Biology of bone mineralization and ectopic calcifications: the same actors for different plays.

Bone has several crucial functions. It is essential for locomotion and allows our body to stand erect against gravity. A mismatch between the mechanical stresses applied to it and its mechanical resistance leads to fractures. Bone also has numerous endocrine functions. It acts as a reservoir for minerals such as calcium and phosphorus, making it the target of calciotropic hormones that mobilize these minerals, particularly calcium, according to the body's needs. Additionally, bone secretes hormones, notably fibroblast growth factor 23 (FGF23), which regulates urinary excretion of phosphate and the bioavailability of active vitamin D. Bone mineralization is the process that facilitates the organized deposition of minerals in the bone matrix, providing rigidity and appropriate mechanical resistance. This process is compromised in genetically related bone mineralization disorders, such as those causing hypophosphatemia or hypophosphatasia. Conversely, calcification can be pathological, affecting soft tissues like the blood vessels, as seen in generalized arterial calcification of infancy (GACI) or arterial calcification due to CD73 deficiency (ACDC). The aim of this article is to first present the composition and structure of the mineralized bone matrix, to review the current understanding of the molecular mechanisms of mineralization, and finally to discuss the conditions associated with ectopic calcification and the underlying mechanisms.

Whole genome sequencing in adults with clinical hallmarks of hypophosphatasia negative for ALPL variants.

BACKGROUND: Hypophosphatasia (HPP) is a rare disease caused by deficient activity of tissue-nonspecific alkaline phosphatase (ALP), encoded by the ALPL gene. The primary objective was to explore novel ALPL variants by whole genome sequencing (WGS) in patients with HPP who previously tested negative by standard methods for ALPL variants. The secondary objective was to search for genes beyond ALPL that may reduce ALP activity or contribute to HPP symptoms. METHODS AND RESULTS: WGS was performed in 16 patients clinically diagnosed with HPP who had ALP activity below the normal range and tested negative for ALPL variants. Genetic variants in ALPL and genes possibly associated with low ALP activity or phenotypic overlap with HPP were assessed. All 16 patients had ALP activity below the normal range. WGS did not identify any novel disease-causing ALPL variants. Positive findings for other gene variants were identified in 4 patients: 1 patient presented with variants in COL1A1, NLRP12, and SCN9A, coding for collagen, type, I alpha-1 chain, nod-like receptor pyrin domain containing 12, and sodium voltage-gated channel alpha subunit 9, respectively; 1 presented with a heterozygous, likely pathogenic variant in P3H1 coding for prolyl 3 hydroxylase 1; 1 presented with a heterozygous pathogenic variant in SGCE, coding for sarcoglycan epsilon; and 1 presented with a heterozygous variant of uncertain significance in VDR, encoding vitamin D receptor. CONCLUSION: Genomic analysis did not identify novel ALPL variants or a pattern of disease-causing variants in genes other than ALPL to explain the HPP phenotype in these patients. REGISTRATION: Clinicaltrials.gov identifier: NCT04925804.

Efficacy and safety of asfotase alfa in patients with hypophosphatasia: A systematic review.

BACKGROUND: Hypophosphatasia (HPP) is a rare genetic disorder characterized by defective bone mineralization, leading to skeletal abnormalities and systemic complications. Asfotase alfa, a recombinant human tissue-nonspecific alkaline phosphatase (TNSALP) enzyme replacement therapy, has emerged as a promising treatment for HPP. However, a comprehensive evaluation of its efficacy and safety is warranted to guide clinical practice effectively. METHODS: The study followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and was registered in Prospective Register of Systematic Reviews (PROSPERO). A search strategy across databases found studies on asfotase alfa for HPP. Two researchers independently extracted and assessed data. This systematic review examined how the drug impacted clinical outcomes such as survival rates, musculoskeletal symptoms, respiratory function, growth measurements, dental health, quality of life, and laboratory results. RESULTS: This systematic review included 15 articles with a total of 455 HPP patients. Asfotase alfa was predominantly administered at a dose of 6 mg per kg per week among the reviewed studies. Notable findings included enhanced survival rates, relief from musculoskeletal pain, improvements in respiratory outcomes, growth parameters, dental health, and quality of life. Changes in laboratory variables indicated positive responses to treatment, including changes such as increase in alkaline phosphatase (ALP), decline in pyridoxal 5'-phosphate (PLP) and inorganic pyrophosphate (PPi) levels. CONCLUSION: Asfotase alfa demonstrates efficacy in improving clinical outcomes and safety in patients with HPP. Its therapeutic benefits extend across various domains. However, Larger, age-stratified comparative studies are needed to further investigate the drug's effects in HPP patients.

Safety, pharmacokinetics, and pharmacodynamics of efzimfotase alfa, a second-generation enzyme replacement therapy: phase 1, dose-escalation study in adults with hypophosphatasia.

