Non-specific Alkaline Phosphatase Research Articles

P074 Diagnostic Journeys of Patients with Hypophosphatasia

Abstract Background/Aims Hypophosphatasia (HPP) is an ultra-rare genetic disorder characterised by low activity of tissue non-specific alkaline phosphatase (TNAP). Due to heterogeneity of clinical presentation and lack of definitive biochemical testing, misdiagnosis and diagnostic delay are common. Methods We used information reported by HPP patients to the Rare and Undiagnosed Diseases Study (RUDY) online registry (www.rudystudy.org). We included patients with a self-reported diagnosis of HPP and information on at least one of our outcomes. We described their diagnostic journey, including diagnostic delays, initial symptoms, incorrect diagnoses and healthcare professionals seen. Results 16 participants with a self-reported diagnosis of HPP were included in the analysis with 14/16 female. Of those reporting the date of initial symptom onset, 9/14 participants had symptom onset before the age of 18, whereas five had symptom onset in adulthood. The median time from symptom onset to HPP final diagnosis was 26.5 years (N = 8, IQR 11.2 to 34.6). From the first GP visit related HPP to final diagnosis the median time was 9.5 years (N = 6, IQR 6.2 to 11.1), and from the first hospital visit related to HPP, the median time to final diagnosis was 3.9 years (N = 10, IQR 0.8 to 10.5). Among participants reporting initial symptoms (N = 13), 16 categories of initial symptom were reported, with a median of two initial symptom categories per participant (IQR 1 to 2). The most prevalent initial symptom was pain (10/13, 77%). Of these 10 participants, four had lower limb pain, one had upper limb pain, one had back pain, and five had pain of unspecified location. Skeletal deformity at birth, dental manifestations, joint swelling, and infantile feeding problems were each present in 2/13 participants (15%). Among participants reporting whether they had received other diagnoses prior to that of HPP (N = 13), nine participants (75%) received at least one other diagnosis, with diagnoses of 10 different conditions reported across the cohort. The most common other diagnosis was fibromyalgia (4/13, 31%), followed by hypermobility (2/13, 15%). 21 different types of healthcare professionals were seen prior to final diagnosis. General Practitioners were the most commonly consulted (9/14, 64%). This was followed by allied health professionals (8/14, 57%). Of the eight participants seeing allied health professionals, all eight saw physiotherapists, and 4 (29% of total) also saw at least one other allied health professional. Other types of healthcare professional seen by multiple responders included orthopaedic surgeons (5/14, 36%), rheumatologists (5/14, 36%), geneticists (4/14, 29%), endocrinologists (3/14, 21%), metabolic specialists (3/14, 21%) and dentists (2/14, 14%). Conclusion Patients typically present with a cluster of symptoms, often including pain, and are often seen by general practitioners and physiotherapists before diagnosis. Increasing awareness of HPP in these professions may improve early recognition of the disease. Disclosure D. Marsden: None. R. Ridley: None.

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

IntroductionHypophosphatasia (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....

Mechanical stretch leads to increased caveolin-1 content and mineralization potential in extracellular vesicles from vascular smooth muscle cells

BackgroundHypertension-induced mechanical stress on vascular smooth muscle cells (VSMCs) is a known risk factor for vascular remodeling, including vascular calcification. Caveolin-1 (Cav-1), an integral structural component of plasma membrane invaginations, is a mechanosensitive protein that is required for the formation of calcifying extracellular vesicles (EVs). However, the role of mechanics in Cav-1-induced EV formation from VSMCs has not been reported.ResultsExposure of VSMCs to 10% mechanical stretch (0.5 Hz) for 72 h resulted in Cav-1 translocation into non-caveolar regions of the plasma membrane and subsequent redistribution of Cav-1 from the VSMCs into EVs. Inhibition of Rho-A kinase (ROCK) in mechanically-stimulated VSMCs exacerbated the liberation of Cav-1 positive EVs from the cells, suggesting a potential involvement of actin stress fibers in this process. The mineralization potential of EVs was measured by incubating the EVs in a high phosphate solution and measuring light scattered by the minerals at 340 nm. EVs released from stretched VSMCs showed higher mineralization potential than the EVs released from non-stretched VSMCs. Culturing VSMCs in pro-calcific media and exposure to mechanical stretch increased tissue non-specific alkaline phosphatase (ALP), an important enzyme in vascular calcification, activity in EVs released from the cells, with cyclic stretch further elevating EV ALP activity compared to non-stretched cells.ConclusionOur data demonstrate that mechanical stretch alters Cav-1 trafficking and EV release, and the released EVs have elevated mineralization potential.

