Loss-of-Function Mutations in the ALPL Gene Presenting with Adult Onset Osteoporosis and Low Serum Concentrations of Total Alkaline Phosphatase

Clinical presentation, risk factors and management of pregnancy-associated osteoporosis: a systematic review and meta-analysis

A systematic review and meta-analysis of the presentation, risk factors and treatment response of pregnancy-associated osteoporosis was conducted involving 35 studies and 943 patients. Vertebral fractures, back pain and family history of osteoporosis were common features. Analysis of treatment response was inconclusive due to limited availability of data.

INTRODUCTION

Pregnancy-associated osteoporosis (PAO) is a rare disorder most often presenting with vertebral fractures during pregnancy or postpartum.

AIMS

This meta-analysis aimed to evaluate the presenting features of PAO, its risk factors and the effectiveness of various treatments at improving bone mineral density (BMD) and preventing further fractures.

METHODS

A systematic search of PubMed, EMBASE and Web of Science identified 35 studies comprising 943 cases of PAO. A meta-analysis was conducted to evaluate the effect of treatment on change in BMD at the lumbar spine, femoral neck and total hip.

RESULTS

Vertebral fractures and back pain occurred in 89.2% and 90.2% of cases, respectively. The diagnosis was predominantly made postpartum. The most common risk factor was a family history of osteoporosis (40.5%). Calcium and vitamin D supplements (31.8%) and teriparatide (30.8%) were the most commonly used treatments. The meta-analysis of BMD response was inconclusive due to limited availability of data. The BMD change at the lumbar spine was greater with teriparatide compared with calcium/vitamin D and bisphosphonates but this was based on only two studies. There was no difference in BMD response at the femoral neck. Recurrent fractures were reported in 12.9% with no difference between treatment groups.

CONCLUSION

While this review can assist clinicians with the diagnosis and management of PAO, it highlights some key knowledge gaps that may inform conduct of a Delphi process on the diagnosis and management of this disorder, pending conduct of randomised controlled trials.

Diagnosis and Treatment of Hypophosphatasia

Hypophosphatasia (HPP) is a rare inherited metabolic disorder characterized by deficient activity of tissue-nonspecific alkaline phosphatase (TNAP) caused by variants in the ALPL gene. Disease manifestations encompass skeletal hypomineralization with rickets and lung hypoplasia, vitamin B6-dependent seizures, craniosynostosis, and premature loss of deciduous teeth. The clinical presentation can comprise failure to thrive with muscular hypotonia, delayed motor development, and gait disturbances later in childhood. In adults, pseudofractures are a characteristic indicator of severely compromised enzyme activity, but non-canonical symptoms like generalized musculoskeletal pain, weakness, and fatigue, frequently accompanied by neuropsychiatric and gastrointestinal issues are increasingly recognized as key findings in patients with HPP. The diagnosis is based on clinical manifestations in combination with persistently low alkaline phosphatase (ALP) activity, elevated levels of ALP substrates, specifically inorganic pyrophosphate (PPi), pyridoxal 5'-phosphate (PLP) or urine phosphoethanolamine (PEA), and genetic confirmation of a causative ALPL variant. Considering the wide range of manifestations, treatment must be multimodal and tailored to individual needs. The multidisciplinary team for comprehensive management of HPP patients should include expertise to ensure disease state metabolic and musculoskeletal treatment, dental care, neurological and neurosurgical surveillance, pain management, physical therapy, and psychological care. Asfotase alfa as first-in-class enzyme replacement therapy (ERT) for HPP has been shown to improve survival, rickets, and functional outcomes in severely affected children, but further research is needed to refine how enzyme replacement can also address emerging manifestations of the disease. Prospectively, further elucidating the pathophysiology behind the diverse clinical manifestations of HPP is instrumental for improving diagnostic concepts, establishing novel means for substituting enzyme activity, and developing integrative, multimodal care.

Age- and Sex-Dynamic Fluctuations and Reference Intervals for Alkaline Phosphatase Among the Spanish Population

CONTEXT.—

Interpretation of alkaline phosphatase (ALP) activity is essential for the diagnosis of certain diseases. ALP changes during life and may vary between different populations.

OBJECTIVE.—

To establish reference intervals (RIs) and percentile charts for ALP activity in the Spanish population through a multicentric observational study and to compare the RIs to those defined in other countries.

DESIGN.—

A total of 662 350 ALP measurements from individuals ages 0 to 99 years from 9 Spanish tertiary care centers collected between 2020 and 2022 were analyzed. This study is the largest published on this topic in the literature to date.

RESULTS.—

Continuous percentile charts for ALP according to sex and age were established which can be used as RIs. Higher levels are reached during the first weeks of life. In puberty, a differential evolution is observed in both sexes, reaching a peak at 10 to 13 years of age in boys and remaining stable in girls at this age. Significant differences were also observed in adults, higher in men between ages 20 and 49 years and between ages 50 and 79 years in women, as reported in some countries.

CONCLUSIONS.—

ALP activity follows an age- and sex-dependent fluctuation with geographic differences. It is important to have appropriate reference values for each population in order to allow for a correct diagnostic interpretation and early diagnosis of diseases related to ALP abnormalities.

A novel ratiometric fluorescent probe based on an internal reference of lanthanide/nucleotide for alkaline phosphatase detection

Based on the specific hydrolytic ability of alkaline phosphatase (ALP), a novel biocompatible ratiometric lanthanide fluorescent probe based on an internal reference (CIP@SiO2-Ce/ATP-Tris) was constructed with Ce3+ as the central ion, adenosine triphosphate (ATP) as the ligand, Tris as the auxiliary ligand and ciprofloxacin (CIP) encapsulated into SiO2 nanoparticles as the reference signal. The fluorescent probe emits characteristic fluorescence at 363 nm belonging to Ce3+ as the working signal and at 435 nm belonging to CIP as the reference signal. Dephosphorylation disrupted the coordination of Ce/ATP-Tris with the enzymatic reaction of ALP, which resulted in fluorescence quenching of Ce3+. The reference fluorescence was kept stable because of the protective effect of encapsulation by SiO2. The biosensor analysis method was achieved by comparing the relationship between I435/I363 and ALP concentration. The detection limit is 0.0025 U L-1, and the linear range of detection is 0.1-20 U L-1. It was subsequently used to detect ALP in samples of fetal bovine serum and human serum, and promising results were obtained.