Hypophosphatasia (HPP) is a rare, inherited metabolic disease caused by deficient activity of tissue-nonspecific alkaline phosphatase (TNSALP). Efzimfotase alfa (ALXN1850) is a second-generation TNSALP enzyme replacement therapy in development for HPP. This first-in-human open-label, dose-escalating phase 1 trial evaluated efzimfotase alfa safety, tolerability, pharmacokinetics, pharmacodynamics, and immunogenicity. Fifteen adults (5/cohort) with HPP received efzimfotase alfa in doses of 15 mg (cohort 1), 45 mg (cohort 2), or 90 mg (cohort 3) as one intravenous (i.v.) dose followed by 3 weekly subcutaneous (s.c.) doses. The primary objective was to assess safety and tolerability. Secondary objectives included pharmacokinetics, pharmacodynamics of ALP substrates known to be biomarkers of disease (inorganic pyrophosphate [PPi] and pyridoxal 5'-phosphate [PLP]) and immunogenicity. Treatment-emergent adverse events (TEAEs) occurred in 12 (80%) participants. Eight (53%) participants had injection site reactions (ISRs), observed after 10 of 41 (24%) s.c. injections. Most ISR TEAEs were mild and resolved within 1-2 d. Peak and total exposures of efzimfotase alfa increased in a greater-than-dose proportional manner over the range of 15-90 mg after i.v. and s.c. dosing. The arithmetic mean elimination half-life was approximately 6 d; absolute bioavailability was 28.6%-36.8% over the s.c. dose range of 15-90 mg. Dose-dependent reductions in plasma concentrations of PPi and PLP relative to baseline reached nadir in the first week after i.v. dosing and were sustained for 3-4 wk after the last s.c. dose. Four (27%) participants tested positive for antidrug antibodies (ADAs), 3 of whom were ADA positive before the first dose of efzimfotase alfa. ADAs had no apparent effect on efzimfotase alfa pharmacokinetics/pharmacodynamics. No participants had neutralizing antibodies. Efzimfotase alfa demonstrated acceptable safety, tolerability, and pharmacokinetic profiles and was associated with sustained reductions in biomarkers of disease in adults with HPP, supporting further evaluation in adult and pediatric patients. Registration: ClinicalTrials.gov NCT04980248 (https://clinicaltrials.gov/study/NCT04980248).

Hypophosphatasia (HPP) is a rare metabolic disease caused by low activity of tissue nonspecific alkaline phosphatase (TNSALP), which is an enzyme involved in the formation and healing of bone and function of other body systems. People with HPP experience fractures, difficulty moving and walking, muscle weakness, pain, fatigue (tiredness), and teeth problems. Babies with HPP often have life-threatening breathing problems, craniosynostosis (early closure of skull bones), seizures that respond to treatment with vitamin B6, failure to thrive (inability to gain weight), and weak and abnormally shaped bones. Enzyme replacement therapy (ERT) for HPP was developed to supplement defective TNSALP with active enzyme, thus improving bone health and the symptoms of HPP. Asfotase alfa, the first ERT approved for the treatment of HPP, is given by subcutaneous injection either 3 or 6 times per week. Efzimfotase alfa is a second-generation ERT that is being developed for the treatment of HPP. Although similar to asfotase alfa, efzimfotase alfa has incorporated several changes that have the potential to require lower doses and reduce injection volume and dosing frequency, thereby potentially improving the treatment experience for patients. This first-in-human study investigated the safety, tolerability, pharmacokinetics (how a drug is absorbed into, distributed throughout, and removed from the body), pharmacodynamics (effects of the drug within the body), and immunogenicity (ability of a drug to provoke an undesirable immune response) of 4 injections of efzimfotase alfa when given by intravenous and subcutaneous routes of administration to adults with HPP. Our results showed that efzimfotase alfa has acceptable safety and pharmacokinetics and is effective for reducing biomarkers (measurable substances that reflect underlying disease) when given once weekly by subcutaneous injection, supporting further evaluation of efzimfotase alfa in planned clinical trials in adult and pediatric patients with HPP.

Rare diseases: a challenge in paediatric dentistry.