CD73/adenosine axis exerts cardioprotection against hypobaric hypoxia-induced metabolic shift and myocarditis in a sex-dependent manner

BackgroundClinical and experimental studies have shown that the myocardial inflammatory response during pathological events varies between males and females. However, the cellular and molecular mechanisms of these sex differences remain elusive. CD73/adenosine axis has been linked to anti-inflammatory responses, but its sex-specific cardioprotective role is unclear. The present study aimed to investigate whether the CD73/adenosine axis elicits sex-dependent cardioprotection during metabolic changes and myocarditis induced by hypobaric hypoxia.MethodsFor 7 days, male and female mice received daily injections of the CD73 inhibitor adenosine 5′- (α, β-methylene) diphosphate (APCP) 10 mg/kg/day while they were kept under normobaric normoxic and hypobaric hypoxic conditions. We evaluated the effects of hypobaric hypoxia on the CD73/adenosine axis, myocardial hypertrophy, and cardiac electrical activity and function. In addition, metabolic homeostasis and immunoregulation were investigated to clarify the sex-dependent cardioprotection of the CD73/adenosine axis.ResultsHypobaric hypoxia-induced cardiac dysfunction and adverse remodeling were more pronounced in male mice. Also, male mice had hyperactivity of the CD73/adenosine axis, which aggravated myocarditis and metabolic shift compared to female mice. In addition, CD73 inhibition triggered prostatic acid phosphatase ectonucleotidase enzymatic activity to sustain adenosine overproduction in male mice but not in female mice. Moreover, dual inhibition prostatic acid phosphatase and CD73 enzymatic activities in male mice moderated adenosine content, alleviating glycolytic shift and proinflammatory response.ConclusionThe CD73/adenosine axis confers a sex-dependent cardioprotection. In addition, extracellular adenosine production in the hearts of male mice is influenced by prostatic acid phosphatase and tissue nonspecific alkaline phosphatase.

Systemic effects of hypophosphatasia characterization of two novel variants in the ALPL gene.

Hypophosphatasia (HPP) is an inborn metabolic error caused by mutations in the ALPL gene encoding tissue non-specific alkaline phosphatase (TNSALP) and leading to decreased alkaline phosphatase (ALP) activity. Although the main characteristic of this disease is bone involvement, it presents a great genetic and clinical variability, which makes it a systemic disease. Patients were recruited based on biochemical assessments. Diagnosis was made by measuring serum ALP and pyridoxal 5-phosphate levels and finally by Sanger sequencing of the ALPL gene from peripheral blood mononuclear cells. Characterization of the new variants was performed by transfection of the variants into HEK293T cells, where ALP activity and cellular localization were measured by flow cytometry. The dominant negative effect was analyzed by co-transfection of each variant with the wild-type gene, measuring ALP activity and analyzing cellular localization by flow cytometry. Two previously undescribed variants were found in the ALPL gene: leucine 6 to serine missense mutation (c.17T>C, L6S) affecting the signal peptide and threonine 167 deletion (c.498_500delCAC, T167del) affecting the vicinity of the active site. These mutations lead mainly to non-pathognomonic symptoms of HPP. Structural prediction and modeling tools indicated the affected residues as critical residues with important roles in protein structure and function. In vitro results demonstrated low TNSALP activity and a dominant negative effect in both mutations. The results of the characterization of these variants suggest that the pleiotropic role of TNSALP could be involved in the systemic effects observed in these patients highlighting digestive and autoimmune disorders associated with TNSALP dysfunction. The two new mutations have been classified as pathogenic. At the clinical level, this study suggests that both mutations not only lead to pathognomonic symptoms of the disease, but may also play a role at the systemic level.

AML alters bone marrow stromal cell osteogenic commitment via Notch signaling.

Acute myeloid leukemia (AML) is a highly heterogeneous malignancy caused by various genetic alterations and characterized by the accumulation of immature myeloid blasts in the bone marrow (BM). This abnormal growth of AML cells disrupts normal hematopoiesis and alters the BM microenvironment components, establishing a niche supportive of leukemogenesis. Bone marrow stromal cells (BMSCs) play a pivotal role in giving rise to essential elements of the BM niche, including adipocytes and osteogenic cells. Animal models have shown that the BM microenvironment is significantly remodeled by AML cells, which skew BMSCs toward an ineffective osteogenic differentiation with an accumulation of osteoprogenitors. However, little is known about the mechanisms by which AML cells affect osteogenesis. We studied the effect of AML cells on the osteogenic commitment of normal BMSCs, using a 2D co-culture system. We found that AML cell lines and primary blasts, but not normal hematopoietic CD34+ cells, induced in BMSCs an ineffective osteogenic commitment, with an increase of the early-osteogenic marker tissue non-specific alkaline phosphatase (TNAP) in the absence of the late-osteogenic gene up-regulation. Moreover, the direct interaction of AML cells and BMSCs was indispensable in influencing osteogenic differentiation. Mechanistic studies identified a role for AML-mediated Notch activation in BMSCs contributing to their ineffective osteogenic commitment. Inhibition of Notch using a γ-secretase inhibitor strongly influenced Notch signaling in BMSCs and abrogated the AML-induced TNAP up-regulation. Together, our data support the hypothesis that AML infiltration produces a leukemia-supportive pre-osteoblast-rich niche in the BM, which can be partially ascribed to AML-induced activation of Notch signaling in BMSCs.

The challenge of hypophosphatasia diagnosis in adults: results from the HPP International Working Group Literature Surveillance.