Epimedium applied in the clinical treatment of osteoporosis patients with periodontitis

Osteoporosis and periodontitis, prevalent in middle-aged and elderly populations, share common features of bone loss and chronic inflammation. This study explores the hypothesis that Epimedium, known for its bone-strengthening properties, may enhance the effectiveness of conventional osteoporosis treatment in patients with coexisting periodontitis. This retrospective study analyzed clinical data from 120 patients with osteoporosis and periodontitis, divided into 2 groups. The control group received calcium carbonate, vitamin D, and zoledronic acid (CC + VD + ZA) therapy, while the observation group received additional Epimedium flavonoid treatment. Outcomes assessed included changes in bone mineral density (BMD), bone metabolism markers (β-CTx, N-MID, CT, ALP), periodontal indices (PD, AL, SBI, PLI), and inflammatory markers in gingival crevicular fluid (GCF) before and 6 months posttreatment. Compared to the control group, the observation group showed significantly greater increases in lumbar spine and proximal femur BMD and reductions in BM markers (P < .05). Periodontal health metrics (PD, AL, SBI, PLI) and GCF inflammatory markers (TNF-α, IL-1β, IL-6, IL-8, hs-CRP, ICAM-1, HMGB1, PGE2) were markedly improved in the observation group, correlating with enhanced total effective rates (TER) for osteoporosis (95.0%) and periodontitis (91.7%) and a reduced adverse event rate (AER). Epimedium shows promise as an adjunctive therapy in patients with osteoporosis and periodontitis, contributing to improved BMD, reduced inflammation, and enhanced periodontal health, suggesting its potential for broader clinical application in managing these coexisting conditions.

Latent metabolic bone disease, skeletal dysplasia and other conditions related to low bone formation among 38 patients with subtrochanteric femoral fractures: a retrospective observational study

Subtrochanteric femoral fracture is rare and intractable due to the possible association with low bone formation. Retrospective analysis of 38 patients with subtrochanteric femoral fractures revealed that four patients suffered from disorders related to low bone formation and there were specific treatments for two of them.

PURPOSE

The main aim of this study was to detect latent metabolic bone diseases and skeletal dysplasia associated with low bone formation among patients with morphologic atypical femoral fracture (AFF). A second aim was to evaluate the frequency of recognized risk factors, such as antiresorptive agents, glucocorticoids, and age.

METHODS

Clinical information was retrospectively analyzed among 38 Japanese patients who were admitted to the Department of Orthopedic Surgery and Spinal Surgery and the Division of Emergency and Critical Care Medicine at the University of Tokyo Hospital with diagnoses of subtrochanteric fractures between February 2012 and March 2022.

RESULTS

Among 38 patients (including 30 females), 21 patients were aged 75 and over. Ten patients had past oral glucocorticoid use, and 18 had past antiresorptive agent use. Two patients were diagnosed with hypophosphatemic osteomalacia after the development of fractures. One patient was suspected to be a carrier of a loss-of-function variant of alkaline phosphatase, biomineralization associated (ALPL), and one other patient had previously been genetically diagnosed with pycnodysostosis. Among four patients with a diagnosis or suspicion of these metabolic bone diseases and skeletal dysplasia, four had past clinical fractures, two had past subtrochanteric femoral fractures, and two had subtrochanteric femoral fractures on both sides.

CONCLUSION

If clinicians encounter patients with morphologic AFF, latent diseases related to low bone formation should be carefully differentiated because appropriate treatment may prevent delayed union and recurrent fractures. Additionally, it may be desirable to exclude these bone diseases in advance before initiating long-term use of antiresorptive agents in osteoporotic patients by screening with serum alkaline phosphatase levels to reduce the risk of morphologic AFF.

Reversal of heavy arterial calcification in a rat model of chronic kidney disease using targeted ethylene diamine tetraacetic acid-loaded albumin nanoparticles

Background

Elastin degradation and severe calcification in the medial layer of the vessel wall, known as medial arterial calcification (MAC), is typical in the aging population and patients with metabolic disorders, such as diabetes and chronic kidney disease (CKD). We have previously reported that ethylene diamine tetraacetic acid (EDTA) delivery to the site of calcification can be achieved by tagging nanoparticles with an elastin antibody that recognizes explicitly damaged elastin, and such systemic therapy can remove focal calcium deposits from the calcified arteries in CKD rodent model. The current study aims to test whether heavy calcification seen throughout arterial tree and kidneys in CKD can be reversed with nanoparticle therapy.

Methods

Thirty healthy male Sprague-Dawley rats weighing approximately 300 g, were placed on an adenine diet for 21 non-consecutive days to induce kidney failure, followed by daily vitamin D3 (VitD3) injections for 4 sequential days to cause severe calcification throughout the cardiovascular system and kidneys. DiR-dye loaded and elastin antibody conjugated albumin nanoparticles were used to confirm the targeting of nanoparticles to the calcification area. The rats were divided into two groups for targeted removal of calcification starting at day 7 of the last doses of VitD3. The experimental group received biweekly IV injections of anti-elastin antibody conjugated EDTA loaded human serum albumin nanoparticles (EDTA-HSA-El-Ab NPs), while the sham controls received blank nanoparticles (Blank-HSA-El-Ab NPs) (5 injections in total). Micro-computed tomography (microCT) was used to analyze the extent of calcification. Reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry studies were performed for osteogenic markers, including bone morphogenic protein 2 (BMP2), runt-related transcription factor 2 (RUNX2), and tissue non-specific alkaline phosphatase (TNAP). For comparison, aortic ring organ cultures from healthy rats were treated with high phosphate to induce calcification in vitro, and then they were treated with EDTA. Human calcified femoral arteries were also treated ex vivo with EDTA-HSA-EL-Ab NPs to test if nanoparticles remove heavy calcification.