Rare diseases are an often an overlooked public health problem. Although they are infrequent, occurring on average in 100-500 people per million, these diseases represent a significant challenge in paediatric dentistry due to their complex manifestations and the need for specialised care. Conditions such as X-linked hypophosphatemic rickets (XLH), hypophosphatasia (HPP), and osteogenesis imperfecta (OI) exemplify the intersection of systemic health issues and oral health, requiring a multidisciplinary approach for their effective management. Dentists frequently play a crucial role in identifying genetic alterations through their dental manifestations and then referring patients to the geneticist for a definitive diagnosis. X-linked hypophosphatemia is the most common genetic form of rickets, with a prevalence of 1/20,000 - 1/60,000. XLH is characterised by stunted growth with disproportionate short stature, bowing of the lower limbs associated with reduced motor skills, osteoarticular pain, hypotonia, and dental and periodontal anomalies. XLH is due to inactivating mutations in the PHEX gene which cause excessive production of fibroblast growth factor 23 (FGF23). Increased concentration of FGF23 represents the main pathogenetic mechanism of XLH, stimulating urinary phosphate loss and renal 24-hydroxylase activity, and reducing renal 1α-hydroxylase activity with insufficient production of 1,25 -dihydroxy-vitamin D (1,25(OH)2D). PHEX protein is also expressed in osteoblasts, osteocytes, and odontoblasts. Regardless of FGF23's systemic effects on phosphate homeostasis, odontoblast differentiation, and dentin formation, its overexpression directly reduces osteoblast differentiation and matrix mineralisation. In patients with XLH, the deficit of 1,25(OH)2D induced by FGF23 causes poor enamel mineralisation with presence of cracks on teeth surface. XLH patients have recurrent dental abscesses with fistulas. Radiographic investigations highlight a generalised enlargement of the pulp chambers, molars with short roots, and a taurodontic appearance. Hypophosphatasia (HPP) is another condition in which dental manifestations precede systemic symptoms; it is a rare genetic disease (1/300,000 for severe forms, 1/100,000 for moderate forms. The incidence is perhaps underestimated due to missed diagnosis of moderate forms of the disease). It mainly affects bone and dental mineralisation. It is caused by pathogenic variant mutations in the ALPL gene which is located on the short arm of chromosome 1 and encodes the non-tissue-specific alkaline phosphatase (TNSALP) enzyme. TNSALP deficiency results in vitamin B6 (pyridoxine) deficiency and pathological accumulation of alkaline phosphatase substrates which may be responsible for extra-osseous manifestations, such as neurologic ones (pyridoxine sensitive seizures) as well as involvement of muscles and joints (arthropathies, muscle fatigue/hypotonia). Early non-traumatic loss of primary teeth between the ages of 2 and 4 years (and sometimes earlier) with an intact, non-resorbed root is a sign of disease. Tooth mobility precedes exfoliation of the tooth/teeth, most often without associated gum inflammation or pain. The primary incisors are the most affected teeth, and the number and type of primary teeth lost are proportional to the severity of the disease. From a radiologic perspective, characteristic signs include localised or generalised horizontal alveolar bone loss, large pulp chambers, intrapulpal calcifications, and reduced enamel thickness. Osteogenesis imperfecta, or brittle bone disease, is a rare condition characterised by bone fragility and osteopenia. It combines skeletal signs of varying severity (mainly fractures, hyperlaxity, and ligament deformities) and extra skeletal signs (bluish sclera, deafness, vascular fragility). It may also involve dentinogenesis imperfecta. The severity of clinical manifestations is highly variable, ranging from moderate forms that can go unnoticed to major forms that are lethal in the perinatal period. The birth prevalence of osteogenesis imperfecta is approximately 1 in 10,000 people. In approximately 90% of cases, it is an autosomal dominant disease due to monoallelic mutations in the COL1A1, COL1A2 or IFITM5 genes. Ten percent of cases are recessive forms characterised by dentinogenesis imperfecta, where the dental manifestations include teeth discoloration and weakness. The timely recognition of dental manifestations of these rare genetic diseases can allow providers to make an early diagnosis even prior to the development of systemic complications, and for this reason paediatric dentists have a key role in the recognition and management of these patients. Once the diagnosis is suspected, the dentist should refer patients for a genetic evaluation so as to ensure multidisciplinary management and initiation of medical therapies with the collaboration of paediatricians, endocrinologists and other health specialists. The role of dental professionals is not limited to the diagnosis of these rare diseases, but it also encompasses delivering specific, patient-tailored treatments, encouraging preventive care with regular dental visits and educating patients with the ultimate goal to promote not only oral health but the patient's overall wellbeing.

Role of PLP-Level as a predictive marker for oral health status in adult hypophosphatasia.

AIM: The aim of this study was to investigate the role of pyridoxal-5-phosphate (PLP) level on the oral health status as a predictive marker in patients with hypophosphatasia (HPP). MATERIALS AND METHODS: Throughout a systematic retrospective assessment both bone metabolism and oral health status were analyzed. The oral health status was assessed by the decayed/missing/filled teeth index (DMFT), clinical attachment level (CAL), probing pocket depth (PPD), and the periodontal screening index (PSI). RESULTS: A total of 48 HPP patients (81.3% female) with a mean age of 42.21 years was included in this retrospective study. The study population was divided into two groups using the mean PLP level (87 µg/l) as a cut-off. Patients with a PLP level ≥ 87 µg/l (n = 14) showed a significantly poorer oral health status regarding DMFT index, CAL, PPD and PSI compared to patients with a PLP level < 87 µg/l (n = 34). No significant group differences for tooth loss were found. CONCLUSION: The results of the present study indicate that the PLP level is a suitable diagnostic predictor for the oral health status in HPP patients. HPP patients with PLP levels ≥ 70 µg/l should be included into a regular dental preventive program. CLINICAL RELEVANCE: The oral health status in HPP and its correlation with laboratory parameters (i.e. PLP) has been understudied. For clinical practice, the findings of the present study clearly demonstrated that high PLP levels correlate with a worse oral health status in HPP patients. Therefore, these patients should receive an intensive dental treatment and/or inclusion in a strict maintenance program in a specialized dental practice/university hospital with a PLP level ≥ 70 µg/l.

