Alkaline Phosphatase Deficiency Research Articles

Tissue nonspecific alkaline phosphatase deficiency impairs Purkinje cell development and survival in a mouse model of infantile hypophosphatasia

Loss-of-function mutations in the tissue-nonspecific alkaline phosphatase (TNAP) gene can result in hypophosphatasia (HPP), an inherited multi-systemic metabolic disorder that is well-known for skeletal and dental hypomineralization. However, emerging evidence shows that both adult and pediatric patients with HPP suffer from cognitive deficits, higher measures of depression and anxiety, and impaired sensorimotor skills. The cerebellum plays an important role in sensorimotor coordination, cognition, and emotion. To date, the impact of TNAP mutation on the cerebellar circuitry development and function remains poorly understood. The main objective of this study was to investigate the roles of TNAP in cerebellar development and function, with a particular focus on Purkinje cells, in a mouse model of infantile HPP. Male and female wild type (WT) and TNAP knockout (KO) mice underwent behavioral testing on postnatal day 13–14 and were euthanized after completion of behavioral tests. Cerebellar tissues were harvested for gene expression and immunohistochemistry analyses. We found that TNAP mutation resulted in significantly reduced body weight, shorter body length, and impaired sensorimotor functions in both male and female KO mice. These developmental and behavioral deficits were accompanied by abnormal Purkinje cell morphology and dysregulation of genes that regulates synaptic transmission, cellular growth, proliferation, and death. In conclusion, inactivation of TNAP via gene deletion causes developmental delays, sensorimotor impairment, and Purkinje cell maldevelopment. These results shed light on a new perspective of cerebellar dysfunction in HPP.

Modern Approaches to the Management of Children with Hypophosphatasia

Hypophosphatasia is rare genetic disease caused by tissue-nonspecific alkaline phosphatase deficiency due to the mutation in the ALPL gene. Disease can manifest in utero, in childhood or in adults depending on its form and severity. This article presents modern data on the epidemiology, etiology, and clinical signs of hypophosphatasia in children, covers in details differential diagnostic search, and gives guidelines for its evidence-based treatment. Without timely treatment the prognosis of the disease is unfavorable in most cases. Such patients require follow-up by multidisciplinary team of physicians. The only effective method of treatment is enzyme replacement therapy with asfotase alfa. Symptomatic therapy is also crucial as well as physiotherapeutic procedures and therapeutic exercise programs (at rehabilitation stage).

Dental manifestations in adult hypophosphatasia and their correlation with biomarkers.

Hypophosphatasia (HPP) is a genetic condition with broad clinical manifestations caused by alkaline phosphatase (ALP) deficiency. Adults with HPP exhibit a wide spectrum of signs and symptoms. Dental manifestations including premature tooth loss are common. Much of the published literature reporting dental manifestations consists of case reports and series of symptomatic patients, likely biased towards more severe dental manifestations. The objective of this study was to systematically explore the dental manifestations among adults with HPP by conducting a comprehensive dental evaluation. To minimize bias, the study explored dental manifestations in an unselected cohort of adults with HPP. Participants were identified searching electronic health record (EHR) data from a rural health system to discover adults with persistent ALP deficiency. Heterozygotes with pathogenic (P), likely pathogenic (LP), or uncertain variants (VUS) in ALPL and at least one elevated ALP substrate were defined as adults with HPP and underwent genetic, dental, oral radiographic, and biomarker evaluation. Twenty‐seven participants completed the study. Premature tooth loss was present in 63% (17/27); 19% (5/27) were missing eight or more teeth. Statistically significant associations were found between premature permanent tooth loss and HPP biomarkers ALP (p = 0.049) and bone‐specific ALP (p = 0.006). Serum ALP (ρ = −0.43, p = 0.037) and bone‐specific ALP (ρ = −0.57, p = 0.004) were negatively correlated with number of teeth lost prematurely. As noted with tooth loss, periodontal breakdown was associated with bone‐specific ALP. An inverse association between periodontal breakdown and bone‐specific ALP was observed (p = 0.014). These findings suggest a role for ALP in maintenance of dentition.

Intestinal alkaline phosphatase deficiency increases the risk of diabetes

IntroductionOur previous case–control study demonstrated that a high level of intestinal alkaline phosphatase (IAP), an endotoxin-detoxifying anti-inflammatory enzyme secreted by villus-associated enterocytes and excreted with stool, plays a protective role...

