Acute hypophosphatasemia

Screening for Hypophosphatasia in Adult Patients at a Maximum Care Provider-Retrospective Analyses over Fifteen Years

Background/Objectives: Hypophosphatasemia (HPE) may be temporary (tHPE) in the context of severe diseases, such as sepsis or trauma, or it may persist (pHPE), indicating an adult form of hypophosphatasia (HPP; OMIM 171760), a rare metabolic bone disorder caused by pathogenic nucleotide variants (PNVs) in the ALPLgene. The aim of this study was to analyze the role of auxiliary general biomarkers in verifying low alkaline phosphatase (ALP) serum activity level as an alert parameter for PNVs in the ALPLgene, which are indicative of HPP. In this retrospective analysis, we examined adult patients with an ALP serum activity level below 21 U/L. The cohort comprised 88 patients with temporary HPE (tHPE group) and 20 patients with persistent HPE who underwent re-examination. Genetic analysis performed on 12 pHPE patients identified PNV in the ALPLgene in 11 cases (ALPL group). Hemoglobin [HB], aspartate aminotransferase [AST], gamma-glutamyl transferase [GGT], calcium, phosphate, thyrotropin [TSH], albumin, total protein, and C-reactive protein [CRP] levels represented basic biomarkers. A comparative analysis between groups employed a Student's t-test, and a Student's t-test with bootstrap sampling (n = 10.000) was performed. Results: The mean HB, ALP, calcium, albumin, and total protein levels were lower in the tHPE group compared with the ALPL group (p < 0.01). AST and CRP were increased in the tHPE group (p < 0.01). The model showed an accuracy of 90% and an AUC of 0.94, which means that it can discern the two groups ~94% of the time. Conclusions: Basic biomarker evaluation effectively supports the interpretation of a decreased ALP serum activity level in the context of suspected HPP. In patients with laboratory HPE and biomarkers within reference, a PNV in the ALPLgene is highly suspected.

The Benefits of Whole-Exome Sequencing in the Differential Diagnosis of Hypophosphatasia

Hypophosphatasia (HPP) is a rare inherited disorder characterized by the decreased activity of tissue-nonspecific alkaline phosphatase (TNSALP), caused by mutations in the ALPL gene. The aim of this study was to conduct differential diagnostics in HPP patients using whole-exome sequencing (WES). The medical records of HPP patients and the genetic testing of the ALPL gene were reviewed. Seven patients were recruited and underwent WES using the Illumina or MGI sequencing platforms. All of the exome samples were matched onto a GRCh38.p13 reference genome assembly by using the Genome Analysis ToolKit (GATK) and the BWA MEM read aligner. We present the clinical and molecular findings of the seven patients referred for genetic analyses due to a clinical and biochemical suspicion of HPP. In two patients out of three (with identified heterozygous variants in the ALPL gene), we also identified c.682T>A in exon 3 of the WNT10A gene and c.3470del in exon 23 of the SMC1A gene variants for the first time. In four patients, variants in the ALPL gene were not detected, but WES allowed us to identify for the first time rare variants (c.5651A>C in exon 36 of the TRIO gene, c.880T>G in exon 6 of the TRPV4 gene, c.32078-1G>T in intron 159 of the TTN gene, c.47720_47721del in exon 235 of the TTN gene, and c.1946G>A in exon 15 of the SLC5A1 gene) and to conduct differential diagnostics with HPP. Using WES, for the first time, we demonstrate the possibility of early differential diagnostics in HPP patients with other rare genetic diseases.

Neonatal Gut and Immune Responses to β-Casein Enriched Formula in Piglets

BACKGROUND

β-casein is the main casein constituent in human milk (HM) and a source of bioactive peptides for the developing gastrointestinal tract and immune system. Infant formulas contain less β-casein than HM, but whether different concentrations of β-casein affect tolerability and gut and immune maturation in newborns is unknown.

OBJECTIVES

Using near-term piglets as a model for newborn infants, we investigated whether increasing the β-casein fraction in bovine-based formula is clinically safe and may improve gut and immune maturation.

METHODS

Three groups of near-term pigs (96% gestation) were fed formula with bovine casein and whey protein (ratio 40:60): 1) standard skim milk casein (BCN-standard, 35% β-casein of total casein, n = 18); 2) β-casein enrichment to HM concentrations (BCN-medium, 65%, n = 19); and 3) high β-casein enrichment (BCN-high, 91%, n = 19). A reference group was fed 100% whey protein concentrate (WPC) as protein (WPC, n = 18). Intestinal and immune parameters were assessed before and after euthanasia on day 5.