A probable case of hypophosphatasia in St Bride's Lower Churchyard (1770-1849, London, UK).

OBJECTIVES: The objective of this study was to analyse an individual whose remains are characterised by early deciduous tooth loss and multi-focal lesions on the post-cranial skeleton. MATERIALS: Skeletal remains of an immature individual buried between 1770 and 1849 in London. METHODS: The remains were examined by visual macroscopic inspection, supplemented by radiographic examination of the mandible and maxillae. A differential diagnosis with possible conditions, frequent in this archaeological context, was conducted. A comprehensive examination of dental lesions was performed to investigate the aetiologies of deciduous tooth loss. RESULTS: The individual exhibited a mosaic of skeletal and dental pathological changes, including premature loss of deciduous dentition, premature eruption of permanent teeth generalised bone loss in both the mandible and maxilla; osteomyelitis of the left radius; osteolytic lesion on the body of the second lumbar vertebra, and marked expansions of the rib shafts due to sub-periosteal new bone formation. CONCLUSION: A differential diagnosis considered indicates that the pathological changes of the individual were most likely associated with a comorbidity involving hypophosphatasia and tuberculosis. SIGNIFICANCE: We present in this study several oral signs that could alert paleopathologists and bioarcheologists to systematically consider the potential of a condition that is rarely encountered in archaeological contexts. LIMITATIONS: Due to poor preservation, this study was confined to the analysis of a partial maxilla and mandible, a left radius shaft and the axial skeleton (rib heads and vertebrae) of the individual. SUGGESTIONS FOR FURTHER RESEARCH: Further radiographic, histological and genetic analyses would confirm the diagnosis.

Catalyzing precision: unraveling the diagnostic conundrum of tunisian familial hypophosphatasia case through integrative clinical and molecular approaches.

Familial Hypophosphatasia presents a complex diagnostic challenge due to its wide-ranging clinical manifestations and genetic heterogeneity. This study aims to elucidate the molecular underpinnings of familial Hypophosphatasia within a Tunisian family harboring a rare c.896 T > C mutation in the ALPL gene, offering insights into genotype-phenotype correlations and potential therapeutic avenues. The study employs a comprehensive approach, integrating biochemical examination, genetic analysis, structural modeling, and functional insights to unravel the impact of this rare mutation. Genetic investigation revealed the presence of the p.Leu299Pro mutation within the ALPL gene in affected family members. This mutation is strategically positioned in proximity to both the catalytic site and the metal-binding domain, suggesting potential functional consequences. Homology modeling techniques were employed to predict the 3D structure of TNSALP, providing insights into the structural context of the mutation. Our findings suggest that the mutation may induce conformational changes in the vicinity of the catalytic site and metal-binding domain, potentially affecting substrate recognition and catalytic efficiency. Molecular dynamics simulations were instrumental in elucidating the dynamic behavior of the tissue-nonspecific alkaline phosphatase isozyme (TNSALP) in the presence of the p.Leu299Pro mutation. The simulations indicated alterations in structural flexibility near the mutation site, with potential ramifications for the enzyme's overall stability and function. These dynamic changes may influence the catalytic efficiency of TNSALP, shedding light on the molecular underpinnings of the observed clinical manifestations within the Tunisian family. The clinical presentation of affected individuals highlighted significant phenotypic heterogeneity, underscoring the complex genotype-phenotype correlations in familial Hypophosphatasia. Variability in age of onset, severity of symptoms, and radiographic features was observed, emphasizing the need for a nuanced understanding of the clinical spectrum associated with the p.Leu299Pro mutation. This study advances our understanding of familial Hypophosphatasia by delineating the molecular consequences of the p.Leu299Pro mutation in the ALPL gene. By integrating genetic, structural, and clinical analyses, we provide insights into disease pathogenesis and lay the groundwork for personalized therapeutic strategies tailored to specific genetic profiles. Our findings underscore the importance of comprehensive genetic and clinical evaluation in guiding precision medicine approaches for familial Hypophosphatasia.

Pediatric hypophosphatasia: avoid diagnosis missteps!

Hypophosphatasia (HPP) is the dento-osseous disorder caused by deactivating mutation(s) of ALPL, the gene that encodes the "tissue-nonspecific" isoenzyme of alkaline phosphatase (TNSALP). In HPP, 3 natural substrates of cell-surface TNSALP accumulate extracellularly; phosphoethanolamine (PEA), inorganic pyrophosphate (PPi), and pyridoxal 5'-phosphate (PLP). Hypophosphatasemia together with elevated plasma levels of PEA, PPi, and PLP comprise its biochemical signature. PPi can inhibit mineralization and in extracellular excess can impair bone and tooth hardening and perhaps explain weak muscle. Autosomal dominant or autosomal recessive inheritance from among more than 400 mutations of ALPL largely accounts for HPP's broad-ranging severity, greatest among all skeletal diseases. Pediatric HPP spans life-threatening perinatal and infantile forms, childhood forms, and odonto-HPP selectively featuring premature loss of deciduous teeth. ALPL gene testing and TNSALP supplementation therapy have bolstered familiarity with HPP, but there are new considerations for diagnosis. Herein, diagnosis of a boy's mild childhood HPP was delayed by missteps involving his medical and dental history, physical examination, radiographic findings, and clinical laboratory studies. We review how pediatric HPP is now identified. Prompt diagnosis while appreciating the broad-ranging severity of HPP underlies the safe and effective management of this inborn-error-of-metabolism.