Hypophosphatasia (HPP) is an inborn error of metabolism caused by reduced or absent activity of the tissue non-specific alkaline phosphatase (TNSALP) enzyme, resulting from pathogenic variants in the ALPL gene. Clinical presentation of HPP is highly variable, including lethal and severe forms in neonates and infants, a benign perinatal form, mild forms manifesting in adulthood, and odonto-HPP. Diagnosis of HPP remains a challenge in adults, as signs and symptoms may be mild and non-specific. Disease presentation varies widely; there are no universal signs or symptoms, and the disease often remains underdiagnosed or misdiagnosed, particularly by clinicians who are not familiar with this rare disorder. The absence of diagnosis or a delayed diagnosis may prevent optimal management for patients with this condition. Formal guidelines for the diagnosis of adults with HPP do not exist, complicating efforts for consistent diagnosis. To address this issue, the HPP International Working Group selected 119 papers that explicitly address the diagnosis of HPP in adults through a Medline, Medline In-Process, and Embase search for the terms "hypophosphatasia" and "HPP," and evaluated the pooled prevalence of 17 diagnostic characteristics, initially selected by a group of HPP clinical experts, in eligible studies and in patients included in these studies. Six diagnostic findings showed a pooled prevalence value over 50% and were considered for inclusion as major diagnostic criteria. Based on these results and according to discussion and consideration among members of the Working Group, we finally defined four major diagnostic criteria and five minor diagnostic criteria for HPP in adults. Authors suggested the integrated use of the identified major and minor diagnostic criteria, which either includes two major criteria, or one major criterion and two minor criteria, for the diagnosis of HPP in adults.

Osteoblast-lineage calcium/calmodulin-dependent kinase 2 delta and gamma regulates bone mass and quality.

Bone regulates its mass and quality in response to diverse mechanical, hormonal, and local signals. The bone anabolic or catabolic responses to these signals are often received by osteocytes, which then coordinate the activity of osteoblasts and osteoclasts on bone surfaces. We previously established that calcium/calmodulin-dependent kinase 2 (CaMKII) is required for osteocytes to respond to some bone anabolic cues in vitro. However, a role for CaMKII in bone physiology in vivo is largely undescribed. Here, we show that conditional codeletion of the most abundant isoforms of CaMKII (delta and gamma) in mature osteoblasts and osteocytes [Ocn-cre:Camk2d/Camk2g double-knockout (dCKO)] caused severe osteopenia in both cortical and trabecular compartments by 8 wk of age. In addition to having less bone mass, dCKO bones are of worse quality, with significant deficits in mechanical properties, and a propensity to fracture. This striking skeletal phenotype is multifactorial, including diminished osteoblast activity, increased osteoclast activity, and altered phosphate homeostasis both systemically and locally. These dCKO mice exhibited decreased circulating phosphate (hypophosphatemia) and increased expression of the phosphate-regulating hormone fibroblast growth factor 23. Additionally, dCKO mice expressed less bone-derived tissue nonspecific alkaline phosphatase protein than control mice. Consistent with altered phosphate homeostasis, we observed that dCKO bones were hypo-mineralized with prominent osteoid seams, analogous to the phenotypes of mice with hypophosphatemia. Altogether, these data reveal a fundamental role for osteocyte CaMKIIδ and CaMKIIγ in the maintenance of bone mass and bone quality and link osteoblast/osteocyte CaMKII to phosphate homeostasis.

The role of endomembrane homeostasis in vascular calcification

Abstract Background Cardiovascular diseases are a leading cause of mortality, with cardiovascular calcification as a prominent predictor and contributor. Microcalcifications in thin fibrous caps of atherosclerotic plaques create biomechanical instability, leading to plaque vulnerability. Recent work indicated that cellular-derived extracellular vesicles (EVs) are pivotal for microcalcification nucleation. EVs can originate from the endolysosomal system, and FYVE-Type Zinc Finger Containing Phosphoinositide Kinase (PIKfyve), a lipid kinase, plays a key role in the endolysosomal maturation. Purpose We hypothesize that alterations in endomembrane homeostasis will modulate EV cargo and, thereby, vascular calcification. Methods and Results In calcified arteries and vascular smooth muscle cells (SMCs), we observed increased PIKfyve expression. Phosphatidylinositol 3-phosphate (PI3P) - the substrate of PIKfyve - was decreased in cellular membranes of calcifying SMCs (-40%) and recovered by Apilimod, a small molecule PIKfyve inhibitor. Apilimod prevented matrix mineralization and collagen network formation in calcifying SMCs (Fig. 1A) accompanied by reduced pro-collagen 1A1 secretion (-90%). Apilimod inhibited tissue non-specific alkaline phosphatase (TNAP) – an early marker of SMC calcification on mRNA, protein and activity level. PIKfyve silencing using siRNA showed similar results. Furthermore, Apilimod caused a dose-dependent increase of EV release assessed by nanoparticle tracking analysis (Fig. 1B). Analysis of the EV cargo demonstrated that Apilimod reduces TNAP protein abundance and activity (-60%) - a characteristic cargo that may determine EV calcification potential. Apilimod-induced EVs exhibited lower mineral content and reduced aggregation potential assessed by osteosense-based flow cytometry and turbidity assays. Next, we performed transcriptome and kinome analyses to discover the underlying mechanism of PIKfye-mediated SMC calcification. These data revealed a link to adipocyte-like differentiation and SMC phenotype specifying pathways. Validation supported increased expression of adipogenic transcription factors (CEBPA, PPARG),genes of the cholesterol and fatty acid metabolism pathways (FABP3, CD36) and enhanced fatty acid (C12) uptake (Fig. 1A) by Apilimod; while SMC-specific markers (ACTA2, SM22) and key SMC transcription factors (GATA6, MYOCD) were downregulated. Finally, in Ldlr-deficient mice fed a high-fat, high-cholesterol diet for 15 weeks, Apilimod application for 5 weeks increased PI3P levels (1.6-fold) and decreased vascular calcification (Fig. 1C), but did not alter plaque size or collagen content in atherosclerotic plaques. Conclusion Disrupting endolysosomal maturation with Apilimod promotes the release of EVs with reduced calcification potential and induces a phenotypic adaption towards adipocyte-like SMCs, causing reduced SMC calcification. Anti-arteriosclerotic effects of Apilimod in vivo remain to be further investigated.Figure