ALPL Genotypes in Patients With Atypical Femur Fractures or Other Biochemical and Clinical Signs of Hypophosphatasia.

Hypophosphatasia (HPP) is a rare metabolic disorder caused by deficiency of alkaline phosphatase (ALP) enzyme activity, leading to defective mineralization, due to pathogenic variants of the ALPL gene, encoding the tissue nonspecific alkaline phosphatase (TNSALP) enzyme. Inheritance can be autosomal recessive or autosomal dominant. An abnormal ALPL genetic test enables accurate diagnosis, avoiding the administration of contraindicated antiresorptive drugs that, in patients with HPP, substantially increase the risk of atypical femur fractures (AFFs) and worsen the fracture healing process that is usually already compromised in these patients. Performing ALPL genetic testing to identify rare variants in suspected adult patients with HPP. Comparing frequencies of ALPL common variants in individuals with biochemical and/or clinical signs suggestive of adult HPP and non-HPP controls, and among different clinical subgroups of patients with a clinical suspicion of adult HPP. Patients with suspected adult HPP were retrospectively selected for the genetic testing of the ALPL gene. Patients included were from 3 main European Bone Units (Florence, Naples, and Geneva); 106 patients with biochemical and/or clinical signs suggestive of a mild form of HPP were included. Genetic testing led to the identification of a heterozygote rare variant in 2.8% of cases who were initially referred as suspected osteoporosis. The analysis of frequencies of ALPL common variants showed a high prevalence (30.8%) of homozygosity in subjects who developed an AFF, in association with normal serum total ALP activity. The results suggest homozygosity of common ALPL variants as a possible genetic mark of risk for these fractures.

Perinatal hypophosphatasia

Hypophosphatasia, also known as alkaline phosphatase deficiency, is a rare congenital metabolic disorder characterised by early bone and dental defects. First reports on hypophosphatasia date back to 1950s. The prevalence of the disorder in Europe is 1:300,000 births; data on the prevalence in Poland is missing. An abnormal structure of the region coding for the ALPL gene, which is responsible for producing tissue-nonspecific alkaline phosphatase, is the main cause of clinical symptoms. Consequently, there is a significant deficiency in the activity or even absence of this enzyme. Due to the heterogeneous clinical expression of hypophosphatasia, multiple clinical forms of the disorder, which vary in their mode of inheritance and prognosis, have been described, including rare and sporadically reported perinatal forms. There are ongoing studies on the aetiology, diagnosis and treatment of different clinical forms of hypophosphatasia. We present a case report of perinatal hypophosphatasia diagnosed in the Department of Neonatology at the University Clinical Hospital in Wroclaw, with particular focus on the implemented diagnostic-therapeutic process and possible complications in the affected child during the stay in the neonatal intensive care unit. We also performed a literature review to present a wider picture of the disorder belonging to the group of the so-called rare diseases. We described current diagnostic and treatment possibilities in hypophosphatasia, based on the latest clinical trials, as well as the costs of treatment using Strensiq, the only alkaline phosphatase analogue available on the market.

MON-341 New Diagnosis of Hypophosphatasia in a 79-Year-Old Woman with Low Bone Density

