was performed after the use of phosphate tablets and other treatments. X-linked hypophosphatemia needs a good assessment, care, and follow up through a complementary medical team including several specialties. Phosphate tablets in adulthood significantly affects clinical and physical improvement and prevention of further skeletal abnormality and burden on daily activity. The patients should be maintained with an adequate dose of phosphate for better patient compliance. More awareness is needed in society and for health professionals when conducting medical checkups during the presence of stress fractures, frequent dental and gum problems, rickets, short stature, or abnormality in the skeleton or walking to think of secondary causes such as hypophosphatemia. Further investigations including a visit to a specialist is imperative to check for the primary cause of these disturbances.

Adult height improved over decades in patients with X-linked hypophosphatemia: a cohort study.

OBJECTIVES: The aim of this study is to analyze height after cessation of growth (final height [FH]) and its evolution over the last decades in X-linked hypophosphatemia (XLH) patients in France, as the data on natural history of FH in XLH are lacking. DESIGN: We performed a retrospective observational study in a large cohort of French XLH patients with available data on FH measurements. MATERIALS AND METHODS: We divided patients into 3 groups according to their birth year: group 1 born between 1950 and 1974, group 2 born between 1975 and 2000, and group 3 born between 2001 and 2006, respectively, and compared their FHs. RESULTS: A total of 398 patients were included. Mean FHs were the following: for group 1, -2.31 ± 1.11 standard deviation score (SDS) (n = 127), 156.3 ± 9.7 cm in men and 148.6 ± 6.5 cm in women; for group 2, -1.63 ± 1.13 SDS (n = 193), 161.6 ± 8.5 cm in men and 153.1 ± 7.2 cm in women; and for group 3, -1.34 ± 0.87 SDS (n = 78), 165.1 ± 5.5 cm in men and 154.7 ± 6 cm in women. We report a significant increase in mean FH SDS over 3 generations of patients, for both men and women (P < .001). Final height SDS in male (-2.08 ± 1.18) was lower than in female (-1.70 ± 1.12) (P = .002). CONCLUSION: The FH of XLH patients in France increased significantly over the last decades. Even though men's FHs improved more than women's, men with XLH remain shorter reflecting a more severe disease phenotype. While the results are promising, most patients with XLH remain short leaving room for improvement.

Mutations of family with sequence similarity 20-member C gene causing lethal and nonlethal Raine syndrome causes hypophosphatemia rickets.

Family with sequence similarity 20-member C (FAM20C) is a kinase specific to most of the secreted phosphoproteome. FAM20C has been identified as the causative gene of Raine syndrome, initially characterized by lethal osteosclerosis bone dysplasia. However, since the identification of the cases of nonlethal Raine syndrome characterized by hypophosphatemia rickets, the previous definition of Raine syndrome has become debatable and raised a question about the role of mutations of FAM20C in controversial skeletal manifestation in the two forms of the disease. In this study, we aimed to investigate the influence of FAM20C mutations on skeletogenesis. We developed transgenic mice expressing Fam20c mutations mimicking those associated with human lethal and nonlethal Raine syndrome. The results revealed that transgenic mice expressing the mutant Fam20c found in the lethal (KO;G374R) and nonlethal (KO;D446N) Raine syndrome exhibited osteomalacia without osteosclerotic features. Additionally, both mutants significantly increased the expression of the Fgf23, indicating that Fam20c deficiency in skeletal compartments causes hypophosphatemia rickets. Furthermore, as FAM20C kinase activity catalyzes the phosphorylation of secreted proteomes other than those in the skeletal system, global FAM20C deficiency may trigger alterations in other systems resulting in osteosclerosis secondary to hypophosphatemia rickets. Together, the findings of this study suggest that FAM20C deficiency primarily causes hypophosphatemia rickets or osteomalacia; however, the heterogeneous skeletal manifestation in Raine syndrome was not determined solely by specific mutations of FAM20C. The findings also implicated that rickets or osteomalacia caused by FAM20C deficiency would deteriorate into osteosclerosis by the defects from other systems or environmental impacts.

X-linked hypophosphatemia caused by a deep intronic variant in PHEX identified by PCR-based RNA analysis of urine-derived cells.