RESULTS

Clinical variables (mortality, activity, body growth, and diarrhea) were similar among the groups, and no differences in intestinal or biochemical parameters were observed between BCN-standard and BCN-medium pigs. However, pigs receiving high amounts of β-casein (BCN-high) had lower small intestine weight and tended to have more intestinal complications (highest gut pathology score, permeability, and interleukin-8) than the other groups, particularly those receiving no casein (WPC pigs). Blood lymphocyte, thrombocyte, and reticulocyte counts were increased with higher β-casein, whereas eosinophil counts were reduced. In vitro blood immune cell responses were similar among groups.

CONCLUSIONS

β-casein enrichment of bovine-based formula to HM concentrations is clinically safe, as judged from newborn, near-term pigs, whereas no additional benefits to gut maturation were observed. However, excessive β-casein supplementation, beyond concentrations in HM, may potentially induce gut inflammation together with increased blood cell populations relative to natural β-casein concentrations or pure whey-based formula.

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

INTRODUCTION

Hypophosphatasia (HPP) is a rare genetic disease caused by loss-of-function mutations in the ALPL gene encoding the tissue non-specific alkaline phosphatase (ALP). Mild HPP is usually misdiagnosed in adult age. While an elevated serum ALP value draws more attention than a low value, low serum ALP should be better recognised and may lead to HPP detection.

METHODS

Patients were selected from the records of the biochemistry department of six University Hospitals in France. Patients were hospitalised in the departments of rheumatology and internal medicine between 2007 and 2017.

RESULTS

56 321 hospitalised patients had at least 2 serum ALP dosages and 664 of these patients had at least 2 low serum ALP≤35 UI/L. Among these 664 patients, 482 (72.6%) had fluctuating low values (mean age 62.9 years; 60% of women) and 182 patients (27.4%) had persistent low values below 35 IU/L (mean age 53.4 years; 67% of women). Among patients with persistent hypophosphatasaemia treated with bisphosphonates, 70.8% never had ALP measurement before treatment and 20.8% were treated despite an abnormal decrease of ALP. Genetic testing was performed in 18 patients and was positive in 11. Genetic diagnosis of HPP was at least 6.0% in persistent hypophosphatasaemia and at least 15.9% in patients with at least three symptoms suggestive of HPP.

CONCLUSION

In this 10-year retrospective study, 0.32% of adult patients hospitalised in the rheumatology and internal medicine departments had persistently low serum ALP, and among them, 6% had genetically proven HPP. Reported hypophosphatasaemia represented only 3.6% of hospitalised patients.

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

Introduction

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.

Methods

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.

Results

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.

Conclusions

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.

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.

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.

Aetiologies of low alkaline phosphatase in a Canadian Paediatric Tertiary Care Centre

Objectives

Increasingly, laboratories flag low serum alkaline phosphatase (sALP) that are age-and sex-specific in paediatrics. The aim of this study was to report clinical manifestations of paediatric patients with age-and sex-specific low sALP, thereby increasing awareness of its potential aetiologies.

Methods

This retrospective Canadian tertiary care paediatric hospital study assessed all sALP of ambulatory patients aged less than 18 years from 2015 to 2017. The hospital used a Beckman Coulter AU assay to measure sALP and compared values to the Canadian age-and sex-specific reference intervals from CALIPER. All children who had at least one subnormal age-and sex-specific sALP were evaluated. A review of medical charts of included patients was performed and demographic characteristics, medical history and diagnosis were collected, and categorized under groups of medical disorders.

Results

Of 11,874 included patients, 1,001 patients (9.2%) had low sALP. Of those, 48% (485/1,001) had transient low sALP activity and 9.6% (96/1,001) had persistently low sALP. Prolonged immobilization and inflammatory bowel disease represented the main aetiologies for persistently low sALP. Interestingly, 13.5% (13/96) of patients with persistently low sALP had no apparent aetiology.

Conclusions

Our results report aetiologies of low sALP in a Canadian paediatric population using age-and sex-specific Canadian reference ranges. This study highlights that healthcare providers should be aware that a low sALP may have clinical significance and should be repeated if warranted based on further clinical assessment.

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.

Urine phosphoethanolamine is a specific biomarker for hypophosphatasia in adults

OBJECTIVES

We investigated the utility of urine phosphoethanolamine (PEA) as a marker to aid in diagnosing and/or confirming hypophosphatasia (HPP) in adults and for monitoring patients on enzyme replacement therapy (ERT).

METHODS

Data was collected from seventy-eight adults who were referred to the Vanderbilt Program for Metabolic Bone Disease for evaluation of a possible or confirmatory HPP diagnosis between July 2014 through December 2019. Fifty-nine patients were diagnosed with HPP and nineteen were excluded from a diagnosis of HPP. The urine PEA results of those patients with a confirmed diagnosis of HPP and those patients with a diagnosis of HPP excluded were captured and compared to other laboratory and clinical parameters consistent with HPP, including alkaline phosphatase (ALP) activity, plasma pyridoxal 5'-phosphate (PLP), the presence of musculoskeletal abnormalities, and genetic testing for pathogenic mutations in ALPL.