Introduction: Hypophosphatasia is a rare metabolic bone disease caused by one of several mutations in the ALPL gene which encodes tissue nonspecific alkaline phosphatase (ALP). It is usually diagnosed in childhood and can have a heterogenous clinical presentation depending on the extent of enzyme deficiency. Here we report the oldest known patient with hypophosphatasia. Clinical Case: A 79-year-old woman with a history of medullary thyroid cancer (MTC) in remission, was referred to our metabolic bone disease clinic for the evaluation and treatment of osteopenia. She had suffered from numerous musculoskeletal complaints for several years and had received a diagnosis of polymyalgia rheumatica. However, her symptoms persisted despite a six month trial of prednisone. Although she had developed dental caries at a young age, she denied premature tooth loss. Her family history was significant for arthralgias and vertebral disc disorders in multiple family members, including both her children. Her mother carried a diagnosis of rheumatoid arthritis and osteoporosis. The only pertinent physical exam finding was short stature (Height -4’6”). A DEXA scan was performed using a Hologic unit and revealed a T Score of -1.0 at the L-spine and -1.9 at the femoral neck. A FRAX score predicted a 14% risk of major osteoporotic fracture and 4% risk of hip fracture.Laboratory data revealed: Serum Calcium 9.3 (8.5-10.5 mg/dL), Albumin 4.3 (3.5-5.0 g/dL), ALP 21 (<130 U/L), Vitamin D 25OH 46.2 (>30 ng/ml), Intact PTH 28.3 (15.0-65.0 pg/ml), Vitamin B6 87.7 (2-21 ng/ml).On review of her medical record, low ALP levels ranging between 20-30 U/L were noted to be present for the last twenty years. Given her history of musculoskeletal complaints, short stature, elevated Vitamin B6 and low ALP, genetic testing for hypophosphatasia was performed. Her results confirmed a known pathogenic mutation in the ALPL gene. Conclusion: This case highlights the importance of reviewing ALP levels and relevant patient history to rule out hypophosphatasia prior to initiating therapy for osteoporosis. This condition is often unrecognized. Bisphosphonates, which are often the first line of treatment in osteoporosis, are contraindicated in hypophosphatasia as they can increase the risk of atypical fractures.1 Teriparatide may improve bone density depending on the extent of ALP deficiency. Asfotase alfa is a new agent that is currently available for the management of certain cases of hypophosphatasia.

Intestinal Alkaline Phosphatase Deficiency Is Associated with Ischemic Heart Disease.

Background We have previously shown that the deficiency of the gut enzyme intestinal alkaline phosphatase (IAP) is associated with type 2 diabetes mellitus (T2DM) in humans, and mice deficient in IAP develop the metabolic syndrome, a precipitant of T2DM and ischemic heart disease (IHD). We hypothesized that IAP deficiency might also be associated with IHD in humans. We aimed to determine the correlation between the IAP level and IHD in humans. Methods and Results The IHD patients were recruited from the National Institute of Cardiovascular Diseases (NICVD), Dhaka, Bangladesh, and the control healthy participants were recruited from a suburban community of Dhaka. We determined the IAP level in the stools of 292 IHD patients (187 males, 105 females) and 331 healthy control people (84 males, 247 females). We found that compared to controls, IHD patients have approx. 30% less IAP (mean ± SEM: 63.7 ± 3.5 vs. 44.9 ± 2.1 U/g stool, respectively; p < 0.000001), which indicates that IAP deficiency is associated with IHD, and a high level of IAP is probably protective against IHD in humans. The adjusted generalized linear model (GLM) of regression analysis predicted a strong association of IAP with IHD (p = 0.0035). Multiple logistic regression analysis showed an independent inverse relationship between the IAP level and the IHD status (odds ratio, OR = 0.993 with 95% CI 0.987-0.998; p < 0.01). Conclusions IAP deficiency is associated with IHD, and a high level of IAP might be protective against IHD.

Alkaline Phosphatase Treatment of Acute Kidney Injury in an Infant Piglet Model of Cardiopulmonary Bypass with Deep Hypothermic Circulatory Arrest

Acute kidney injury (AKI) is associated with prolonged hospitalization and mortality following infant cardiac surgery, but therapeutic options are limited. Alkaline phosphatase (AP) infusion reduced AKI in phase 2 sepsis trials but has not been evaluated for cardiac surgery-induced AKI. We developed a porcine model of infant cardiopulmonary bypass (CPB) with deep hypothermic circulatory arrest (DHCA) to investigate post-CPB/DHCA AKI, measure serum/renal tissue AP activity with escalating doses of AP infusion, and provide preliminary assessment of AP infusion for prevention of AKI. Infant pigs underwent CPB with DHCA followed by survival for 4 h. Groups were treated with escalating doses of bovine intestinal AP (1, 5, or 25U/kg/hr). Anesthesia controls were mechanically ventilated for 7 h without CPB. CPB/DHCA animals demonstrated histologic and biomarker evidence of AKI as well as decreased serum and renal tissue AP compared to anesthesia controls. Only high dose AP infusion significantly increased serum or renal tissue AP activity. Preliminary efficacy evaluation demonstrated a trend towards decreased AKI in the high dose AP group. The results of this dose-finding study indicate that AP infusion at the dose of 25U/kg/hr corrects serum and tissue AP deficiency and may prevent AKI in this piglet model of infant CPB/DHCA.