X-linked hypophosphatemia (XLH) is caused by dominant inactivating mutations in the phosphate regulating endopeptidase homology, X-linked (PHEX), resulting in elevated fibroblast growth factor 23 (FGF23), hypophosphatemia, rickets and osteomalacia. PHEX variants are identified in approximately 85 % of individuals with XLH, which leaves a substantial proportion of patients with negative DNA-based genetic testing. Here we describe a 16-year-old male who had typical features of XLH on clinical and radiological examination. Genomic DNA sequencing of a hypophosphatemia gene panel did not reveal a pathogenic variant. We therefore obtained a urine sample, established cell cultures and obtained PHEX cDNA from urine-derived cells. Sequencing of exon-spanning PCR products demonstrated the presence of an 84 bp pseudoexon in PHEX intron 21 due to a deep intronic variant (c.2147+1197A>G), which created a new splice donor site in intron 21. The corresponding PHEX protein would lack 33 amino acids on the C-terminus and instead include an unrelated sequence of 17 amino acids. The patient and his affected mother both had this variant. This report highlights that individuals with the typical clinical characteristics of XLH and negative genomic DNA sequence analysis can have deep intronic PHEX variants that are detectable by PCR-based RNA diagnostics.

X-linked hypophosphatemia in 4 generations due to an exon 13-15 duplication in PHEX, in the absence of the c.*231A>G variant.

X-linked hypophosphatemia is the most common cause of inherited rickets, due to inactivating variants of PHEX. More than 800 variants have been described to date and one which consists of a single base change in the 3' untranslated region (UTR) (c.*231A>G) is reported as prevalent in North America. Recently an exon 13-15 duplication has been found to occur in concert with the c.*231A>G variant, and thus it is unclear whether the pathogenicity is solely a function of the UTR variant. We present a family with XLH who harbors the exon 13-15 duplication but does not carry the 3'UTR variant, providing evidence that the duplication itself is the pathogenic variant when these two variants are found in cis.

Murine models of HRAS-mediated cutaneous skeletal hypophosphatemia syndrome suggest bone as the FGF23 excess source.

Cutaneous skeletal hypophosphatemia syndrome (CSHS) is a mosaic RASopathy characterized by the association of dysplastic skeletal lesions, congenital skin nevi of epidermal and/or melanocytic origin, and FGF23-mediated hypophosphatemia. The primary physiological source of circulating FGF23 is bone cells. However, several reports have suggested skin lesions as the source of excess FGF23 in CSHS. Consequently, without convincing evidence of efficacy, many patients with CSHS have undergone painful removal of cutaneous lesions in an effort to normalize blood phosphate levels. This study aims to elucidate whether the source of FGF23 excess in CSHS is RAS mutation-bearing bone or skin lesions. Toward this end, we analyzed the expression and activity of Fgf23 in two mouse models expressing similar HRAS/Hras activating mutations in a mosaic-like fashion in either bone or epidermal tissue. We found that HRAS hyperactivity in bone, not skin, caused excess of bioactive intact FGF23, hypophosphatemia, and osteomalacia. Our findings support RAS-mutated dysplastic bone as the primary source of physiologically active FGF23 excess in patients with CSHS. This evidence informs the care of patients with CSHS, arguing against the practice of nevi removal to decrease circulating, physiologically active FGF23.

Uncovering genetic causes of hypophosphatemia.

BACKGROUND: Chronic hypophosphatemia can result from a variety of acquired disorders, such as malnutrition, intestinal malabsorption, hyperparathyroidism, vitamin D deficiency, excess alcohol intake, some drugs, or organ transplantation. Genetic disorders can be a cause of persistent hypophosphatemia, although they are less recognized. We aimed to better understand the prevalence of genetic hypophosphatemia in the population. METHODS: By combining retrospective and prospective strategies, we searched the laboratory database of 815,828 phosphorus analyses and included patients 17-55 years old with low serum phosphorus. We reviewed the charts of 1287 outpatients with at least 1 phosphorus result ≤2.2 mg/dL. After ruling out clear secondary causes, 109 patients underwent further clinical and analytical studies. Among them, we confirmed hypophosphatemia in 39 patients. After excluding other evident secondary causes, such as primary hyperparathyroidism and vitamin D deficiency, we performed a molecular analysis in 42 patients by sequencing the exonic and flanking intronic regions of a panel of genes related to rickets or hypophosphatemia (CLCN5, CYP27B1, dentin matrix acidic phosphoprotein 1, ENPP1, FAM20C, FGFR1, FGF23, GNAS, PHEX, SLC34A3, and VDR). RESULTS: We identified 14 index patients with hypophosphatemia and variants in genes related to phosphate metabolism. The phenotype of most patients was mild, but two patients with X-linked hypophosphatemia (XLH) due to novel PHEX mutations had marked skeletal abnormalities. CONCLUSION: Genetic causes should be considered in children, but also in adult patients with hypophosphatemia of unknown origin. Our data are consistent with the conception that XLH is the most common cause of genetic hypophosphatemia with an overt musculoskeletal phenotype.