RESULTS

Initial urine PEA values in patients in our HPP cohort and not on ERT were significantly higher (median = 150.0 nmol/mg creatinine, IQR = 82.0-202.0) compared patients in our HPP negative group (median 18.0 nmol/mg creatinine, IQR = 14.0-30.0, p < 0.0001) and higher than patients on ERT (median 65.0 nmol/mg creatinine, IQR = 45.3-79.8). Patients who began ERT had a decline in urine PEA levels after treatment with a mean decrease of 68.1 %. Plasma ALP levels were significantly lower in the group of patients with HPP and not on ERT group (median = 24.0 U/L, IQR = 15.0-29.50) compared to the patients without HPP (median = 45.50 U/L, IQR = 34.0-62.0;) and plasma PLP levels were significantly higher in the HPP non-ERT group (median = 284.0 nmol/L, IQR = 141.0-469.4) compared to the patients without HPP (median = 97.5 nmol/L, IQR = 43.7-206.0;). The area under the curve (AUC) of urine PEA, ALP, and PLP to distinguish between HPP and non-HPP patients is 0.968, 0.927 and 0.781, respectively, in our cohort. Urine PEA had 100 % specificity (95 % CI of 83.2 % to 100.0 %) for diagnosing HPP at a value >53.50 nmol/mg creatinine with a sensitivity of 88.4 %; 95%CI 75.5 to 94.9 %. ALP had a 100 % specificity (95 % CI of 82.4 % to 100.0 %) for diagnosing HPP at a value <30.5 U/L with a sensitivity of 77.2 %; (95%CI 64.8 to 86.2 %). PLP had a 100 % specificity (95 % CI of 81.6 % to 100.0 %) for diagnosing HPP at a value >436 nmol/L with a sensitivity of 26.9 %; (95%CI 16.8 to 40.3 %). The most common pathogenic or likely pathogenic mutations in our cohort were c.1250A>G (p.Asn417Ser), c.1133A>T (p.Asp378Val), c.881A>C (p.Asp294Ala), c.1171C>T (p.Arg391Cys), and c.571G>A, (p.Glu191Lys).

CONCLUSIONS

Urine PEA is a promising diagnostic and confirmatory marker for HPP in patients undergoing investigation for HPP. Urine PEA also has potential use as a marker to monitor ERT compliance. Future studies are necessary to evaluate the association between PEA levels and clinical outcomes.

Analysis of the variable factors affecting changes in the blood concentration of cyclosporine before and after transfusion of red blood cell concentrate

Background

The blood concentration of cyclosporine (CyA) is frequently elevated following the transfusion of red blood cell concentrate (RCC) to patients after allogeneic hematopoietic stem cell transplantation (HSCT). The aim of this retrospective study was to identify the variable factors affecting changes in the blood concentration of CyA before and after transfusion of RCC.

Methods

We enrolled 105 patients (age, 5–66 years) who received both CyA and transfusion after HSCT. The ratio of the measurement after transfusion to the measurement before transfusion was calculated for the hematocrit and blood concentration/dose ratio of CyA (termed the HCT ratio and the CyA ratio, respectively).

Results

The blood concentration/dose ratio of CyA was increased after transfusion compared with before transfusion (P < 0.001). The HCT ratio was significantly correlated with the CyA ratio (P = 0.23, P < 0.001). The HCT ratio, concomitant medication that could elevate CyA concentration after RCC transfusion, and difference in the alkaline phosphatase level between before and after transfusion (ΔALP) were explanatory variables associated with the variation in the CyA ratio. There was no correlation between the CyA concentration after transfusion and the change in the estimated glomerular filtration rate.

Conclusions

A change in the blood concentration/dose ratio of CyA was found to be associated with a change in the HCT, concomitant medication that could elevate CyA concentration after RCC transfusion, and ALP levels. If the HCT level rises significantly after RCC transfusion, clinicians and pharmacists should pay attention to changes in the blood CyA concentration.

Characterization of Genetic Variants of Uncertain Significance for the ALPL Gene in Patients With Adult Hypophosphatasia

Hypophosphatasia (HPP) a rare disease caused by mutations in the ALPL gene encoding for the tissue-nonspecific alkaline phosphatase protein (TNSALP), has been identified as a potentially under-diagnosed condition worldwide which may have higher prevalence than currently established. This is largely due to the overlapping of its symptomatology with that of other more frequent pathologies. Although HPP is usually associated with deficient bone mineralization, the high genetic variability of ALPL results in high clinical heterogeneity, which makes it difficult to establish a specific HPP symptomatology. In the present study, three variants of ALPL gene with uncertain significance and no previously described (p.Del Glu23_Lys24, p.Pro292Leu and p.His379Asn) were identified in heterozygosis in patients diagnosed with HPP. These variants were characterized at phenotypic, functional and structural levels. All genetic variants showed significantly lower in vitro ALP activity than the wild-type (WT) genotype (p-value <0.001). Structurally, p.His379Asn variant resulted in the loss of two Zn²⁺ binding sites in the protein dimer which may greatly affect ALP activity. In summary, we identified three novel ALPL gene mutations associated with adult HPP. The correct identification and characterization of new variants and the subsequent study of their phenotype will allow the establishment of genotype-phenotype relationships that facilitate the management of the disease as well as making it possible to individualize treatment for each specific patient. This would allow the therapeutic approach to HPP to be personalized according to the unique genetic characteristics and clinical manifestations of each patient.