Diagnostic and New Therapeutic Approaches to Two Challenging Pediatric Metabolic Bone Disorders: Hypophosphatasia and X-linked Hypophosphatemic Rickets.

The diagnosis and management of metabolic bone disease among children can be challenging. This difficulty could be due to many factors, including limited awareness of these rare conditions, the complex pathophysiology of calcium and phosphate homeostasis, the overlapping phenotype with more common disorders (such as rickets), and the lack of specific treatments for these rare disorders. As a result, affected individuals could experience delayed diagnosis or misdiagnosis, leading to improper management. In this review, we describe the challenges facing diagnostic and therapeutic approaches to two metabolic bone disorders (MBD) among children: hypophosphatasia (HPP) and X-linked hypophosphatemia (XLH). We focus on explaining the pathophysiological processes that conceptually underpin novel therapeutic approaches, as well as these conditions' clinical or radiological similarity to nutritional rickets. Particularly in areas with limited sun exposure and among patients not supplementing vitamin D, nutritional rickets are still more common than HPP and XLH, and pediatricians and primary physicians frequently encounter this disorder in their practices. More recently, our understanding of these disorders has significantly improved, leading to the development of novel therapies. Asfotas alfa, a recombinant, human-tissue, nonspecific alkaline phosphatase, improved the survival of patients with HPP. Burosumab, a human monoclonal anti-FGF23 antibody, was recently approved as a specific therapy for XLH. We also highlight the current evidence on these two specific therapies' safety and effectiveness, though long-term data are still needed. Both HPP and XLH are multisystemic disorders that should be managed by multidisciplinary teams. Finally, recognizing these conditions in early stages will enable affected children and young adults to benefit from newly introduced, specific therapies.

Compromised Muscle Properties in a Severe Hypophosphatasia Murine Model.

Hypophosphatasia (HPP) is a rare metabolic bone disorder characterized by low levels of tissue non-specific alkaline phosphatase (TNAP) that causes under-mineralization of the bone, leading to bone deformity and fractures. In addition, patients often present with chronic muscle pain, reduced muscle strength, and an altered gait. In this work, we explored dynamic muscle function in a homozygous TNAP knockout mouse model of severe juvenile onset HPP. We found a reduction in skeletal muscle size and impairment in a range of isolated muscle contractile properties. Using histological methods, we found that the structure of HPP muscles was similar to healthy muscles in fiber size, actin and myosin structures, as well as the α-tubulin and mitochondria networks. However, HPP mice had significantly fewer embryonic and type I fibers than wild type mice, and fewer metabolically active NADH+ muscle fibers. We then used oxygen respirometry to evaluate mitochondrial function and found that complex I and complex II leak respiration were reduced in HPP mice, but that there was no disruption in efficiency of electron transport in complex I or complex II. In summary, the severe HPP mouse model recapitulates the muscle strength impairment phenotypes observed in human patients. Further exploration of the role of alkaline phosphatase in skeletal muscle could provide insight into mechanisms of muscle weakness in HPP.

Evidence that pyrophosphate acts as an extracellular signalling molecule to exert direct functional effects in primary cultures of osteoblasts and osteoclasts.