Successful treatment with MEK-inhibitor in a patient with NRAS-related cutaneous skeletal hypophosphatemia syndrome.

Cutaneous skeletal hypophosphatemia syndrome (CSHS) is caused by somatic mosaic NRAS variants and characterized by melanocytic/sebaceous naevi, eye, and brain malformations, and FGF23-mediated hypophosphatemic rickets. The MEK inhibitor Trametinib, acting on the RAS/MAPK pathway, is a candidate for CSHS therapy. A 4-year-old boy with seborrheic nevus, eye choristoma, multiple hamartomas, brain malformation, pleural lymphangioma and chylothorax developed severe hypophosphatemic rickets unresponsive to phosphate supplementation. The c.182A > G;p.(Gln61Arg) somatic NRAS variant found in DNA from nevus biopsy allowed diagnosing CSHS. We administered Trametinib for 15 months investigating the transcriptional effects at different time points by whole blood RNA-seq. Treatment resulted in prompt normalization of phosphatemia and phosphaturia, catch-up growth, chylothorax regression, improvement of bone mineral density, reduction of epidermal nevus and hamartomas. Global RNA sequencing on peripheral blood mononucleate cells showed transcriptional changes under MEK inhibition consisting in a strong sustained downregulation of signatures related to RAS/MAPK, PI3 kinase, WNT and YAP/TAZ pathways, reverting previously defined transcriptomic signatures. CSHS was effectively treated with a MEK inhibitor with almost complete recovery of rickets and partial regression of the phenotype. We identified "core" genes modulated by MEK inhibition potentially serving as surrogate markers of Trametinib action.

Genetic analysis combined with 3D-printing assistant surgery in diagnosis and treatment for an X-linked hypophosphatemia patient.

BACKGROUND: Hypophosphatemia is mainly characterized by hypophosphatemia and a low level of 1alpha,25-Dihydroxyvitamin D2 (1,25-(OH)2 D2) and/or 1alpha,25-Dihydroxyvitamin D3 (1,25-(OH)2 D3) in the blood. Previous studies have demonstrated that variants in PHEX and FGF23 are primarily responsible for this disease. Although patients with variants of these two genes share almost the same symptoms, they exhibit the different hereditary pattern, X-link dominant and autosome dominant, respectively. Three-dimensional (3D) printing is a method which can accurately reconstruct physical objects, and its applications in orthopedics can contribute to realizing a more accurate surgical performance and a better outcome. METHODS: An X-linked hypophosphatemia (XLH) family was recruited, with four patients across three generations. We screened candidate genes and filtered a duplication variant in PHEX. Variant analysis and co-segregation confirmation were then performed. Before the operation of our patient, a digital model of our patient's leg had been rebuilt upon the CT scan data, and a polylactic acid (PLA) model had been 3D-printed. RESULTS: A novel duplication PHEX variant c.574dupG (p.A192GfsX20) was identified in a family with XLH. Its pathogenicity was confirmed by the co-segregation assay and online bioinformatics database. The preoperative plan was made with the help of the PLA model. Then, arch osteotomy and transverse osteotomy were performed under the guidance of the previous simulation. The appearance of the surgical-intervened leg was satisfactory. CONCLUSIONS: This study identified a novel PHEX variant and showed that 3D printing tech is a very promising approach for corrective osteotomies.

Novel PHEX gene locus-specific database: Comprehensive characterization of vast number of variants associated with X-linked hypophosphatemia (XLH).