Pain and health-related quality of life in patients with hypophosphatasemia with and without ALPL gene mutations

BACKGROUND

Low serum alkaline phosphatase levels are the hallmark of hypophosphatasia, a disorder due to pathogenic variants of the ALPL gene. However, some patients do not carry ALPL variants and the cause of low alkaline phosphatase remains unknown. We aimed to determine health-related quality of life in adults with low alkaline phosphatase and explore the differences between patients with and without ALPL mutations.

METHODS

We studied 35 adult patients with persistently low alkaline phosphatase unrelated to secondary acquired causes who had ALPL sequenced, and 35 controls of similar age. Three questionnaires about body pain (Brief Pain Inventory, BPI), physical disability (Health Assessment Questionnaire Disability Index, HAQ-DI), and health-related quality of life (36-item Short-Form Health Survey, SF-36) were delivered by telephone interviews.

RESULTS

The mean BPI intensity and interference scores were higher in the patient group (p=0.04 and 0.004, respectively). All domains of the HAQ instrument tended to score better in the control group, with significant differences in the "reach" score (p=0.037) and the overall mean score (0.23 vs 0.09; p=0.029). Patients scored worse than controls in several SF-36 dimensions (Role physical, p=0.039; Bodily pain p=0.046; Role emotional, p=0.025). Patients with and without pathogenic variants scored similarly across all tests, without between-group significant differences.

CONCLUSIONS

Patients with persistently low levels of alkaline phosphatase have significantly worse scores in body pain and other health-related quality of life dimensions, without differences between patients with and without pathogenic variants identified in ALPL gene. This is consistent with the latter ones carrying mutations in regulatory regions.

Endocrinology of bone mineralization: an update

Throughout the world, millions of people suffer from fragilizing osteopathies such as osteomalacia and osteoporosis.Osteomalacia is a rare disorder, corresponding to mineralization abnormalities in adult bone, as opposed to rickets in children. Renal phosphate loss and hypophosphatasia are the main causes of vitamin-resistant osteomalacia. Diagnosis is based on clinical history, phosphocalcic metabolism assessment and, if necessary, molecular characterization, and must be rapid in order to initiate the most appropriate treatment and consider new treatments such as burosumab if necessary.Osteoporosis is characterized by reduced bone mass and strength, which increases the risk of fragility fracture. Fracture-related burden is expected to increase over the coming decades linked to the aging of population and a treatment gap. In order to reduce this treatment gap, it is important to develop two strategies: improvement of screening and of treatment. Systematic screening using the FRAX® fracture risk assessment tool could be useful to increase anti-osteoporosis medical treatment and reduce fracture rates. The question of treatment sequencing in osteoporosis is another challenge, notably after denosumab cessation, complicated by a decrease in bone mineral density and increased risk of fracture. New treatments are also available, including romosozumab, a humanized monoclonal antibody which promotes bone formation and inhibits bone resorption by inhibiting sclerostin. Romosozumab is approved in several countries, including France, for treating severe osteoporosis in postmenopausal women at high risk of fracture and free of cardiovascular comorbidity.Endocrinologists need to be aware of these fragilizing osteopathies in order to improve both diagnosis and treatment.

Hypophosphatasia

Hypophosphatasia (HPP) is an inherited metabolic disease caused by loss-of-function mutations in the tissue non-specific alkaline phosphatase (TNAP) gene. Reduced activity of TNAP leads to the accumulation of its substrates, mainly inorganic pyrophosphate and pyridoxal-5′-phosphate, metabolic aberrations that largely explain the musculoskeletal and systemic features of the disease. More than 400 ALPL mutations, mostly missense, are reported to date, transmitted by either autosomal dominant or recessive mode. Severe disease is rare, with incidence ranging from 1:100,000 to 1:300,000 live births, while the estimated prevalence of the less severe adult form is estimated to be between 1:3100 to 1:508, in different countries in Europe. Presentation largely varies, ranging from death in utero to asymptomatic adults. In infants and children, clinical features include skeletal, respiratory and neurologic complications, while recurrent, poorly healing fractures, muscle weakness and arthropathy are common in adults. Persistently low serum alkaline phosphatase is the cardinal biochemical feature of the disease. Management requires a dedicated multidisciplinary team. In mild cases, treatment is usually symptomatic. Severe cases, with life-threating or debilitating complications, can be successfully treated with enzyme replacement therapy with asfotase alfa.