Results

EDTA-loaded nanoparticles that specifically target degraded elastin reversed existing heavy mineral deposits in arteries, as per elemental calcium analysis (124.161±34.410 µg Ca per mg of the dry aorta in Blank-HSA-El-Ab NPs vs. 100.520±19.131 µg in EDTA-HSA-El-Ab NPs group, P=0.04) and microCT (object volume, 129.001±37.785 vs. 29.815±24.169 mm3, P=0.0005). The reversal of aortic calcification was accompanied by a significant reduction of bone-associated mRNA expression of BMP2 and RUNX2 (P=0.01). Immunohistochemistry studies corroborated RT-PCR results, showing a reduction of BMP2 and RUNX2 stains in the vessel wall. The rat aortic ring culture study also showed similar results, where osteogenic genes (BMP2, RUNX2) and proteins (BMP2, RUNX2, TNAP) were suppressed upon reversal of calcification with EDTA (P=0.001). We also show ex vivo reversal of human femoral artery calcification by microCT (calcium intensity: untreated, 57.721±28.551 vs. day 6 of treatment, 5.441±3.615, P=0.01) by EDTA nanoparticle therapy.

Conclusions

This is the first study showing the removal of calcium from heavily calcified arteries by using intravenous targeted EDTA therapy. Such therapy also reversed vascular smooth muscle cell osteoblastic transition and apoptosis in the arterial tissue, thereby potentially creating an environment for suitable tissue repair.

The utility of Hibiscus sabdariffa L. to prepare metal oxides NPs for clinical application on osteoporosis supported by theoretical study

Green synthesis of metal oxides as a treatment for bone diseases is still exploring. Herein, MgO and Fe2O3 NPs were prepared from the extract of Hibiscus sabdariffa L. to study their effect on vit D3, Ca+2, and alkaline phosphatase enzyme ALP associated with osteoporosis. Computational chemistry was utilized to gain insight into the possible interactions. These oxides were characterized by X-ray diffraction, SEM, FTIR, and AFM. Results revealed that green synthesis of MgO and Fe2O3 NPs was successful with abundant. MgO NPs were in vitro applied on osteoporosis patients (n = 35) and showed a significant elevation of vit D3 and Ca+2 (0.0001 > p < 0.001) levels, compared to healthy volunteers (n = 25). Thus, Hibiscus sabdariffa L. is a good candidate to prepare MgO NPs, with a promising enhancing effect on vit D3 and Ca+2 in osteoporosis. In addition, interactions of Fe2O3 and MgO NPs with ALP were determined by molecular docking study.

Rare Causes of Musculoskeletal Pain: Thinking beyond Common Rheumatologic Diseases

Objectives

Rare metabolic bone diseases can present with symptoms mimicking more common rheumatological conditions including spondyloarthritis, osteoarthritis, and fibromyalgia. Increasing awareness of these rare diseases within the rheumatology community is vital to ensure that affected patients are diagnosed and appropriately treated. The literature includes several reports of tumour-induced osteomalacia initially diagnosed as rheumatic disease, but other rare diseases such as X-linked hypophosphatemia (XLH) and hypophosphatasia (HPP) also deserve attention. Here, we describe two cases of adult patients incorrectly diagnosed with ankylosing spondylitis and osteoarthritis who, upon referral to a metabolic bone disease specialist, were subsequently diagnosed with XLH and HPP, respectively, profoundly altering their management.

Methods

The cases were collected from Brigham and Women's Hospital, Boston, MA, USA, and Vanderbilt University Medical Center, Nashville, TN, USA.

Results

Details of the patients' respective medical and family histories are presented, and the clinical and biochemical investigations undertaken to reach the correct diagnoses are described.

Conclusion

Rheumatologists should be encouraged to think beyond common rheumatological diseases when faced with symptoms such as bone pain, muscle pain, and stiffness, especially when accompanied by manifestations including atraumatic fractures, poor dentition, and hearing loss. In cases where one of these rare diseases is suspected, referral to a metabolic bone disease specialist for confirmation of diagnosis is encouraged as effective treatment options have recently become available.

Musculoskeletal and neurocognitive clinical significance of adult hypophosphatasia

Hypophosphatasia (HPP), also called Rathbun disease, is a rare genetic disorder that is caused by the loss-of-function mutation in the ALPL gene encoding tissue non-specific alkaline phosphatase. Doctor Rathbun first described the case of a 3-week-old infant who presented with severe osteopenia, rickets, and multiple radiographic fractures, and died shortly after of epileptic seizure and respiratory distress. The term "hypophosphatasia" was coined as the patients' alkaline phosphatase levels were significantly low. Since then, our understanding of HPP has evolved, and now we appreciate causative genetic mutation and the broad spectrum of clinical presentation depending on the age of onset, severity, and skeletal involvement: perinatal, infantile, childhood, adult and odontohypophosphatasia. The new development of enzyme replacement with asfostase alfa has saved the lives of severe form of hypophosphatasia. However, it is still unclear and remains challenging how to manage adult HPP that often presents with mild and non-specific symptoms such as muscle pain, joint stiffness, fatigue, anxiety, or low bone mass, which are common in the general population and not necessarily attributed to HPP. In this review, we will present 3 unique cases of adult HPP and discuss the pathophysiology, clinical presentation particularly neuromuscular and neurocognitive symptoms and management of adult HPP.

Could Some Patients With Fibromyalgia Potentially Have Hypophosphatasia? A Retrospective Single-Center Study

OBJECTIVE

Hypophosphatasia (HPP) is a rare disease characterized by incomplete or defective bone mineralization due to a mutation in the alkaline phosphatase (ALP) gene causing low levels of ALP. Disease presentation is heterogeneous and can present as a chronic pain syndrome like fibromyalgia (FM). Our objective was to determine if there are any potential patients with HPP in the group of patients who were diagnosed with FM. Antiresorptive therapy use can trigger atypical femur fractures in patients with HPP.