X-linked hypophosphatemia (XLH), the most common form of hereditary hypophosphatemia, is caused by disrupting variants in the PHEX gene, located on the X chromosome. XLH is inherited in an X-linked pattern with complete penetrance observed for both males and females. Patients experience lifelong symptoms resulting from chronic hypophosphatemia, including impaired bone mineralization, skeletal deformities, growth retardation, and diminished quality of life. This chronic condition requires life-long management with disease-specific therapies, which can improve patient outcomes especially when initiated early in life. To centralize and disseminate PHEX variant information, we have established a new PHEX gene locus-specific database, PHEX LSDB. As of April 30, 2021, 870 unique PHEX variants, compiled from an older database of PHEX variants, a comprehensive literature search, a sponsored genetic testing program, and XLH clinical trials, are represented in the PHEX LSDB. This resource is publicly available on an interactive, searchable website (https://www.rarediseasegenes.com/), which includes a table of variants and associated data, graphical/tabular outputs of genotype-phenotype analyses, and an online submission form for reporting new PHEX variants. The database will be updated regularly with new variants submitted on the website, identified in the published literature, or shared from genetic testing programs.

Clinical, biochemical and genetic findings in adult patients with chronic hypophosphatasemia.

PURPOSE: The study aimed to define the clinical, biochemical and genetic features of adult patients with osteopenia/osteoporosis and/or bone fragility and low serum alkaline phosphatase (sALP). METHODS: Twenty-two patients with at least two sALP values below the reference range were retrospectively enrolled after exclusion of secondary causes. Data about clinical features, mineral and bone markers, serum pyridoxal-5'-phosphate (PLP), urine phosphoethanolamine (PEA), lumbar and femur bone densitometry, and column X-ray were collected. Peripheral blood DNA of each participant was analyzed to detect ALPL gene anomalies. RESULTS: Pathogenic ALPL variants (pALPL) occurred in 23% and benign variants in 36% of patients (bALPL), while nine patients harbored wild-type alleles (wtALPL). Fragility fractures and dental anomalies were more frequent in patients harboring pALPL and bALPL than in wtALPL patients. Of note, wtALPL patients comprised women treated with tamoxifen for hormone-sensitive breast cancer. Mineral and bone markers were similar in the three groups. Mean urine PEA levels were significantly higher in patients harboring pALPL than those detected in patients harboring bALPL and wtALPL; by contrast, serum PLP levels were similar in the three groups. A 6-points score, considering clinical and biochemical features, was predictive of pALPL detection [P = 0.060, OR 1.92 (95% CI 0.972, 3.794)], and more significantly of pALPL or bALPL [P = 0.025, OR 14.33 (95% CI 1.401, 14.605)]. CONCLUSION: In osteopenic/osteoporotic patients, single clinical or biochemical factors did not distinguish hypophosphatasemic patients harboring pALPL or bALPL from those harboring wtALPL. Occurrence of multiple clinical and biochemical features is predictive of ALPL anomalies, and, therefore, they should be carefully identified. Tamoxifen emerged as a hypophosphatasemic drug.

Molecular Diagnoses of X-Linked and Other Genetic Hypophosphatemias: Results From a Sponsored Genetic Testing Program.