Prevalence of low alkaline phosphatase activity in laboratory assessment: Is hypophosphatasia an underdiagnosed disease?

Background

Tissue-nonspecific alkaline phosphatase (TNSALP) encoded by the ALPL gene is of particular importance for bone mineralization. Mutation in the ALPL gene can lead to persistent low ALP activity resulting in the rare disease Hypophosphatasia (HPP) that is characterized by disturbed bone and dental mineralization. While severe forms are extremely rare with an estimated prevalence of 1/100.000, recent studies suggest that moderate form caused by heterozygous mutations are much more frequent with an estimated prevalence of 1/508. The purpose of this study was to estimate the prevalence of low AP levels in the population based on laboratory measurements.

Methods

In this study, the prevalence of low AP activity and elevated pyridoxal-5-phosphate (PLP) levels was analyzed in 6.918.126 measurements from 2011 to 2016 at a single laboratory in northern Germany. Only laboratory values of subjects older than 18 years of age were included. Only the first measurement was included, all repeated values were excluded.

Results

In total, 8.46% of the measurements of a total of 6.918.126 values showed a value < 30 U/L. 0.59% of the subjects with an ALP activity below 30 U/L had an additional PLP measurement. Here, 6.09% showed elevated pyridoxal-5-phosphate (PLP) levels. This suggest that 0.52% (1:194) of subjects show laboratory signs of HPP.

Conclusion

These data support the genetic estimation that the prevalence of moderate forms of HPP may be significantly higher than expected. Based on these data, we recommend automatically measurement of PLP in the case of low ALP activity and a notification to the ordering physician that HPP should be included in the differential diagnosis and further exploration is recommended.

Vitamin D status of children with Paediatric Inflammatory Multisystem Syndrome Temporally associated with Severe acute respiratory syndrome coronavirus 2 (PIMS-TS)

Coronavirus disease 2019 (COVID-19) has caused mild illness in children, until the emergence of the novel hyperinflammatory condition paediatric inflammatory multisystem syndrome temporally associated with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (PIMS-TS). PIMS-TS is thought to be a post-SARS-CoV-2 immune dysregulation with excessive inflammatory cytokine release. We studied 25 hydroxyvitamin D (25OHD) concentrations in children with PIMS-TS, admitted to a tertiary paediatric hospital in the UK, due to its postulated role in cytokine regulation and immune response. Eighteen children (median (range) age 8·9 (0·3-14·6) years, male = 10) met the case definition. The majority were of Black, Asian and Minority Ethnic (BAME) origin (89 %, 16/18). Positive SARS-CoV-2 IgG antibodies were present in 94 % (17/18) and RNA by PCR in 6 % (1/18). Seventy-eight percentage of the cohort were vitamin D deficient (< 30 nmol/l). The mean 25OHD concentration was significantly lower when compared with the population mean from the 2015/16 National Diet and Nutrition Survey (children aged 4–10 years) (24 v. 54 nmol/l (95 % CI −38·6, −19·7); P < 0·001). The paediatric intensive care unit (PICU) group had lower mean 25OHD concentrations compared with the non-PICU group, but this was not statistically significant (19·5 v. 31·9 nmol/l; P = 0·11). The higher susceptibility of BAME children to PIMS-TS and also vitamin D deficiency merits contemplation. Whilst any link between vitamin D deficiency and the severity of COVID-19 and related conditions including PIMS-TS requires further evidence, public health measures to improve vitamin D status of the UK BAME population have been long overdue.

[Prevalence of hypophosphatasia in adult patients in rheumatology]

Hintergrund

Die Hypophosphatasie (HPP) ist eine genetische Erkrankung, die durch eine oder mehrere Mutationen im Gen für alkalische Phosphatase (ALP) verursacht wird, verantwortlich für die Kodierung der gewebespezifischen ALP und für den Mineralisierungsprozess.

Ziel der Arbeit

Bestimmung der Prävalenz der HPP bei rheumatologischen Patienten.

Material und Methoden

Retrospektive Analyse der Krankenakten aller erwachsener Patienten mit pathologisch erniedrigten gesamt ALP-Werten (<35 U/l), die zwischen Januar 2017 und Juni 2019 in der Rheumatologie der Medizinischen Klinik III am Universitätsklinikum Bonn behandelt wurden. Die Analyse wurde in Bezug auf klinische Zeichen sowie auf die Ergebnisse der Gentests für HPP untersucht.