METHODS

We performed a retrospective chart review of all patients 18 years or older at a single academic center who were diagnosed with FM and had either a low or a normal ALP level. The following characteristics were reviewed: biological sex; age; history of fractures; diagnosis of osteoporosis, osteopenia, osteoarthritis, and chondrocalcinosis; genetic testing; vitamin B6 level testing; and medications.

RESULTS

Six hundred eleven patients with FM were identified. Two hundred had at least one low ALP level, and 57 had at least three consecutively low measurements of ALP, 44% of which had a history of fractures. No patients had vitamin B6 levels checked. None of the patients had previous genetic testing for HPP or underwent testing for zinc or magnesium levels.

CONCLUSION

The percentage of patients with FM who were found to have consistently low ALP levels was 9.3%. None had vitamin B6 level or genetic testing, suggesting that the diagnosis was not suspected. It is important to diagnose HPP given the availability of enzyme replacement therapy to prevent complications from HPP such as fractures. Our data support screening for this condition as a part of the initial workup of FM.

Musculoskeletal pain and muscular weakness as the main symptoms of adult hypophosphatasia in a Spanish cohort: clinical characterization and identification of a new ALPL gene variant

INTRODUCTION

Hypophosphatasia (HPP) is a rare inherited disorder, caused by mutations in the alkaline phosphatase (ALPL) gene, which encodes for the tissue non-specific alkaline phosphatase (TNSALP) isoform of alkaline phosphatase (ALP). Adult HPP is one of the mild forms that presents with unspecific signs such as osteopenia, osteomalacia and muscle involvement. Our purpose was to identify and characterize possibly misdiagnosed adult HPP patients at a clinical and biochemical level.

MATERIAL AND METHODS

At the laboratory of Miguel Servet University Hospital we retrospectively reviewed serum ALP levels in adults over a 48-month period. The clinical records of individuals with consistently low ALP levels were reviewed to exclude secondary causes. Those with persistent hypophosphatasemia were screened for symptoms of HPP. The study participants were evaluated at biochemical and genetic levels.

RESULTS

We identified 705 ALP determinations (out of 384,000 processed) in 589 patients below the reference range (30 U/l). Only 21 patients with clinical signs and symptoms of HPP were selected for genetic testing. Finally, only 12 patients participated in the study, 83.3% of whom (10/12) harbored a pathogenic or likely pathogenic variant in a heterozygous state. The major symptoms of our cohort were the presence of musculoskeletal pain (100% of patients) and muscular weakness (83.3% patients).

CONCLUSION

Mild HPP patients presenting with diffuse symptoms such as musculoskeletal pain may be undiagnosed or misdiagnosed as osteoporosis patients by routine diagnosis. It is important to identify these individuals, to avoid inappropriate treatment with antiresorptive drugs.

Clinical and molecular description of the first Italian cohort of 33 subjects with hypophosphatasia

Introduction

Hypophosphatasia (HPP) is a rare genetic disease caused by inactivating variants of the ALPL gene. Few data are available on the clinical presentation in Italy and/or on Italian HPP surveys.

Methods

There were 30 suspected HPP patients recruited from different Italian tertiary cares. Biological samples and related clinical, biochemical, and anamnestic data were collected and the ALPL gene sequenced. Search for large genomic deletions at the ALPL locus (1p36) was done. Phylogenetic conservation and modeling were applied to infer the effect of the variants on the protein structure.

Results

There were 21 ALPL variants and one large genomic deletion found in 20 out of 30 patients. Unexpectedly, NGS-driven differential diagnosis allowed uncovering three hidden additional HPP cases, for a total of 33 HPP subjects. Eight out of 24 coding variants were novel and classified as "pathogenic", "likely pathogenic", and "variants of uncertain significance". Bioinformatic analysis confirmed that all the variants strongly destabilize the homodimer structure. There were 10 cases with low ALP and high VitB6 that resulted negative to genetic testing, whereas two positive cases have an unexpected normal ALP value. No association was evident with other biochemical/clinical parameters.

Discussion

We present the survey of HPP Italian patients with the highest ALPL mutation rate so far reported and confirm the complexity of a prompt recognition of the syndrome, mostly for HPP in adults. Low ALP and high VitB6 values are mandatory for the genetic screening, this latter remaining the gold standard not only to confirm the clinical diagnosis but also to make differential diagnosis, to identify carriers, to avoid likely dangerous therapy in unrecognized cases.

PER2 Promotes Odontoblastic/Osteogenic Differentiation of Dental Pulp Stem Cells by Modulating Mitochondrial Metabolism

Human dental pulp stem cells (hDPSCs) possess remarkable self-renewal and multilineage differentiation ability. PER2, an essential circadian molecule, regulates various physiological processes. Evidence suggests that circadian rhythm and PER2 participate in physiological functions of DPSCs. However, the influence of PER2 on DPSCs' differentiation remains largely unknown. This study aimed to explore the effect and potential mechanism of PER2 on hDPSCs' differentiation. Dental pulp tissues were extracted, and hDPSCs were cultured for in vitro and in vivo experiments. Dorsal subcutaneous transplantation was performed in 6-week-old male BALB/c mice. The hDPSCs' odontoblastic/osteogenic differentiation was assessed, and mitochondrial metabolism was evaluated. The results indicated PER2 expression increasing during hDPSCs' odontoblastic/osteogenic differentiation. Gain- and loss-of function studies confirmed that PER2 promoted alkaline phosphatase (ALP) activity, mineralized nodules deposition, mRNA expression of DSPP, DMP1, COL1A1 and protein expression of DSPP and DMP1 in hDPSCs. Furthermore, PER2 enhanced collagen deposition, osteodentine-like tissue formation and DSPP expression in vivo. Mitochondrial metabolic evaluation aimed to investigate the mechanism of PER2-mediated hDPSC odontoblastic/osteogenic differentiation, which showed that PER2 increased ATP synthesis, elevated mitochondrial membrane potential and changed expression of proteins regulating mitochondrial dynamics. This study demonstrated that PER2 promoted hDPSCs' odontoblastic/osteogenic differentiation, which involved mitochondrial metabolic change.