Frequency and age at occurrence of clinical manifestations of disease in patients with hypophosphatasia: a systematic literature review

BackgroundHypophosphatasia (HPP) is a rare, inherited, metabolic disease caused by tissue-nonspecific alkaline phosphatase deficiency, characterized by bone mineralization defects and systemic complications. Understanding of the clinical course and burden of HPP is limited by its rarity. This systematic literature review and synthesis of case report data aimed to determine the frequency and timing of clinical HPP manifestations and events.MethodsCase reports and series of patients with HPP who had been followed longitudinally for ≥1 year were identified. Demographics and clinical data of interest, identified through consultation with clinical experts in HPP, were extracted. Occurrences of clinical manifestations/events of interest were categorized, classified by age at first reported occurrence of HPP manifestations and visualized over time. Clinical manifestations/events considered to contribute to the clinical burden of HPP were identified. Kaplan–Meier curves were used to estimate the median (range) age at first occurrence of the most frequently reported manifestations/events.ResultsFrom the 283 studies that met the inclusion criteria, 265 patients with HPP with ≥1 year of longitudinal follow-up were identified (median [interquartile range] age 4 [0–34] years; 45% male). The types of clinical manifestations/events of interest experienced by individuals with ≥1 such manifestation/event (n = 261) often differed between older and younger patients. Most (94%) of the 265 patients experienced ≥1 manifestation/event deemed to contribute to the clinical burden of HPP; premature tooth loss (53.5%), fractures (35.8%), pain (33.6%), and gross motor/ambulation difficulties (30.9%) were most frequently reported. The median (range) age at first reported occurrence of respiratory symptoms, cranial abnormalities, and premature tooth loss ranged from 0.3 to 10 years, whereas the median age at first reported occurrence of fractures, pain, gross motor/ambulation difficulties, and surgery ranged from 33 to 70 years.ConclusionsHPP is associated with a high clinical burden of disease, regardless of age at first reported occurrence of HPP manifestations. Over an individual’s lifetime, the types of manifestations/events experienced can change and multiple HPP-related clinical manifestations/events can accumulate. These observations may reflect evolution and progression of the disease.

MON-495 Hypophosphatasia: A Rare Cause of Osteoporosis in a Young Adult Male

Introduction: Secondary osteoporosis is due to an identifiable cause of osteoporosis. Hypophosphatasia is a rare cause of secondary osteoporosis and needs to be considered when evaluating osteoporosis in young people. We present a case of secondary osteoporosis initially thought to be a result of malabsorptive disorder and chronic steroid use, with eventual diagnosis of autosomal dominant hypophosphatasia as the primary underlying cause. Clinical Case: A 24 year old male who was seen for evaluation of osteoporosis. He reported an extensive history of fractures about 26 in total, including wrist, shoulders, nose, and metatarsals. Past history was also significant for bowed legs at birth requiring osteotomies and spontaneous loss of several teeth with root intact, requiring extractions. He was also diagnosed with Crohn’s disease at 17 years old and history of steroid use, however was not on steroids at time of initial evaluation. He was diagnosed with bilateral avascular necrosis at age 18 years and needed bilateral hip replacement at age 20 years. There was no family history of skeletal disorders. DEXA scan obtained for the assessment of bone density revealed a Z score of -2.6 in the lumbar spine and -2.1 in the distal forearm. Further evaluation for secondary causes of osteoporosis revealed a normal TSH, PTH, tryptase, vitamin D and testosterone levels. Bone turnover markers were normal except for a low alkaline phosphatase. It was noted that the patient had a persistently low alkaline phosphatase for the last 6 years despite his frequent fractures. Hypophosphatasia was suspected given the history and the low alkaline phosphatase levels. Pyridoxal 5-phosphate was elevated at 77mcg/L (normal 5-50mcg/L). Genetics evaluation revealed a heterozygous, missense mutation in ALPL gene, confirming diagnosis of autosomal dominant hypophosphatasia. He was started on enzyme replacement therapy with asfotase alpha. Conclusion: Hypophosphatasia is a rare metabolic bone disease due to a deficiency of alkaline phosphatase which may present from infancy to adulthood. Diagnosis is made by finding a low alkaline phosphatase level and elevated 5 pyridoxal phosphate. Enzyme replacement therapy with asfotase alpha is the mainstay of treatment. It is probably underdiagnosed secondary to its rarity and therefore must be considered in any young patient who presents with osteoporosis.