Ergebnisse

Bei 60 von 2289 Patienten (2,62 %) zeigten sich pathologisch niedrige ALP-Werte, bei 30 von ihnen (1,31 %) wurden persistierend niedrige ALP-Werte festgestellt. Bei 19 dieser 30 Patienten wurde ein Gentest für ALP-Genmutationen durchgeführt. Sieben der 19 Patienten (36,84 %) hatten HPP-Zeichen (Insuffizienzfrakturen oder schlechter Zahnstatus seit der Kindheit), alle mit pathologischer ALP-Mutation. Drei dieser Patienten (15,78 %) hatten jeweils eine Insuffizienzfraktur mit normwertiger Knochendichtemessung in der Vorgeschichte. Insgesamt 13 von 19 Patienten wiesen (68,42 %) Mutationen im ALP-Gen auf. Interessanterweise wurde keine Assoziation mit einer Chondrokalzinose festgestellt.

Diskussion

Die HPP scheint eine unterdiagnostizierte Erkrankung mit einem höheren Anteil betroffener Patienten, welche in der Rheumatologie vorstellig werden, zu sein. Daher sollten zukünftige Studien darauf abzielen, ein Diagnostikprotokoll in der klinischen Praxis zu entwickeln.

Clinical Significance of Hypophosphatasemia in Children

Low serum alkaline phosphatase (sALP)-hypophosphatasemia-is a characteristic of hypophosphatasia (HPP), but related to several clinical conditions. Here, we evaluated the frequency, persistency and the etiology of hypophosphatasemia in children. In retrospective analyses of sALP measurements from children, evaluated according to in-house constructed age- and sex-specific reference ranges, patients with no normal sALP measurement (Unresolved hypophosphatasemia) were invited for reanalysis. Prospectively, ALP substrates, pyridoxal-5-phosphate (PLP), and phosphoethanolamine (PEA) were measured in patients with persistent hypophosphatasemia. Radiographs and ALPL gene sequencing for HPP were performed to the cases with elevated PEA and/or PLP. From 130,340 sALP measurements of 93,162 patients, hypophosphatasemia was detected in 1404 samples from 867 patients (0.9%). Among them, 745 had at least one normal sALP values in laboratory records, grouped as transient hypophosphatasemia. 75 out of 122 patients with unresolved hypophosphatasemia could be reanalyzed for sALP, of whom PLP and PEA measurements were required in 37 due to persistent hypophosphatasemia. Both PEA and PLP were elevated in 4 patients, and ALPL gene analysis showed heterozygous mutations in 3 patients and homozygous in 1 patient. Elevated PEA with normal PLP were detected in 3 patients, and one had a heterozygous ALPL mutation. Anemia was the most common diagnosis, and upper respiratory tract infections and chronic diseases were more common in transient and unresolved hypophosphatasemia, respectively. In conclusion, reflected persistent hypophosphatasemia frequency was 1/1552 (0.06%) in this large pediatric cohort and, ALPL gene mutations were detected in 13.5% (5/37) of the studied cases. Although biochemical hypophosphatasemia is not uncommon, clinically significant HPP is rare.

Epidemiological, Clinical and Genetic Study of Hypophosphatasia in A Spanish Population: Identification of Two Novel Mutations in The Alpl Gene

Hypophosphatasia (HPP) is a genetic disease caused by one or several mutations in ALPL gene encoding the tissue-nonspecific alkaline phosphatase affecting the mineralization process. Due to its low prevalence and lack of recognition, this metabolic disorder is generally confused with other more frequent bone disorders. An assessment of serum total alkaline phosphatase (ALP) levels was performed in 78,590 subjects. Pyridoxal-5′-phosphate (PLP) concentrations were determined and ALPL gene was sequenced in patients potentially affected by HPP. Functional validation of the novel mutations found was performed using a cell-based assay. Our results showed persistently low serum ALP levels in 0.12% of subjects. Among the studied subjects, 40% presented with HPP-related symptoms. Nine of them (~28%) had a history of fractures, 5 (~16%) subjects showed chondrocalcinosis and 4 (~13%) subjects presented with dental abnormalities. Eleven subjects showed increased PLP concentrations. Seven of them showed ALPL gene mutations (2 of the mutations corresponded to novel genetic variants). In summary, we identified two novel ALPL gene mutations associated with adult HPP. Using this protocol, almost half of the studied patients were diagnosed with HPP. Based on these results, the estimated prevalence of mild HPP in Spain could be up to double than previously reported.

Biological secondary contributors to osteoporosis in fractured patients, is an early systematic assay relevant?

OBJECTIVE

To evaluate the prevalence of biological abnormalities leading to secondary osteoporosis in recently fractured patients.

METHODS

Adults older than 50, hospitalized for a non-vertebral fracture from July 2015 to October 2016, were assessed for bone fragility contributors in the orthopedics department. Bone mineral density (BMD) measurements and vertebral fracture assessment (VFA) were performed within 3 months. We assessed the prevalence of biological abnormalities in all the patients with recent fracture and in subgroups.