New Empirical Bayes Models to Jointly Analyze Multiple RNA-Sequencing Data in a Hypophosphatasia Disease Study.

Hypophosphatasia is a rare inherited metabolic disorder caused by the deficiency of tissue-nonspecific alkaline phosphatase. More severe and early onset cases present symptoms of muscle weakness, diminished motor coordination, and epileptic seizures. These neurological manifestations are poorly characterized. Thus, it is urgent to discover novel differentially expressed genes for investigating the genetic mechanisms underlying the neurological manifestations of hypophosphatasia. RNA-sequencing data offer a high-resolution and highly accurate transcript profile. In this study, we apply an empirical Bayes model to RNA-sequencing data acquired from the spinal cord and neocortex tissues of a mouse model, individually, to more accurately estimate the genetic effects without bias. More importantly, we further develop two integration methods, weighted gene approach and weighted Z method, to incorporate two RNA-sequencing data into a model for enhancing the effects of genetic markers in the diagnostics of hypophosphatasia disease. The simulation and real data analysis have demonstrated the effectiveness of our proposed integration methods, which can maximize genetic signals identified from the spinal cord and neocortex tissues, minimize the prediction error, and largely improve the prediction accuracy in risk prediction.

Nomogram for predicting early hypophosphatemia in term infants.

BACKGROUND: Physiological processes rely on phosphate, which is an essential component of adenosine triphosphate (ATP). Hypophosphatasia can affect nearly every organ system in the body. It is crucial to monitor newborns with risk factors for hypophosphatemia and provide them with the proper supplements. We aimed to evaluate the risk factors and develop a nomogram for early hypophosphatemia in term infants. METHODS: We conducted a retrospective study involving 416 term infants measured serum phosphorus within three days of birth. The study included 82 term infants with hypophosphatemia (HP group) and 334 term infants without hypophosphatemia (NHP group). We collected data on the characteristics of mothers, newborn babies, and childbirth. Furthermore, univariate and multivariate logistic regression analyses were performed to identify independent risk factors for hypophosphatemia in term infants, and a nomogram was developed and validated based on the final independent risk factors. RESULTS: According to our analysis, the multivariate logistic regression analysis showed that male, maternal diabetes, cesarean delivery, lower serum magnesium, and lower birth weight were independent risk factors for early hypophosphatemia in term infants. In addition, the C-index of the developed nomogram was 0.732 (95% CI = 0.668-0.796). Moreover, the calibration curve indicated good consistency between the hypophosphatemia diagnosis and the predicted probability, and a decision curve analysis (DCA) confirmed the clinical utility of the nomogram. CONCLUSIONS: The analysis revealed that we successfully developed and validated a nomogram for predicting early hypophosphatemia in term infants.

Detection of hypophosphatasia in hospitalised adults in rheumatology and internal medicine departments: a multicentre study over 10 years.

INTRODUCTION: Hypophosphatasia (HPP) is a rare genetic disease caused by loss-of-function mutations in the ALPL gene encoding the tissue non-specific alkaline phosphatase (ALP). Mild HPP is usually misdiagnosed in adult age. While an elevated serum ALP value draws more attention than a low value, low serum ALP should be better recognised and may lead to HPP detection. METHODS: Patients were selected from the records of the biochemistry department of six University Hospitals in France. Patients were hospitalised in the departments of rheumatology and internal medicine between 2007 and 2017. RESULTS: 56 321 hospitalised patients had at least 2 serum ALP dosages and 664 of these patients had at least 2 low serum ALP≤35 UI/L. Among these 664 patients, 482 (72.6%) had fluctuating low values (mean age 62.9 years; 60% of women) and 182 patients (27.4%) had persistent low values below 35 IU/L (mean age 53.4 years; 67% of women). Among patients with persistent hypophosphatasaemia treated with bisphosphonates, 70.8% never had ALP measurement before treatment and 20.8% were treated despite an abnormal decrease of ALP. Genetic testing was performed in 18 patients and was positive in 11. Genetic diagnosis of HPP was at least 6.0% in persistent hypophosphatasaemia and at least 15.9% in patients with at least three symptoms suggestive of HPP. CONCLUSION: In this 10-year retrospective study, 0.32% of adult patients hospitalised in the rheumatology and internal medicine departments had persistently low serum ALP, and among them, 6% had genetically proven HPP. Reported hypophosphatasaemia represented only 3.6% of hospitalised patients.