X-linked hypophosphatemia (XLH), a dominant disorder caused by pathogenic variants in the PHEX gene, affects both sexes of all ages and results in elevated serum fibroblast growth factor 23 (FGF23) and below-normal serum phosphate. In XLH, rickets, osteomalacia, short stature, and lower limb deformity may be present with muscle pain and/or weakness/fatigue, bone pain, joint pain/stiffness, hearing difficulty, enthesopathy, osteoarthritis, and dental abscesses. Invitae and Ultragenyx collaborated to provide a no-charge sponsored testing program using a 13-gene next-generation sequencing panel to confirm clinical XLH or aid diagnosis of suspected XLH/other genetic hypophosphatemia. Individuals aged ≥6 months with clinical XLH or suspected genetic hypophosphatemia were eligible. Of 831 unrelated individuals tested between February 2019 and June 2020 in this cross-sectional study, 519 (62.5%) individuals had a pathogenic or likely pathogenic variant in PHEX (PHEX-positive). Among the 312 PHEX-negative individuals, 38 received molecular diagnoses in other genes, including ALPL, CYP27B1, ENPP1, and FGF23; the remaining 274 did not have a molecular diagnosis. Among 319 patients with a provider-reported clinical diagnosis of XLH, 88.7% (n = 283) had a reportable PHEX variant; 81.5% (n = 260) were PHEX-positive. The most common variant among PHEX-positive individuals was an allele with both the gain of exons 13-15 and c.*231A>G (3'UTR variant) (n = 66/519). Importantly, over 80% of copy number variants would have been missed by traditional microarray analysis. A positive molecular diagnosis in 41 probands (4.9%; 29 PHEX positive, 12 non-PHEX positive) resulted in at least one family member receiving family testing. Additional clinical or family member information resulted in variant(s) of uncertain significance (VUS) reclassification to pathogenic/likely pathogenic (P/LP) in 48 individuals, highlighting the importance of segregation and clinical data. In one of the largest XLH genetic studies to date, 65 novel PHEX variants were identified and a high XLH diagnostic yield demonstrated broad insight into the genetic basis of XLH. © 2021 The Authors. Journal of Bone and Mineral Research published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research (ASBMR).

TNAP: A New Multitask Enzyme in Energy Metabolism.

Tissue-nonspecific alkaline phosphatase (TNAP) is mainly known for its necessary role in skeletal and dental mineralization, which relies on the hydrolysis of the mineralization inhibitor inorganic pyrophosphate (PPi). Mutations in the gene encoding TNAP leading to severe hypophosphatasia result in strongly reduced mineralization and perinatal death. Fortunately, the relatively recent development of a recombinant TNAP with a bone anchor has allowed to correct the bone defects and prolong the life of affected babies and children. Researches on TNAP must however not be slowed down, because accumulating evidence indicates that TNAP activation in individuals with metabolic syndrome (MetS) is associated with enhanced cardiovascular mortality, presumably in relation with cardiovascular calcification. On the other hand, TNAP appears to be necessary to prevent the development of steatohepatitis in mice, suggesting that TNAP plays protective roles. The aim of the present review is to highlight the known or suspected functions of TNAP in energy metabolism that may be associated with the development of MetS. The location of TNAP in liver and its function in bile excretion, lipopolysaccharide (LPS) detoxification and fatty acid transport will be presented. The expression and function of TNAP in adipocyte differentiation and thermogenesis will also be discussed. Given that TNAP is a tissue- and substrate-nonspecific phosphatase, we believe that it exerts several crucial pathophysiological functions that are just beginning to be discovered.

Consensus Recommendations for the Diagnosis and Management of X-Linked Hypophosphatemia in Belgium.

X-linked hypophosphatemia (XLH) is the most common genetic form of hypophosphatemic rickets and osteomalacia. In this disease, mutations in the PHEX gene lead to elevated levels of the hormone fibroblast growth factor 23 (FGF23), resulting in renal phosphate wasting and impaired skeletal and dental mineralization. Recently, international guidelines for the diagnosis and treatment of this condition have been published. However, more specific recommendations are needed to provide guidance at the national level, considering resource availability and health economic aspects. A national multidisciplinary group of Belgian experts convened to discuss translation of international best available evidence into locally feasible consensus recommendations. Patients with XLH may present to a wide array of primary, secondary and tertiary care physicians, among whom awareness of the disease should be raised. XLH has a very broad differential-diagnosis for which clinical features, biochemical and genetic testing in centers of expertise are recommended. Optimal care requires a multidisciplinary approach, guided by an expert in metabolic bone diseases and involving (according to the individual patient's needs) pediatric and adult medical specialties and paramedical caregivers, including but not limited to general practitioners, dentists, radiologists and orthopedic surgeons. In children with severe or refractory symptoms, FGF23 inhibition using burosumab may provide superior outcomes compared to conventional medical therapy with phosphate supplements and active vitamin D analogues. Burosumab has also demonstrated promising results in adults on certain clinical outcomes such as pseudofractures. In summary, this work outlines recommendations for clinicians and policymakers, with a vision for improving the diagnostic and therapeutic landscape for XLH patients in Belgium.