SUN-529 Burden of Illness in Adults with Hypophosphatasia: Data From the Global Hypophosphatasia Patient Registry

Background: Hypophosphatasia (HPP) is a rare, systemic, metabolic disease caused by tissue-nonspecific alkaline phosphatase deficiency, characterized by poor skeletal mineralization, muscle weakness and ambulatory difficulties. Limited data are available on the burden of illness in adults with HPP. Methods: Data from the Global HPP Patient Registry were used to identify adults (≥ 18 years old) who had a diagnosis of HPP (confirmed by low serum alkaline phosphatase activity for age and sex and/or an ALPL pathogenic variant) and who had never been treated with asfotase alfa (AA). The following components of disease burden were assessed in these patients: occurrence of clinical HPP manifestations, number of body systems affected by HPP manifestations, number of fractures/pseudofractures and use of pain medication. Patient-reported pain (assessed by the Brief Pain Inventory Short Form [BPI-SF]; scale 0 to 10; higher scores represent higher levels of pain), disability (assessed by the Health Assessment Questionnaire Disability Index [HAQ-DI]; scale 0 to 3; higher scores represent more severe disability) and quality of life (QoL; assessed by the 36-item Short-Form Health Survey version 2 [SF-36v2]; scale 0 to 100; higher scores indicate better QoL) were analyzed in relation to the number of HPP manifestations experienced. Results: Of the 218 adult patients (74% female) included in this analysis, mean (standard deviation [SD]) age at HPP diagnosis was 41.0 (18.8) years. Most patients had adult-onset (50%) or pediatric-onset (38%) HPP (33% and 5% of patients had juvenile- or infantile-onset HPP, respectively); age of onset was unknown for 12% of patients. The most common clinical HPP manifestations were chronic bone pain (60% of patients), generalized body pain (41%), and recurrent and poorly healing fractures (33%); 58% of patients had at least one fracture/pseudofracture (mean [SD] = 2.8 [2.6] per patient). Most patients (52%) had at least five clinical HPP manifestations, and 34% had manifestations in at least five body systems. Use of pain medication was reported in 41% of patients, 48% of whom were receiving opioids. Median self-reported pain scores on the BPI-SF were 3.6 (0-9.5) for pain severity and 3.1 (0-9.4) for pain interference in daily activities. Mean (SD) disability measured on the HAQ-DI was 0.5 (0.6). The mean (SD) physical component summary score of the SF-36v2 was 41.8 (10.8) and the mean (SD) mental component summary score was 45.6 (10.1); both scores were lower than the mean among the general population (50.0). There were significant correlations between greater numbers of HPP manifestations experienced and poorer scores on the BPI-SF, HAQ-DI and SF-36v2 (all p < 0.05). Conclusion: Adults with HPP who have never been treated with AA often experience pain and have a substantial burden of illness which can impact patient-reported QoL.

Intestinal alkaline phosphatase deficiency leads to dysbiosis and bacterial translocation in the newborn intestine

BackgroundIntestinal alkaline phosphatase (IAP) has been shown to help maintain intestinal homeostasis. Decreased expression of IAP has been linked with pediatric intestinal diseases associated with bacterial overgrowth and subsequent inflammation. We hypothesize that the absence of IAP leads to dysbiosis, with increased inflammation and permeability of the newborn intestine. MethodsSprague–Dawley heterozygote IAP cross-matches were bred. Pups were dam fed ad lib and euthanized at weaning. The microbiotas of terminal ileum (TI) and colon was determined by quantitative real-time polymerase chain reaction (qRT-PCR) of subphylum-specific bacterial 16S ribosomal RNA. RT-PCR was performed on TI for inflammatory cytokines. Intestinal permeability was quantified by fluorescein isothiocyanate–dextran permeability and bacterial translocation by qRT-PCR for bacterial 16S ribosomal RNA in mesenteric lymph nodes. Statistical analysis was done by chi-square analysis. ResultsAll three genotypes had similar concentrations of bacteria in the TI and colon. However, IAP knockout (IAP-KO) had significantly decreased diversity of bacterial species in their colonic stool compared with heterozygous and wild-type (WT). IAP-KO pups had a nonstatistically significant 3.9-fold increased inducible nitric oxide synthase messenger RNA expression compared with WT (IAP-KO, 3.92 ± 1.36; WT, 1.0 ± 0.27; P = 0.03). IAP-KO also had significantly increased bacterial translocation to mesenteric lymph nodes occurred in IAP-KO (IAP-KO, 7625 RFU/g ± 3469; WT, 4957 RFU/g ± 1552; P = 0.04). Furthermore, IAP-KO had increased permeability (IAP-KO, 0.297 mg/mL ± 0.2; WT, 0.189 mg/mL ± 0.15 P = 0.07), but was not statistically significant. ConclusionsDeficiency of IAP in the newborn intestine is associated with dysbiosis and increased inflammation, permeability, and bacterial translocation.