Effectiveness of asfotase alfa for treatment of adults with hypophosphatasia: results from a global registry.

BACKGROUND: Hypophosphatasia (HPP) is a rare inherited disease caused by deficient activity of tissue-nonspecific alkaline phosphatase. Many adults with HPP have a high burden of disease, experiencing chronic pain, fatigue, limited mobility, and dental issues, contributing to decreased health-related quality of life (HRQoL). HPP may be treated with the enzyme replacement therapy asfotase alfa though real-world data in adults are limited. This analysis was conducted to assess the clinical effectiveness of asfotase alfa among adults in the Global HPP Registry. METHODS: The Global HPP Registry is an observational, prospective, multinational study. Adults ≥ 18 years of age were included in this analysis if they had serum alkaline phosphatase (ALP) activity below the age- and sex-adjusted reference ranges, and/or ALPL variant(s), and received asfotase alfa for ≥ 6 months. Mobility was assessed with the 6-Minute Walk Test (6MWT), and patient-reported outcomes tools were used to assess pain (Brief Pain Inventory-Short Form), quality of life (36-item Short Form Health Survey, version 2 [SF-36v2]), and disability (Health Assessment Questionnaire-Disability Index) at multiple time points from baseline through Month 36. Data were collected as per usual standard of care; patients may not have contributed data at all time points. RESULTS: A total of 190 patients met the inclusion criteria. For patients with ≥ 1 follow-up measurement, the mean distance achieved on 6MWT increased from 404 m (range 60-632 m) at baseline (n = 31) to 484 m at Month 12 (range 240-739 m; n = 18) and remained above baseline through Month 36 (n = 7). Improvements in mean self-reported pain severity scores ranged from - 0.72 (95% CI: - 1.23, - 0.21; n = 38) to - 1.13 (95% CI: - 1.76, - 0.51; n = 26) and were observed at all time points. Improvements in the Physical Component Summary score of SF-36v2 were achieved by Month 6 and sustained throughout follow-up. There was a trend toward improvement in the Mental Component Summary score of SF-36v2 at most time points, with considerable fluctuations from Months 12 (n = 28) through 36 (n = 21). The most frequent adverse events were injection site reactions. CONCLUSIONS: Adults with HPP who received asfotase alfa for ≥ 6 months experienced improvements in mobility, physical function, and HRQoL, which were maintained over 3 years of follow-up. REGISTRATION: NCT02306720; EUPAS13514.

Impressive clinical improvement and disappearance of neuropathic pain in an adult patient with hypophosphatasia treated with asfotase alfa.

Hypophosphatasia (HPP) is a rare disorder, resulting from loss-of-function variants of the ALPL gene encoding non-tissue specific alkaline phosphatase (TNSALP). Presentation varies largely, with increased severity usually occurring with earlier disease onset. Here we describe the clinical improvement of a 57-year-old woman with childhood onset HPP, after initiating treatment with asfotase alfa (Strensiq®). This was started because of the rapid and progressive radiological deterioration of bone structure after placement of nails in both upper legs for spontaneous atypical femur fracture (AFF) - like fractures. Initiation of treatment, not only resulted in stabilization of bone structure on X-rays, but within a few weeks there was a dramatic reduction of burning pain sensations in the lower legs, attributed in retrospect to neuropathic pain, and also almost complete disappearance of headaches. Additionally, unhealed metatarsal fractures finally healed after almost 10 years. Drug efficacy was further evaluated through -quality of life questionnaires and multiple tests conducted by the physiotherapist, and showed clear improvements. Within 3 months after starting asfotase alfa, the patient was able to carry out her daily tasks indoors without relying on a walker and even started electric bike rides for 20 km/day. In conclusion, treatment with asfotase alfa, halted rapid radiological bone deterioration after bilateral intramedullary femoral pen placement and strongly increased quality of life, marked by rapid disappearance of neuropathic pain, reduction in headaches and musculoskeletal pains, and enhanced muscle strength and mobility. The quick and almost complete disappearance of neuropathic pain and headache suggests a relation with disturbed levels of metabolites in HPP.

Pyridoxine challenge reflects pediatric hypophosphatasia severity and thereby examines tissue-nonspecific alkaline phosphatase's role in vitamin B6 metabolism.