Extracellular pyrophosphate (PPi) is well known for its fundamental role as a physiochemical mineralisation inhibitor. However, information about its direct actions on bone cells remains limited. This study shows that PPi decreased osteoclast formation and resorptive activity by ≤50%. These inhibitory actions were associated with reduced expression of genes involved in osteoclastogenesis (Tnfrsf11a, Dcstamp) and bone resorption (Ctsk, Car2, Acp5). In osteoblasts, PPi present for the entire (0-21days) or latter stages of culture (7-21/14-21days) decreased bone mineralisation by ≤95%. However, PPi present for the differentiation phase only (0-7/0-14days) increased bone formation (≤70%). Prolonged treatment with PPi resulted in earlier matrix deposition and increased soluble collagen levels (≤2.3-fold). Expression of osteoblast (RUNX2, Bglap) and early osteocyte (E11, Dmp1) genes along with mineralisation inhibitors (Spp1, Mgp) was increased by PPi (≤3-fold). PPi levels are regulated by tissue non-specific alkaline phosphatase (TNAP) and ecto-nucleotide pyrophosphatase/phosphodiesterase 1 (NPP1). PPi reduced NPP1 expression in both cell types whereas TNAP expression (≤2.5-fold) and activity (≤35%) were increased in osteoblasts. Breakdown of extracellular ATP by NPP1 represents a key source of PPi. ATP release from osteoclasts and osteoblasts was decreased ≤60% by PPi and by a selective TNAP inhibitor (CAS496014-12-2). Pertussis toxin, which prevents Gαi subunit activation, was used to investigate whether G-protein coupled receptor (GPCR) signalling mediates the effects of PPi. The actions of PPi on bone mineralisation, collagen production, ATP release, gene/protein expression and osteoclast formation were abolished or attenuated by pertussis toxin. Together these findings show that PPi, modulates differentiation, function and gene expression in osteoblasts and osteoclasts. The ability of PPi to alter ATP release and NPP1/TNAP expression and activity indicates that cells can detect PPi levels and respond accordingly. Our data also raise the possibility that some actions of PPi on bone cells could be mediated by a Gαi-linked GPCR.

The Global ALPL gene variant classification project: Dedicated to deciphering variants

BackgroundHypophosphatasia (HPP) is an inherited multisystem disorder predominantly affecting the mineralization of bones and teeth. HPP is caused by pathogenic variants in ALPL, which encodes tissue non-specific alkaline phosphatase (TNSALP). Variants of uncertain significance (VUS) cause diagnostic delay and uncertainty amongst patients and health care providers. ResultsThe ALPL gene variant database (https://alplmutationdatabase.jku.at/) is an open-access archive for interpretation of the clinical significance of variants reported in ALPL. The database contains coding and non-coding variants, including single nucleotide variants, insertions/deletions and structural variants affecting coding or non-coding sequences of ALPL. Each variant in the database is displayed with details explaining the corresponding pathogenicity, and all reported genotypes and phenotypes, including references. In 2021, the ALPL gene variant classification project was established to reclassify VUS and continuously assess and update genetic, phenotypic, and functional variant information in the database. For this purpose, the database provides a unique submission system for clinicians, geneticists, genetic counselors, and researchers to submit VUS within ALPL for classification. An international, multidisciplinary consortium of HPP experts has been established to reclassify the submitted VUS using a multi-step process adhering to the stringent ACMG/AMP variant classification guidelines. These steps include a clinical phenotype assessment, deep literature research including artificial intelligence technology, molecular genetic assessment, and in-vitro functional testing of variants in a co-transfection model to measure ALP residual activity. ConclusionThis classification project and the ALPL gene variant database will serve the global medical community, widen the genotypic and phenotypic HPP spectrum by reporting and characterizing new ALPL variants based on ACMG/AMP criteria and thus facilitate improved genetic counseling and medical decision-making for affected patients and families. The project may also serve as a gold standard framework for multidisciplinary collaboration for variant interpretation in other rare diseases.

Cranial Neural Crest Specific Deletion of Alpl (TNAP) via P0-Cre Causes Abnormal Chondrocyte Maturation and Deficient Cranial Base Growth.

Bone growth plate abnormalities and skull shape defects are seen in hypophosphatasia, a heritable disorder in humans that occurs due to the deficiency of tissue nonspecific alkaline phosphatase (TNAP, Alpl) enzyme activity. The abnormal development of the cranial base growth plates (synchondroses) and abnormal skull shapes have also been demonstrated in global Alpl-/- mice. To distinguish local vs. systemic effects of TNAP on skull development, we utilized P0-Cre to knockout Alpl only in cranial neural crest-derived tissues using Alpl flox mice. Here, we show that Alpl deficiency using P0-Cre in cranial neural crest leads to skull shape defects and the deficient growth of the intersphenoid synchondrosis (ISS). ISS chondrocyte abnormalities included increased proliferation in resting and proliferative zones with decreased apoptosis in hypertrophic zones. ColX expression was increased, which is indicative of premature differentiation in the absence of Alpl. Sox9 expression was increased in both the resting and prehypertrophic zones of mutant mice. The expression of Parathyroid hormone related protein (PTHrP) and Indian hedgehog homolog (IHH) were also increased. Finally, cranial base organ culture revealed that inorganic phosphate (Pi) and pyrophosphate (PPi) have specific effects on cell signaling and phenotype changes in the ISS. Together, these results demonstrate that the TNAP expression downstream of Alpl in growth plate chondrocytes is essential for normal development, and that the mechanism likely involves Sox9, PTHrP, IHH and PPi.