Clinical and Genetic Characteristics of Hypophosphatasia in Chinese Adults

Hypophosphatasia (HPP) is an inherited disease caused by ALPL mutation, resulting in decreased alkaline phosphatase (ALP) activity and damage to bone and tooth mineralization. The clinical symptoms of adult HPP are variable, making diagnosis challenging. This study aims to clarify the clinical and genetic characteristics of HPP in Chinese adults. There were 19 patients, including 1 with childhood-onset and 18 with adult-onset HPP. The median age was 62 (32-74) years and 16 female patients were involved. Common symptoms included musculoskeletal symptoms (12/19), dental problems (8/19), fractures (7/19), and fatigue (6/19). Nine patients (47.4%) were misdiagnosed with osteoporosis and six received anti-resorptive treatment. The average serum ALP level was 29.1 (14-53) U/L and 94.7% (18/19) of patients had ALP levels below 40 U/L. Genetic analysis found 14 ALPL mutations, including three novel mutations-c.511C>G (p.His171Ala), c.782C>A (p.Pro261Gln), and 1399A>G (p.Met467Val). The symptoms of two patients with compound heterozygous mutations were more severe than those with heterozygous mutations. Our study summarized the clinical characteristics of adult HPP patients in the Chinese population, expanded the spectrum of pathogenic mutations, and deepened clinicians' understanding of this neglected disease.

Diagnostic Approach to Patients with Low Serum Alkaline Phosphatase

Increased serum levels of alkaline phosphatase (ALP) are widely recognized as a biochemical marker of many disorders affecting the liver or bone. However, the approach for patients with low ALP phosphatase is not well-established. Low serum ALP is an epiphenomenon of many severe acute injuries and diseases. Persistently low serum ALP may be secondary to drug therapy (including antiresorptives) or a variety of acquired disorders, such as malnutrition, vitamin and mineral deficiencies, endocrine disorders, etc. Hypophosphatasia, due to pathogenic variants of the ALPL gene, which encodes tissue non-specific ALP, is the most common genetic cause of low serum ALP. Marked bone hypomineralization is frequent in severe pediatric-onset cases. However, adult forms of hypophosphatasia usually present with milder manifestations, such as skeletal pain, chondrocalcinosis, calcific periarthritis, dental problems, and stress fractures. The diagnostic approach to these patients is discussed. Measuring several ALP substrates, such as pyrophosphate, pyridoxal phosphate, or phosphoethanolamine, may help to establish enzyme deficiency. Gene analysis showing a pathogenic variant in ALPL may confirm the diagnosis. However, a substantial proportion of patients show normal results after sequencing ALPL exons. It is still unknown if those patients carry unidentified mutations in regulatory regions of ALPL, epigenetic changes, or abnormalities in other genes.

A low serum alkaline phosphatase may signal hypophosphatasia in osteoporosis clinic patients

Low serum alkaline phosphatase (ALP) was found in 9% of patients attending an osteoporosis clinic, 0.6% of hospital patients, and 2/22 with an atypical femoral fracture. Hypophosphatasia was diagnosed in 3% of osteoporosis clinic patients with low ALP. Low ALP is a screening tool for hypophosphatasia, a condition potentially aggravated by antiresorptive therapy.

INTRODUCTION

Hypophosphatasia (HPP) is an inherited disorder associated with impaired primary mineralisation of osteoid (osteomalacia). HPP may be misdiagnosed as osteoporosis, a reduction in the volume of normally mineralized bone. Both illnesses may result in fragility fractures, although stress and atypical fractures are more common in HPP. Antiresorptive therapy, first-line treatment for osteoporosis, is relatively contraindicated in HPP. Misdiagnosis and mistreatment can be avoided by recognising a low serum alkaline phosphatase (ALP). Our aim was to determine the prevalence of a low ALP (< 30 IU/L) in patients attending an osteoporosis clinic, in a hospital-wide setting, and in a group of patients with atypical femoral fractures (AFF).

METHODS

This was a retrospective study of patients attending an osteoporosis clinic at a tertiary hospital during 8 years (2012-2020). Patients were categorised into those with a transiently low ALP, those with low ALP on ≥ 2 occasions but not the majority of measurements, and those with a persistently low ALP. ALP levels were also assessed in hospital-wide records and a group of patients with AFF.

RESULTS

Of 1839 patients attending an osteoporosis clinic, 168 (9%) had ≥ 1 low ALP, 50 (2.7%) had low ALP for ≥ 2 months, and seven (0.4%) had persistently low ALP levels. HPP was diagnosed in five patients, four of whom had persistently low ALP levels. The prevalence of HPP was 0.3% in the osteoporosis clinic and 3% in patients with ≥ 1 low ALP. Low ALP occurred in 0.6% of all hospital patients and 2/22 with AFF.

CONCLUSION

Persistently low ALP in osteoporosis clinic attendees is easy to identify and signals the possibility of hypophosphatasia, a condition that may be mistaken for osteoporosis and incorrectly treated with antiresorptive therapy.

Anabolic actions of parathyroid hormone in a hypophosphatasia mouse model

Hypophosphatasia, the rare heritable disorder caused by TNAP enzyme mutations, presents wide-ranging severity of bone hypomineralization and skeletal abnormalities. Intermittent PTH (1-34) increased long bone volume in Alpl^-/- mice but did not alter the skull phenotype. PTH may have therapeutic value for adults with TNAP deficiency-associated osteoporosis.

INTRODUCTION

Hypophosphatasia is the rare heritable disorder caused by mutations in the tissue non-specific alkaline phosphatase (TNAP) enzyme leading to TNAP deficiency. Individuals with hypophosphatasia commonly present with bone hypomineralization and skeletal abnormalities. The purpose of this study was to determine the impact of intermittent PTH on the skeletal phenotype of TNAP-deficient Alpl^-/- mice.