RESULTS

Among 439 hospitalized patients for non-vertebral low trauma fracture, 372 had biological tests (285 women, mean age 77.5 ± 13 years) and 353 (94.6%) had at least ≥ 1 biological abnormality, most frequently vitamin D insufficiency (< 75 nmol/L) (80%). Hypercalcemia was found in 22 (7.7%) patients, explained by possible primary hyperparathyroidism in 6 cases, and by the other causes of hypercalcemia including postoperative low albumin. A high PTH level was observed in 64 (20.8%) patients. We found 3 monoclonal bands. Results were similar in patients with and without vertebral fracture or osteoporosis. Finally, many biological abnormalities can be explained by the postoperative context (low TSH, hypogammaglobulinemia, low albumin, low alkaline phosphatase) and need a control.

CONCLUSION

This study performed in patient with recent low trauma non-vertebral fractures showed that 94.6% of patients had at least one contributor to bone fragility, which was the vitamin D insufficiency in most of cases. We found a high proportion of biological abnormalities which require additional explorations but most of them can be explained by the postoperative context.

[Hypophosphatasia : What is currently available for treatment?]

This review presents the current knowledge on the diagnosis and treatment of hypophosphatasia, a rare genetic disease, caused by mutations in the tissue non-specific alkaline phosphatase (TNSALP) gene. The clinical spectrum of hypophosphatasia is highly variable ranging from lethal infantile forms to mild forms diagnosed in adults. Although the disease rarely occurs, correct diagnosis is important to provide appropriate treatment and to avoid worsening by use of harmful drugs such as bisphosphonates. Low serum values of alkaline phosphatase (ALP) is the main feature of HPP, but by itself not sufficient for diagnosis, as it can occur under different conditions. Diagnosis can be established by the combination of reduced levels of ALP, elevated ALP substrates (PLP, PEA, PPi) and typical symptoms and can be confirmed by genetic testing of ALPL mutations. Enzyme replacement therapy is now available for affected patients with onset of the disease during childhood and adolescence. Early results of enzyme replacement therapy are encouraging. However, a multidisciplinary approach remains the core of the treatment including nutritional support, monitoring of vitamin D, calcium and phosphate levels, physical therapy and regular dental care.

Mutational and biochemical findings in adults with persistent hypophosphatasemia

A majority of adults with persistently low serum alkaline phosphatase values carry a pathogenic or likely pathogenic variant in the ALPL gene and also have elevated alkaline phosphatase substrate values in serum and urine. These adults may fall within the spectrum of the adult form of hypophosphatasia.

INTRODUCTION

The primary objective of this study was to determine what proportion of adults with persistently low serum alkaline phosphatase values (hypophosphatasemia) harbor mutations in the ALPL gene or have elevated alkaline phosphatase (ALP) substrates. Some adults with persistent hypophosphatasemia share clinical and radiographic features with the adult form of hypophosphatasia (HPP). In HPP, ALPL mutations result in persistent hypophosphatasemia and ALP substrate accumulation in plasma (pyridoxal-5-phosphate (PLP)) and urine (phosphoethanolamine (PEA)).

METHODS

Biochemical analyses, including serum ALP activity, bone-specific ALP, plasma PLP, and urine PEA, were performed in adults with persistent hypophosphatasemia. Mutational analyses were performed using PCR and Sanger sequencing methods. Gene variants were classified as pathogenic (P), likely pathogenic (LP), variants of uncertain significance (VUS), likely benign (LB), and benign (B). P and LP variants were further grouped as "Positive ALPL variants" and LB and B grouped as "Negative ALPL variants."

RESULTS

Fifty subjects completed all mutational and biochemical analyses. Sixteen percent carried only Negative ALPL variants. Of the remaining 42 subjects, 67% were heterozygous for a P variant, 19% for an LP variant, and 14% for a VUS. Biochemical results were highly inter-correlated and consistent with the expected inverse relationship between ALP and its substrates. Subjects harboring Positive ALPL variants showed lower ALP and BSAP and higher PLP and PEA values compared with subjects harboring only Negative ALPL variants. Approximately half of all subjects harboring Positive ALPL variants or ALPL VUS showed elevations in plasma PLP, and three quarters showed elevations in urine PEA.

CONCLUSION

Adults with persistent hypophosphatasemia frequently harbor ALPL mutations and have elevated ALP substrates. These adults may fall within the spectrum of the adult form of hypophosphatasia. Clinicians should take note of persistent hypophosphatasemia in their patients and be cautious in prescribing bisphosphonates when present.

Clinical, biochemical and genetic spectrum of low alkaline phosphatase levels in adults

BACKGROUND

Low serum levels of alkaline phosphatase (ALP) are a hallmark of hypophosphatasia. However, the clinical significance and the underlying genetics of low ALP in unselected populations are unclear.

METHODS

In order to clarify this issue, we performed a clinical, biochemical and genetic study of 42 individuals (age range 20-77yr) with unexplained low ALP levels.