Alkaline phosphatase (ALP) is detected in most human tissues. However, ALP activity is routinely assayed using high concentrations of artificial colorimetric substrates in phosphate-free laboratory buffers at lethal pH. Hypophosphatasia (HPP) is the inborn-error-of-metabolism caused by loss-of-function mutation(s) of the ALPL gene that encodes the ALP isoenzyme expressed in bone, liver, kidney, and elsewhere and is therefore designated "tissue-nonspecific" ALP (TNSALP). Consequently, HPP harbors clues concerning the biological function of this phosphohydrolase that is anchored onto the surface of cells. The biochemical signature of HPP features low serum ALP activity (hypophosphatasemia) together with elevated plasma levels of three natural substrates of TNSALP: i) phosphoethanolamine (PEA), a component of the linkage apparatus that binds ALPs and other proteins to the plasma membrane surface; ii) inorganic pyrophosphate (PPi), an inhibitor of bone and tooth mineralization; and iii) pyridoxal 5'-phosphate (PLP), the principal circulating vitameric form of vitamin B6 (B6). Autosomal dominant and autosomal recessive inheritance involving several hundred ALPL mutations underlies the remarkably broad-ranging expressivity of HPP featuring tooth loss often with muscle weakness and rickets or osteomalacia. Thus, HPP associates the "bone" isoform of TNSALP with biomineralization, whereas the physiological role of the "liver", "kidney", and other isoforms of TNSALP remains uncertain. Herein, to examine HPP's broad-ranging severity and the function of TNSALP, we administered an oral challenge of pyridoxine (PN) hydrochloride to 116 children with HPP. We assayed both pre- and post-challenge serum ALP activity and plasma levels of PLP, the B6 degradation product pyridoxic acid (PA), and the B6 vitamer pyridoxal (PL) that can enter cells. Responses were validated by PN challenge of 14 healthy adults and 19 children with metabolic bone diseases other than HPP. HPP severity was assessed using our HPP clinical nosology and patient height Z-scores. PN challenge of all study groups did not alter serum ALP activity in our clinical laboratory. In HPP, both the post-challenge PLP level and the PLP increment correlated (Ps < 0.0001) with the clinical nosology and height Z-scores (Rs = +0.6009 and + 0.4886, and Rs = -0.4846 and - 0.5002, respectively). In contrast, the plasma levels and increments of PA and PL from the PN challenge became less pronounced with HPP severity. We discuss how our findings suggest extraskeletal TNSALP primarily conditioned the PN challenge responses, and explain why they caution against overzealous B6 supplementation of HPP.

A case report of odonto-hypophosphatasia with a novel variant in the ALPL gene.

OBJECTIVES: Hypophosphatasia (HPP) is a rare skeletal dysplasia caused by variants in the alkaline phosphatase (ALPL) gene. More than 400 pathogenic variants of the ALPL gene have been registered in the ALPL gene variant database. Here, we describe the case of a Japanese child with odonto-hypophsphatasia (odonto-HPP) and a novel ALPL variant. CASE PRESENTATION: At the age of 2 years and 1 month, he prematurely lost one deciduous tooth, with the root intact, when he fell and hit his face lightly. Three months later, he lost another adjacent deciduous tooth without incentive. His serum alkaline phosphatase (ALP) level was 72 U/L. His urine phosphoethanolamine (PEA) level was extremely high at 938 µmol/mg·Cre. The serum pyridoxal 5'-phosphaye (PLP) level was 255.9 nmol/L. Based on the clinical symptoms and laboratory findings, the patient was clinically diagnosed with odonto-HPP. Genetic analysis of the ALPL gene revealed a heterozygous variant (NM_000478.6:c.1151C>A, p.Thr384Lys). CONCLUSIONS: We report a case of odonto-HPP with a novel variant in the ALPL gene. HPP is a rare disease, and the heterozygous mutation in the ALPL gene highlights the novelty of this case.

A Delphi panel to build consensus on assessing disease severity and disease progression in adult patients with hypophosphatasia in the United States.

BACKGROUND: Hypophosphatasia (HPP) is an inborn error of metabolism with a variable presentation. We conducted a modified Delphi panel to obtain expert consensus on knowledge gaps regarding disease severity and progression in adult patients with HPP. METHODS: Healthcare professionals (HCPs) with experience managing adult patients with HPP were recruited to participate in a 3-round Delphi panel (round 1: paper survey and 1:1 interview; rounds 2-3: email survey). Panelists rated the extent of their agreement with statements about disease severity and progression in adult patients with HPP. Consensus was defined as ≥ 80% agreement. RESULTS: Ten HCPs completed round 1; nine completed rounds 2 and 3. Consensus was reached on 46/120 statements derived from steering committee input. Disease severity markers in adult patients with HPP can be bone-related (recurrent/poorly healing fractures, pseudo-fractures, metatarsal fractures, osteomalacia) or involve dentition or physiologic/functional manifestations (use of mobility devices/home modifications, abnormal gait, pain). Disease progression markers can include recurrent/poorly healing low-trauma fractures, development of ectopic calcifications, and/or impairment of functional activity. Panelists supported the development of a tool to help assess disease severity in the clinic and track changes in severity over time. Panelists also highlighted the role of a multidisciplinary team, centers with expertise, and the need to refer patients when disease severity is not clear. CONCLUSIONS: These statements regarding disease severity, progression, and assessment methods address some knowledge gaps in adult patients with HPP and may be helpful for treating HCPs, although the small sample size affects the ability to generalize the healthcare provider experience.

The diagnosis of hypophosphatasia in children as a multidisciplinary effort: an expert opinion.