METHODS

Alpl-/- and Alpl+/+ (wild-type; WT) littermate mice were administered PTH (1-34) (50 µg/kg) or vehicle control from days 4 to 12 and skeletal analyses were performed including gross measurements, micro-CT, histomorphometry, and serum biochemistry.

RESULTS

Alpl^-/- mice were smaller with shorter tibial length and skull length compared to WT mice. Tibial BV/TV was reduced in Alpl^-/- mice and daily PTH (1-34) injections significantly increased BV/TV and BMD but not TMD in both WT and Alpl^-/- tibiae. Trabecular spacing was not different between genotypes and was decreased by PTH in both genotypes. Serum P1NP was unchanged while TRAcP5b was significantly lower in Alpl^-/- vs. WT mice, with no PTH effect, and no differences in osteoclast numbers. Skull height and width were increased in Alpl^-/- vs. WT mice, and PTH increased skull width in WT but not Alpl^-/- mice. Frontal skull bones in Alpl^-/- mice had decreased BV/TV, BMD, and calvarial thickness vs. WT with no significant PTH effects. Lengths of cranial base bones (basioccipital, basisphenoid, presphenoid) and lengths of synchondroses (growth plates) between the cranial base bones, plus bone of the basioccipitus, were assessed. All parameters were reduced (except lengths of synchondroses, which were increased) in Alpl^-/- vs. WT mice with no PTH effect.

CONCLUSION

PTH increased long bone volume in the Alpl^-/- mice but did not alter the skull phenotype. These data suggest that PTH can have long bone anabolic activity in the absence of TNAP, and that PTH may have therapeutic value for individuals with hypophosphatasia-associated osteoporosis.

Diagnosis of Low Bone Mass Density: Serological versus Radiological Methods

Context

Bone remodeling comprises balanced coupling of bone formation and resorption, and low bone mineral density (BMD) demonstrates high rates of bone resorption. Osteoporosis is a chronic asymptomatic disease with fragile bones and impending risk of fractures mediated by minor trauma. Whereas bone mineralization and integrity are determined by calcium and vitamin D, specific serum markers such as bone specific alkaline phosphatase (ALP) and osteocalcin (OC) play a vital role in bone formation.

Materials and Methods

Serum calcium, vitamin D, ALP, and OC levels were measured in 2,145 Saudi students aged 18–22 years at Umm Al-Qura University. The BMD was measured by dual-energy X-ray absorptiometry (DEXA), and the findings were statistically evaluated. The following statistics were utilized in the analysis: the SPSS software was used to record, tabulate, and statistically evaluate the results.

Results

Low BMD cases accounted for 27.46% of all cases investigated, with considerably higher serum calcium, bone-specific ALP, and OC levels compared to control cases, but significantly lower serum vitamin D levels. In low BMD instances, there was no association between serum markers and DEXA findings.

Conclusion

Serum indicators by themselves may be useful for screening and predicting patients at risk of osteoporosis, as well as assessing treatment response. The combination of serum markers and DEXA measures is more effective in detecting low BMD.

Genetic Diagnostics in Routine Osteological Assessment of Adult Low Bone Mass Disorders

CONTEXT

Many different inherited and acquired conditions can result in premature bone fragility/low bone mass disorders (LBMDs).

OBJECTIVE

We aimed to elucidate the impact of genetic testing on differential diagnosis of adult LBMDs and at defining clinical criteria for predicting monogenic forms.

METHODS

Four clinical centers broadly recruited a cohort of 394 unrelated adult women before menopause and men younger than 55 years with a bone mineral density (BMD) Z-score < -2.0 and/or pathological fractures. After exclusion of secondary causes or unequivocal clinical/biochemical hallmarks of monogenic LBMDs, all participants were genotyped by targeted next-generation sequencing.

RESULTS

In total, 20.8% of the participants carried rare disease-causing variants (DCVs) in genes known to cause osteogenesis imperfecta (COL1A1, COL1A2), hypophosphatasia (ALPL), and early-onset osteoporosis (LRP5, PLS3, and WNT1). In addition, we identified rare DCVs in ENPP1, LMNA, NOTCH2, and ZNF469. Three individuals had autosomal recessive, 75 autosomal dominant, and 4 X-linked disorders. A total of 9.7% of the participants harbored variants of unknown significance. A regression analysis revealed that the likelihood of detecting a DCV correlated with a positive family history of osteoporosis, peripheral fractures (> 2), and a high normal body mass index (BMI). In contrast, mutation frequencies did not correlate with age, prevalent vertebral fractures, BMD, or biochemical parameters. In individuals without monogenic disease-causing rare variants, common variants predisposing for low BMD (eg, in LRP5) were overrepresented.

CONCLUSION

The overlapping spectra of monogenic adult LBMD can be easily disentangled by genetic testing and the proposed clinical criteria can help to maximize the diagnostic yield.

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.

Polymorphic variants of alkaline phosphatase gene correlate with clinical signs of adult hypophosphatasia?

We analyzed polymorphism of the ALPL gene in patients with low serum levels of tissue-nonspecific alkaline phosphatase (TNAP). The presence of three or more of the less frequent alleles of ALPL polymorphisms was associated with significantly lower TNAP serum level and higher frequencies of metatarsal fractures, which may help confirm a clinical suspicion of adult hypophosphatasia.

INTRODUCTION

Alkaline phosphatases (ALPs) are membrane-bound enzymes that hydrolyze monophosphate esters at a high pH (pH 8-10). Inorganic pyrophosphate, pyridoxal 5-phosphate, the activated form of vitamin B₆ (PLP), and phosphoethanolamine (PEA), are natural substrates of ALPs. Hypophosphatasia (HPP, OMIM 146300, 241500, 241510) is a heterogeneous rare metabolic bone disease caused by loss-of-function mutations in the tissue-nonspecific alkaline phosphatase gene (ALPL; MIM 171760) with a deficiency of TNAP. Clinical presentation of HPP in adults demonstrated a wide range of manifestations, many of which are nonspecific. In the present study, we screened the polymorphic genetic variants of ALPL in 56 subjects presenting low serum levels of TNAP and/or other clinical signs of adult HPP in order to evaluate a possible role of polymorphic variants in the diagnosis and management of HPP in adults.