THU457 Variable Presentations Of Hypophosphatasia In Two Patients In The Outpatient Setting

Abstract Disclosure: A. Elmaaz: None. S. Batool: None. P. Dandona: None. Introduction: Hypophosphatasia is a rare disorder characterized by defective mineralization of bone and teeth which is caused by an autosomal inherited mutation in the tissue nonspecific alkaline phosphatase (ALP) encoding genes. Here we present two cases of multiple dental and bony defects secondary to low ALP enzyme activity due to hypophosphatasia. Case 1: A 27-year-old female with history of mitochondrial disease, gastroparesis, malabsorption syndrome, and autonomic dysfunction was referred to Endocrinology clinic because of persistently low serum ALP levels associated with recurrent muscle, joint, and bone pain since the age of 13. She had history of multiple tooth extractions because of dental developmental abnormalities and fractures. She also reported history of fractures of three of her fingers in both hands during her childhood and teenage years. The patient was adopted and was unaware of any biological family history. Physical examination was remarkable for short-statured female, 4'8". Notably, the middle phalanges in little fingers bilaterally were shorter than the other fingers. Workup showed vitamin D level of 21 (30-80) ng/ml, despite being on 50,000 IU twice a week for 6 months with normal PTH and ionized calcium levels. The repeated serum level of ALP was 24 (31-125) U/L with bone and liver isoenzymes levels of 42% and 58 % respectively. Vitamin B6 level was 13.2 (2.1-21.7) ng/ml. Bone mineral density was unremarkable. Case 2: A 53-year-old female with history of congenital left hip dysplasia, hypertension, and dyslipidemia was seen by Endocrinology service for evaluation of decreased ALP levels. She denied any history of falls or fractures. However, she reported chronic bone pain, especially in bilateral hip joints with history of multiple surgeries in her left hip joint. She had required teeth braces and multiple dental surgeries during her childhood due to dental maldevelopment. Her height was 4'8". Laboratory workup was remarkable for low serum ALP level of 30 U/L with bone isoenzyme of 24 %. Vitamin B6 level was 206.7 (2.1-21.7) ng/ml. She had elevated serum phosphorus levels with normal calcium, PTH, and vitamin D levels. Pyridoxal-5- Phosphate level was high. Bone mineral density revealed osteopenia. Conclusion: Hypophosphatasia is a rare disease, hence it could be easily missed due to high variability in clinical presentations and severity of symptoms. Low serum levels of ALP with history of bone pain, recurrent fractures, premature loss of deciduous teeth, or loss of adult dentition should raise the suspicion of hypophosphatasia. Resistance to vitamin D supplementation is another clue to the diagnosis. A multidisciplinary approach is required for appropriate management. Presentation: Thursday, June 15, 2023

THU458 Demineralization Zebras: A Rare Case Of Hypophosphatasia In An Adult Presenting With Osteopenia

Abstract Disclosure: B.P. Ramchandani: None. A. Khan: None. H. Aftab: None. Introduction: Hypophosphatasia (HPP) is a rare genetic bone disease with only 500-600 cases reported in the United States. It is characterized by mutations in the tissue non-specific alkaline phosphatase (TNSALP) gene, leading to impaired bone mineralization. HPP presenting in the perinatal period is fatal. During infancy, rachitic deformities develop by age 6 months. Children present with early loss of deciduous teeth and delayed milestones while in adulthood, HPP is characterized by recurrent fractures, osteoporosis, and muscle weakness. We describe a case of HPP diagnosed in a patient after low ALP was discovered on laboratory testing. Case: A 69-year-old female presented for the evaluation of osteopenia. She had a history of fracture of the right knee as well as fracture of the base of the right 5th metatarsal and lateral aspect cuboid, which healed well with conservative management. Dental history was significant for 5 implants over the last 15 years. She was on vitamin D supplements and had also taken risedronate for osteopenia for 14 years which was discontinued at her first visit with us. Family history was significant for osteoporosis in her mother. Initial lab studies were significant for an ALP of 29 U/L (ref range 39-113 U/L), phosphate of 4.9 mg/d (ref range 2.4-4.8 mg/dl), pyridoxal 5’-phosphate level (vitamin B6) of 308 nmol/L (ref range 20-125 nmol/l), a vitamin D 25-OH level of 20 ng/mL (ref range >30 ng/ml) and PTH of 49 pg/dl (ref range 15-88 pg/ml). Repeat lab testing done 6 months after stopping risedronate showed consistent similar results with an ALP of 32 U/L, phosphate level of 5.1 mg/dl, vitamin B6 level of 349 nmol/L, and vitamin D 25OH level of 26 ng/mL. Bone density scan revealed a lumbar spine BMD of 1.503 g/cm2 (T-score 2.5) and a mean total hip BMD of -0.3 consistent with osteoporosis of spine and osteopenia of hip. Genetic testing and counseling were offered to the patient, however she declined. Discussion: Our patient presented with recurrent fractures and loss of dentition requiring multiple dental implants in the background of osteopenia. Given persistently low serum ALP and elevated serum vitamin B6 levels her presentation suggested a diagnosis of HPP. Management includes supportive treatment with prompt treatment of fractures, and routine dental care. Although there is no approved medication for adults, enzyme therapy replacement with asfotase-alfa (a recombinant human ALP) is FDA-approved for pediatric-onset HPP which improves bone mineralization and muscle strength, however discontinuation of therapy leads to reappearance of bone hypomineralization. Once the diagnosis is made, genetic testing and counseling should be offered to prevent complications in future pregnancies. Presentation: Thursday, June 15, 2023