Hypophosphatasia (HPP) is a rare genetic disorder in which pathogenic variants of the ALPL gene lead to a marked decrease of tissue non-specific alkaline phosphatase (TNSALP) activity. Although HPP is a systemic disorder, its clinical manifestations are more evident on bones, teeth, muscle and central nervous system. The clinical spectrum ranges from severe forms with extreme skeletal deformities, respiratory impairment, seizures, to very mild forms with onset in late adulthood and few clinical signs. The diagnosis can be suspected by measurement of TNSALP activity, but the insufficient awareness among health professionals and the lack of official guidelines are responsible for delayed diagnosis in children with HPP. The purpose of the current document is to provide an expert opinion directed at optimizing the diagnostic pathway of pediatric HPP. From April to December 2022, a multidisciplinary working group of 6 experts including two pediatric endocrinologists, a pediatric neurologist, a pediatric odontologist, a clinical geneticist, and a molecular biologist gathered in a series of periodic meetings to discuss the main issues related to the diagnosis of HPP in children and formalize an Expert Opinion statement. The experts agreed on a diagnostic trail that begins with the recognition of specific clinical signs, leading to biochemical analyses of TNSALP activity and vitamin B6 serum concentration. Very important are the neurological and dental manifestation of the disease that should be thoroughly investigated. The evaluation of TNSALP activity must consider sex and age variability and low activity must be persistent. Repeated blood measurements are thus necessary. The molecular analysis is then mandatory to confirm the diagnosis and for genetic counseling.

Hypophosphatasia: presentation and response to asfotase alfa.

Hypophosphatasia (HPP) is a rare bone disease with limited scientific evidence on the tolerability and safety of its novel treatment, Asfotase Alfa (AA). We report 7 HPP patients' heterogenous presentations and the significant improvement in various clinical outcomes attained with AA shedding light on this highly effective and safe therapy. INTRODUCTION: Hypophosphatasia (HPP) is a rare inherited metabolic bone disorder characterized by a deficiency in the tissue non-specific alkaline phosphatase (TNSALP) due to loss of function mutation in the ALPL gene. HPP is associated with impaired skeletal mineralization due to elevations in inorganic pyrophosphate and altered phosphate : pyrophosphate ratio. Asfotase alfa (AA) "enzyme replacement" was approved for treatment of HPP in 2015. We present 7 patients with HPP, 5 with pediatric-onset, and 2 with adult-onset, who have been treated with AA and describe the efficacy and safety in these patients. METHODS: 7 patients (4 females, 3 males) aged 19-68 years with HPP were included in this study. Diagnosis of HPP was confirmed by DNA analysis. AA was administered in doses of 6mg/kg/week with a mean follow-up of 6 months (SD= 5). RESULTS: Subjective improvement in muscle strength, muscle pain, walking ability, and walking distance with a reduction in the use of gait aids was seen "with AA in HPP patients." Muscle strength and pain improved by up to 70% from baseline as quantified subjectively by patients. Walking distance improved by up to 100%. Patients also reported improved cognition, mood, and energy levels, with up to 90% improvement in mood and 75% improvement in energy levels. 4 out of 6 patients first noted clinical signs of improvement after 3 months of being on therapy. 1 out of the 7 patients sustained a toe fracture 10 months from being on AA. AA was well-tolerated with injection site reactions being the most reported adverse effect. CONCLUSION: HPP treatment with AA in individuals with both pediatric and adult-onset forms resulted in significant subjective improvement in musculoskeletal and cognitive manifestations in addition to patients' quality of life. The drug was well tolerated in 6 patients. 1 patient discontinued therapy because of minor adverse effects with myalgias.

Proposed diagnostic criteria for the diagnosis of hypophosphatasia in children and adolescents: results from the HPP International Working Group.

Hypophosphatasia (HPP) is a rare inborn error of metabolism that presents variably in both age of onset and severity. HPP is caused by pathogenic variants in the ALPL gene, resulting in low activity of tissue nonspecific alkaline phosphatase (TNSALP). Patients with HPP tend have a similar pattern of elevation of natural substrates that can be used to aid in diagnosis. No formal diagnostic guidelines currently exist for the diagnosis of this condition in children, adolescents, or adults. The International HPP Working Group is a comprised of a multidisciplinary team of experts from Europe and North America who have expertise in the diagnosis and management of patients with HPP. This group reviewed 93 papers through a Medline, Medline In-Process, and Embase search for the terms "HPP" and "hypophosphatasia" between 2005 and 2020 and that explicitly address either the diagnosis of HPP in children, clinical manifestations of HPP in children, or both. Two reviewers independently evaluated each full-text publication for eligibility and studies were included if they were narrative reviews or case series/reports that concerned diagnosis of pediatric HPP or included clinical aspects of patients diagnosed with HPP. This review focused on 15 initial clinical manifestations that were selected by a group of clinical experts.The highest agreement in included literature was for pathogenic or likely pathogenic ALPL variant, elevation of natural substrates, and early loss of primary teeth. The highest prevalence was similar, including these same three parameters and including decreased bone mineral density. Additional parameters had less agreement and were less prevalent. These were organized into three major and six minor criteria, with diagnosis of HPP being made when two major or one major and two minor criteria are present.