METHODS

Genomic DNA was extracted from peripheral blood and ALPL gene was sequenced by PCR-based Sanger technique.

RESULTS

Fourteen different polymorphic variants were found in the study population. A lower serum level of TNAP and higher frequencies of metatarsal fractures were observed in patients bearing three or more of the minor frequency alleles (MFAs) of the ALPL polymorphic variants. The presence of some MFAs, mostly as a contemporary presence of three or more of them, was found to be mainly represented in patients having both a significantly lower level of TNAP and a higher level of vitamin B6.

CONCLUSION

The genetic analysis and presence of some polymorphic variants may be an instrument to confirm clinical and biochemical data, consider adult HPP, and help clinicians be cautious in the administration of anti-reabsorption drugs.

Biochemical, clinical and genetic characteristics in adults with persistent hypophosphatasaemia; Data from an endocrinological outpatient clinic in Denmark

Background

Hypophosphatasia (HPP) is an inborn disease caused by pathogenic variants in ALPL. Low levels of alkaline phosphatase (ALP) are a biochemical hallmark of the disease. Scarce knowledge about the prevalence of HPP in Scandinavia exists, and the variable clinical presentations make diagnostics challenging. The aim of this study was to investigate the prevalence of ALPL variants as well as the clinical and biochemical features among adults with endocrinological diagnoses and persistent hypophosphatasaemia.

Methods

A biochemical database containing ALP measurements of 26,121 individuals was reviewed to identify adults above 18 years of age with persistently low levels of ALP beneath range (≤ 35 ± 2.7 U/L). ALPL genetic testing, biochemical evaluations and assessment of clinical features by a systematic questionnaire among included patients, were performed.

Results

Among 24 participants, thirteen subjects (54.2%) revealed a disease-causing variant in ALPL and reported mild clinical features of HPP, of which musculoskeletal pain was the most frequently reported (n = 9). The variant c. 571G > A; p.(Glu191Lys) was identified in six subjects, and an unreported missense variant (c.1019A > C; p.(His340Pro)) as well as a deletion of exon 2 were detected by genetic screening. Biochemical analyses showed no significant differences in ALP (p = 0.059), the bone specific alkaline phosphatase (BALP) (p = 0.056) and pyridoxal-5′-phosphate (PLP) (p = 0.085) between patients with an ALPL variant and negative genetic screening. Patients with a variant in ALPL had significantly higher PLP levels than healthy controls (p = 0.002). We observed normal ALP activity in some patients classified as mild HPP, and slightly increased levels of PLP in two subjects with normal genetic screening and four healthy controls. Among 51 patients with persistent hypophosphatasaemia, fifteen subjects (29.4%) received antiresorptive treatment. Two patients with unrecognized HPP were treated with bisphosphonates and did not show complications due to the treatment.

Conclusions

Pathogenic variants in ALPL are common among patients with endocrinological diagnoses and low ALP. Regarding diagnostics, genetic testing is necessary to identify mild HPP due to fluctuating biochemical findings. Antiresorptive treatment is a frequent reason for hypophosphatasaemia and effects of these agents in adults with a variant in ALPL and osteoporosis remain unclear and require further studies.

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Mild HPP is overlooked among adults with endocrinological diagnoses.

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Biochemical hallmarks of HPP can fluctuate to normal among mild forms.

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Genetic screening of ALPL including MLPA is necessary to identify mild HPP.

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Musculoskeletal pain is the most common symptom in adult HPP.

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Effects of bisphosphonates in mild HPP need further studies.

Genotype-Phenotype Associations in 72 Adults with Suspected ALPL-Associated Hypophosphatasia

Hypophosphatasia (HPP) is a rare inborn error of metabolism due to a decreased activity of tissue nonspecific alkaline phosphatase (TNSALP). As the onset and severity of HPP are heterogenous, it can be challenging to determine the pathogenicity of detected rare ALPL variants in symptomatic patients. We aimed to characterize patients with rare ALPL variants to propose which patients can be diagnosed with adult HPP. We included 72 patients with (1) clinical symptoms of adult HPP or positive family history and (2) low TNSALP activity and/or high pyridoxal 5'-phosphate (PLP) levels, who underwent ALPL gene sequencing. The patients were analyzed and divided into three groups depending on ALPL variant pathogenicity according to the classification of the American College of Medical Genetics and Genomics (ACMG). Reported pathogenic (n = 34 patients), rare (n = 17) and common (n = 21) ALPL variants only were found. Muscular complaints were the most frequent symptoms (> 80%), followed by bone affection (> 50%). Tooth involvement was significantly more common in patients with pathogenic or rare ALPL variants. Seven rare variants could be classified as likely pathogenic (ACMG class 4) of which five have not yet been described. Inconclusive genetic findings and less specific symptoms make diagnosis difficult in cases where adult HPP is not obvious. As not every pathogenic or rare ALPL variant leads to a manifestation of HPP, only patients with bone complications and at least one additional complication concerning teeth, muscle, central nervous and mental system, repeated low TNSALP activity and high PLP levels should be diagnosed as adult HPP if rare ALPL gene variants of ACMG class 4 or higher support the diagnosis.

Clinical and biochemical characteristics of adults with hypophosphatasia attending a metabolic bone clinic

OBJECTIVES

This study sought to identify the clinical and biochemical characteristics that would help distinguish hypophosphatasia (HPP) from other metabolic bone diseases in adult patients attending a metabolic bone clinic by comparing patients who have genetically confirmed HPP with a group of patients with low bone mineral density (BMD) in the osteoporotic or osteopenic range.

METHODS

Data were collected from February 2016 to October 2018 for 41 patients (n = 20 in the HPP group, n = 21 in the low-BMD group) attending the metabolic bone clinic at Sheffield, United Kingdom (UK) or who were recruited via the Rare UK Diseases Study (RUDY) platform during the same period. A study questionnaire was administered to all patients, and assessments were conducted for laboratory values, physical functions, BMD, and spine imaging.