OR29-02 Energy Deficient Osteoblasts Inefficiently Mineralize Developing Bone In Sheep With Hypophosphatasia

Abstract Disclosure: J.C. Bertels: None. M. McCord: None. L.G. White: None. S. Huggins: None. D. Landrock: None. E.D. Giles: None. L.J. Suva: None. D. Gaddy: None. Hypophosphatasia (HPP) is a rare genetic disorder characterized by low enzymatic activity of tissue nonspecific alkaline phosphatase (TNSALP), resulting in decreased bone mineralization, muscle weakness, and premature loss of deciduous teeth. All HPP phenotypes have been characterized in our CRISPR/Cas9 gene-edited sheep model of HPP. Previous studies identified small, abnormal mitochondria in HPP sheep cells, leading to the hypothesis that reduced bone mineralization may result from decreased osteoblast (OB) differentiation and cellular energetics. To test this idea, iliac crest bone biopsies and sternal bone marrow stromal cells (BMSCs) were harvested from 1 yr old WT and HPP sheep (n=3 per genotype). Histomorphometric analysis of bone biopsies from HPP sheep revealed increased unmineralized osteoid matrix compared to WT, indicative of decreased OB activity, whereas osteoblast and osteoclast number were unchanged. To determine whether BMSCs from HPP sheep were altered from WT in regard to differentiation capacity toward the adipocyte (AD) or OB lineage, 21 day cultures of BMSCs in OB or AD differentiation medium were performed. HPP BMSCs had significantly increased AD differentiation and similar OB differentiation compared to WT. Next, high resolution respirometry of undifferentiated and differentiating cells toward either the OB or AD lineage using Seahorse XF analysis to measure oxidative respiration and glycolysis on days 0, 7, 14 and 21 of both OB and AD differentiation was performed. Results demonstrated that both undifferentiated and differentiating HPP cells (to OB and AD) had significantly decreased oxygen consumption rates (OCR) and extracellular acidification rates (ECAR), reflective of diminished maximal and ATP-linked oxidative respiration and glycolysis. When measured, intracellular ATP levels in differentiating BMSCs, both undergoing osteoblastogenic and adiopogenic differentiation, showed a higher accumulation of ATP. Collectively, these data provide the first evidence that decreased bone mineralization in HPP sheep results from decreased BMSC and OB energetics through both oxidative respiration and glycolysis. In addition, the data demonstrate that reduced TNSALP activity also leads to enhanced bone marrow adipogenesis. Coupled with our previous results demonstrating reduced oxidative respiration and glycolysis in sheep skeletal muscle, these findings demonstrate a fundamental requirement for TNSALP activity in the maintenance of normal cellular respiration and purinergic metabolism in cells of the musculoskeletal system. Moreover, they provide important insight into the potential for targeting increased cellular respiration to alleviate the deleterious effects of HPP. Presentation: Sunday, June 18, 2023

THU460 A Case Series Of Hypophosphatasia: Presentation And Response To Asfotase Alfa

Abstract Disclosure: F. Alsarraf: None. D.S. Ali: None. K. Almonaei: None. H. Al-Alwani: None. M. Brandi: Consulting Fee; Self; Aboca, Alexion Pharmaceuticals, Inc., Amolyt, Bruno Farmaceutici, Calcilytix, Kyowa Kirin, UCB. Grant Recipient; Self; Abiogen, Alexion Pharmaceuticals, Inc., Amgen Inc, Bruno Farmaceutici, Echolight, Eli Lilly & Company, Kyowa Kirin, SPA, Theramex, UCB. Speaker; Self; Abiogen, Alexion Pharmaceuticals, Inc., Amgen Inc, Bruno Farmaceutici, Calcilytix, Echolight, Eli Lilly & Company, Kyowa Kirin, SPA, Theramex, UCB. A.A. Khan: Advisory Board Member; Self; Amgen Inc, Amolyt, Takeda. Consulting Fee; Self; Amgen Inc. Grant Recipient; Self; Alexion Pharmaceuticals, Inc., Amgen Inc, Ascendis, Chugai, Radius Health, Inc, Takeda, Ultragenyx. Research Investigator; Self; Amgen Inc, Radius Health, Inc. Speaker; Self; Alexion Pharmaceuticals, Inc., Amgen Inc. 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) was approved for treatment of HPP in 2015. We present a case series of 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. Case presentation: 7 patients (4 females, 3 males) aged 19-68 years with HPP were included in this case series. 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). Management outcome: Improvement in muscle strength, muscle pain, walking ability and walking distance with a reduction in the use of gait aids was seen. 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 commonly reported adverse effect. Discussion: HPP treatment with AA in individuals with both pediatric and adult-onset forms resulted in significant improvement in musculoskeletal and cognitive manifestations in addition to patients’ quality of life. It was well tolerated in 6 patients. 1 patient discontinued therapy because of minor adverse effects with myalgias. Presentation: Thursday, June 15, 2023