RESULTS

Nine had mild hyperphosphatemia and three had mild hypercalcemia. ALP levels were inversely correlated with serum calcium (r=-0.38, p=0.012), pyridoxal phosphate (PLP; r=-0.51, p=0.001) and urine phosphoethanolamine (PEA; r=-0.49, p=0.001). Although many subjects experienced minor complaints, such as mild musculoskeletal pain, none had major health problems. Mutations in ALPL were found in 21 subjects (50%), including six novel mutations. All but one, were heterozygous mutations. Missense mutations were the most common (present in 18 subjects; 86%) and the majority were predicted to have a damaging effect on protein activity. The presence of a mutated allele was associated with tooth loss (48% versus 12%; p=0.04), slightly lower levels of serum ALP (p=0.002), higher levels of PLP (p<0.0001) and PEA (p<0.0001), as well as mildly increased serum phosphate (p=0.03). Ten individuals (24%) had PLP levels above the reference range; all carried a mutated allele.

CONCLUSION

One-half of adult individuals with unexplained low serum ALP carried an ALPL mutation. Although the associated clinical manifestations are usually mild, in approximately 50% of the cases, enzyme activity is low enough to cause substrate accumulation and may predispose to defects in calcified tissues.

Absence of recognition of low alkaline phosphatase level in a tertiary care hospital

SUMMARY

Low serum total alkaline phosphatase level (ALP), the hallmark for hypophosphatasia (HPP), must be recognized to provide appropriate care of the patients and to avoid antiresorptive treatment. The prevalence of persistent low ALP in a clinical setting is 0.13% and the recognition is very low (3%).

INTRODUCTION

A low serum total alkaline phosphatase level is the hallmark for the diagnosis of hypophosphatasia. Although very rare, HPP must be recognized to provide appropriate treatment of non-union fractures and to avoid potentially harmful drugs, such as antiresorptive treatments. The aim of this study was to assess the recognition of persistent low ALP in a tertiary care hospital.

METHODS

Between the 1st of January and the 31st of December 2013, 48,755 patients had ALP assessment in the Biochemistry Department of our hospital. Sixty-eight patients had all serum ALP values persistently below 40 IU/l. Among them, six had potential causes of secondary hypophosphatasia. We consulted the summary discharges of the 62 patients in order to check for the notation of low ALP. Patients from the departments of rheumatology and internal medicine were contacted to fulfill a questionnaire about clinical manifestations potentially related to HPP.

RESULTS

0.13% of hospitalized patients had persistently low value. They were 46.5 ± 17.7 years old, and 73% were females. The low ALP value was notified in the discharge summary for two patients (3%), without any comment. Twenty-four patients (46 + /-16 years old) were contacted. Eight patients had fractures; two had a diagnosis of rickets in the childhood; two had symptomatic chondrocalcinosis. Nine had dental abnormalities. Three were receiving a bisphosphonate; two of them had a fracture while being treated with bisphosphonate.

CONCLUSION

Our study shows that low ALP is not recognized in a clinical setting in adults hospitalized in a tertiary care hospital.

Osteonecrosis Secondary to Paget's Disease: Radiologic and Pathologic Features

Paget's disease (PD) is a chronic progressive disease of the bone characterized by abnormal bone metabolism affecting either a single bone (monostotic) or many bones (polyostotic) with uncertain etiology. We report a case of PD in a 70-year-old male, which was initially identified as osteonecrosis of the maxilla. Non-drug induced osteonecrosis in PD is rare and very few cases have been reported in the literature.

Clinical and radiographic findings in adults with persistent hypophosphatasemia

A serum alkaline phosphatase value below the age-adjusted lower limits of normal (hypophosphatasemia) is uncommonly encountered in clinical practice. The electronic and paper medical records of 885,165 patients treated between 2002 and 2012 at a large, rural, multispecialty health clinic were interrogated to estimate the prevalence and characterize the clinical and radiographic findings of adults whose serum alkaline phosphatase was almost always low (persistent hypophosphatasemia). We hypothesized that some of these patients might harbor previously unrecognized hypophosphatasia, a rare, inherited condition of impaired mineralization of bones and teeth. Persistent hypophosphatasemia (serum alkaline phosphatase ≤ 30 IU/L) was found in 1 of 1544 adult patients. These adult patients had more crystalline arthritis, orthopedic surgery, chondrocalcinosis, calcific periarthritis, enthesopathy, and diffuse idiopathic skeletal hyperostosis than a general adult patient population. A gender effect was observed. The clinical and radiographic findings of adult patients with persistent hypophosphatasemia resemble those of the adult form of hypophosphatasia. Clinicians should take notice of persistent hypophosphatasemia, consider the diagnosis of hypophosphatasia, and be cautious when considering potent anti-remodeling therapy in these adults. This population warrants further evaluation.