RESULTS

Patients with HPP were characterized as being younger, more likely to have metatarsal or femoral shaft fractures, and less likely to have vertebral fractures compared with patients in the low-BMD group. The HPP group had lower total and bone-specific alkaline phosphatase, higher pyridoxal 5'-phosphate (PLP), and lower, albeit sufficient, 25-hydroxyvitamin D. Low-BMD group had lower C-terminal telopeptide and tartrate-resistant acid phosphatase 5b (61.9% were on bisphosphonates at enrollment). Dual X-ray absorptiometry (DXA) analysis found that the HPP group had higher total hip and lumbar BMD T- and Z-scores compared with the low-BMD group. There were no differences found between the two groups with physical functional assessments. Results of receiver operating characteristic analysis indicated strong diagnostic accuracy of these biomarkers for HPP. Thresholds of total alkaline phosphatase (ALP) activity of 43 IU/L or less and PLP level of 120 nmol/L or more were determined to be potentially clinically useful for distinguishing HPP from other metabolic bone diseases.

CONCLUSION

This study supported the use of ALP and PLP measurements as predictive of HPP diagnosis along with certain demographic and clinical characteristics (younger age, metatarsal or femoral fractures without low mean BMD T- and Z-scores on a DXA scan) that can aid in recognizing adults who should be further evaluated for HPP. The critical values identified need to be applied to an independent sample to be tested for diagnostic accuracy.

Bone mineral density and fracture risk in adult patients with hypophosphatasia

In adult hypophosphatasia (HPP) patients, elevated lumbar spine dual X-ray absorptiometry (DXA) values are associated with markers of disease severity and disease-specific fracture risk while femoral bone mineral density (BMD), being largely unaffected by the disease severity, may still be useful to monitor other causes of increased fracture risk due to low BMD.

INTRODUCTION

Hypophosphatasia (HPP) is a rare inherited metabolic disorder due to deficient activity of the tissue-nonspecific alkaline phosphatase (TNAP). Clinical manifestation in adult HPP patients is manifold including an increased risk for fractures, but data regarding clinical significance of DXA measurement and associations with fracture risk and disease severity is scarce.

METHODS

Retrospective single-center analysis of DXA scans in patients with confirmed HPP (documented mutation, clinical symptoms, low alkaline phosphatase activity). Further data evaluation included disease-related fractures, laboratory results (alkaline phosphatase, pyridoxalphosphate, phosphoethanolamine), and medical history.

RESULTS

Analysis included 110 patients (84 female, mean age of 46.2 years) of whom 37.3% (n = 41) were harboring two mutations. Average T-Score level at the lumbar spine was - 0.1 (SD 1.9), and mean total hip T-Score was - 1.07 (SD 0.15). Both lower ALP activity and higher substrate levels (pyridoxalphosphate and phosphoethanolamine) were significantly correlated with increased lumbar spine T-Score levels (p < 0.001) while BMD at the hip was not affected by indicators of disease severity. Increased lumbar spine BMD was significantly associated with an increased risk for HPP-related fractures, prevalent in 22 (20%) patients (p < 0.001) with 21 of them having biallelic mutations.

CONCLUSION

BMD in adult HPP patients is not systematically reduced. Conversely, increased lumbar spine BMD appears to be associated with severely compromised mineralization and increased risk for HPP-related fractures while BMD at the hip appears unaffected by indicators of disease severity, suggesting suitability of this anatomic location for assessing and discerning disorders with increased fracture risk owing to reduced BMD like osteoporosis.

TRIAL REGISTRATION NUMBER

German register for clinical studies (DRKS00014022) DATE OF REGISTRATION: 02/10/2018 - retrospectively registered.

Circular RNA SIPA1L1 regulates osteoblastic differentiation of stem cells from apical papilla via miR-204-5p/ALPL pathway

BACKGROUND

Osteogenesis is a complex biological process which requires the coordination of multiple molecular mechanisms. This research aimed to explore the biological role and underlying regulatory mechanism of circSIPA1L1 during the osteogenic differentiation of stem cells from apical papilla (SCAPs).

METHODS

EdU retention assay, flow cytometry assay, and CCK-8 assay were used to evaluate the proliferation capacity of SCAPs. Western blot assay, alkaline phosphatase (ALP), and alizarin red staining (ARS) were conducted to investigate the biological roles of circSIPA1L1 and miR-204-5p. Fluorescence in situ hybridization was applied for circSIPA1L1 localization. Dual-luciferase reporter assay was performed to prove the interaction of circSIPA1L1 and miR-204-5p.

RESULTS

CircSIPA1L1 had no significant effect on the proliferative capacity of SCAPs. CircSIPA1L1 promotes osteogenic differentiation of SCAPs by serving as a miRNA sponge for miR-204-5p. Either knockdown of circSIPA1L1 or overexpression of miR-204-5p significantly suppresses osteogenic differentiation of SCAPs.

CONCLUSIONS

CircSIPA1L1 upregulates ALPL through targeting miR-204-5p and promotes the osteogenic differentiation of SCAPs.

Idiopathic Osteoporosis and Nephrolithiasis: Two Sides of the Same Coin?

Idiopathic osteoporosis and nephrolithiasis are formidable health problems showing a progressive increase in their incidence and prevalence in the last decades. These temporal trends were observed in both pediatric and adult populations worldwide. Epidemiological and experimental studies indicate that both disorders show several common pathogenic environmental and genetic factors. In this review, we analyzed the clinical characteristics common to the two disorders and the state-of-the-art knowledge regarding the genetic predisposition and the environmental factors recognized as triggers in adult and pediatric ages. As a result of this work, we propose to consider idiopathic nephrolithiasis and osteoporosis as two possible expressions of a unique clinical syndrome. Accordingly, the clinical approach to both disorders should be modified in order to program an efficient primary and secondary prevention strategy.