THU459 Hypophosphatasia With Normal ALPL Gene Test; A Case Report

Abstract Disclosure: K. Alkwatli: None. L.Z. Khan: None. Introduction: Hypophosphatasia is a rare hereditary disorder caused by loss of tissue nonspecific alkaline phosphatase activity, an essential enzyme in phosphate metabolism. Severe cases present perinatally and in early childhood. Mild cases can present in adulthood and can be misdiagnosed. We present an interesting patient who was clinically diagnosed with hypophosphatasia despite negative molecular genetic testing. Case presentation: 40 years-old female with a history of fibromyalgia and multiple bone fractures presented to the clinic with a long-standing history of multiple cavities, severe fatigue, headaches, muscle cramps, and arthralgia. The patient had numerous fractures throughout her life that started at age five without significant trauma, including wrist, forearm, and metatarsal bones. Her family history was negative. Laboratory testing showed low alkaline phosphatase levels on multiple occasions, 28,29,30 U/L (reference range 34-123). Her vitamin B6 was elevated at 309 nmol/L (20-125). Her zinc, calcium, vitamin D, and liver function tests were all within normal limits. Bone density scan showed a Z score of -1.0 at the lumbar spine and a Z score of -0.3 at the left femoral neck. Molecular genetic testing of the ALPL gene was negative. Hypophosphatasia was diagnosed based on her clinical and lab assessments, and she is being treated with Asfotase alfa. Her clinical course is yet to be determined. Discussion: ALPL gene is responsible for encoding the tissue nonspecific alkaline phosphatase (TNALP), the main enzyme affected in patients with hypophosphatasia. TNALP degrades inorganic pyrophosphate (PPi) to inorganic phosphate (Pi), an essential element for bone mineralization. It also facilitates vitamin B6 to cross the cell membranes. Therefore, loss of function mutations of the ALPL gene cause accumulation of PPi, which impairs the calcium-phosphate hemostasis and causes damage to multiple organs. In addition, the accumulation of the active form of vitamin B6 extracellularly can result in neurological damage.Patients present with a broad spectrum of musculoskeletal, renal, dental, and neurological symptoms. The variability of the phenotypic magnitudes is thought to be due to heterogeneity in the ALPL gene mutations. Over 400s of ALPL gene mutations have been identified in patients with hypophosphatasia. Novel variants are increasingly being reported.Negative genetic testing of the ALPL gene can still be seen in patients with hypophosphatasia due to either a variant that is undetectable by current testing methodology or if the causative gene/s are not on the ALPL gene panel. Conclusion: Genetic testing is helpful in confirming the disease and providing genetic counseling; however, treatment should still be considered if patients have sufficient clinical and laboratory findings. Presentation: Thursday, June 15, 2023

THU410 Retrospective Review Of Adults Patients With Suspected Or Confirmed Hypophosphatasia At The Penn Bone Center

Abstract Disclosure: R. Tran: None. C. Hvisdas: None. M. Riordan: None. L. Novotny: None. S. Kallish: None. K. Patel: None. M. Al Mukaddam: None. Abstract: Hypophosphatasia (HPP) is a rare inherited genetic disorder that affects the mineralization of bones and teeth. HPP is the result of a pathogenic variant involving the tissue nonspecific alkaline phosphatase (ALPL) gene. The clinical presentations of HPP greatly vary from serious perinatal manifestations (respiratory failure, seizures, and death) to mild manifestations in adulthood. In adults, hallmark signs and symptoms include early loss of primary or secondary teeth, osteoporosis, osteomalacia, recurring metatarsal stress fractures, and abnormal laboratory values, such as low alkaline phosphatase (ALP), elevated phosphoethanolamine, and elevated vitamin B6.The treatment and follow up of adults with HPP are not clearly described. This retrospective study characterizes 43 patients referred to the Penn Bone Center for suspected HPP. Twelve of the 43 patients had a confirmed HPP diagnosis based on both clinical presentations and evidence of variant in the ALPL gene. The twelve patients consisted of both female and male adults between the ages of 24 to 74. In addition, the patients had abnormal ALP levels, ranging between less than 5 to 38 units per liter (normal range: 38 to 126 U/L). Six of these patients had previous or current use of asfotase alfa with variable treatment response. Two patients decided to stop treatment due to lack of clinical benefit or worsening of symptoms while on asfotase alfa therapy. Biochemical and bone mineral density follow-up while on therapy has not been shown to be helpful in monitoring treatment response. Asfotase alfa is a subcutaneously administered synthetic human alkaline phosphatase that was approved by the Federal Drug Administration (FDA) in 2015 for treatment of perinatal/infantile- and juvenile-onset hypophosphatasia. However, the efficacy of treatment in adults remain unclear at this time. Further research is required to better define the natural progression of mild or adult-onset hypophosphatasia and the patients who would benefit from enzyme therapy. Presentation: Thursday, June 15, 2023