Case series: Odontohypophosphatasia or missed diagnosis of childhood/adult-onset hypophosphatasia? – Call for a long-term follow-up of premature loss of primary teeth

IntroductionHypophosphatasia, a metabolic bone disease caused by a tissue-nonspecific alkaline phosphatase deficiency, leads to undermineralization of bone and/or teeth, impaired vitamin B6 metabolism, and a spectrum of disease presentation. At the mild end of the spectrum, it presents as pathologic fractures in later adulthood. Patients with isolated dental manifestations, typically presenting as premature loss of primary teeth, are classified as having odontohypophosphatasia (odontoHPP). A subset of patients diagnosed with odontoHPP in childhood can later develop extra-dental manifestations that constitute childhood- or adult-onset hypophosphatasia. Case reports: methods/resultsRetrospective data related to onset, detailed clinical course, and method of diagnosis were collected as part of a natural history of adult patients with hypophosphatasia.Of 9 initial patients, all had low serum alkaline phosphatase levels for their age and gender at adult presentation (Table 2). The majority (8/9) demonstrated childhood dental signs of hypophosphatasia as the initial clinical manifestation: premature loss of primary teeth (7/9), absent primary teeth (1/9), and delayed loss of primary teeth (1/9). Despite childhood dental presentation and/or other signs/symptoms, diagnosis of hypophosphatasia was delayed 20–54years (median=46) since the primary tooth problems and 8–45years (median=27) since the first fracture or onset of a major adult tooth problem. ConclusionPatients with primary tooth loss in childhood were often diagnosed with hypophosphatasia later in life. Pediatric patients classified as having odontoHPP under present practice can manifest significant disease burden later in life.

Intestinal Alkaline Phosphatase Deficiency Leads to Dysbiosis and Bacterial Translocation in the Newborn Intestine

Intestinal Alkaline Phosphatase Deficiency Leads to Dysbiosis and Bacterial Translocation in the Newborn Intestine

Intestinal alkaline phosphatase deficiency leads to lipopolysaccharide desensitization and faster weight gain.

Animals develop in the presence of complex microbial communities, and early host responses to these microbes can influence key aspects of development, such as maturation of the immune system, in ways that impact adult physiology. We previously showed that the zebrafish intestinal alkaline phosphatase (ALPI) gene alpi.1 was induced by Gram-negative bacterium-derived lipopolysaccharide (LPS), a process dependent on myeloid differentiation primary response gene 88 (MYD88), and functioned to detoxify LPS and prevent excessive host inflammatory responses to commensal microbiota in the newly colonized intestine. In the present study, we examined whether the regulation and function of ALPI were conserved in mammals. We found that among the mouse ALPI genes, Akp3 was specifically upregulated by the microbiota, but through a mechanism independent of LPS or MYD88. We showed that disruption of Akp3 did not significantly affect intestinal inflammatory responses to commensal microbiota or animal susceptibility to Yersinia pseudotuberculosis infection. However, we found that Akp3(-/-) mice acquired LPS tolerance during postweaning development, suggesting that Akp3 plays an important role in immune education. Finally, we demonstrated that inhibiting LPS sensing with a mutation in CD14 abrogated the accelerated weight gain in Akp3(-/-) mice receiving a high-fat diet, suggesting that the weight gain is caused by excessive LPS in Akp3(-/-) mice.

Tissue-nonspecific alkaline phosphatase deficiency causes abnormal craniofacial bone development in the Alpl−/− mouse model of infantile hypophosphatasia

Tissue-nonspecific alkaline phosphatase (TNAP) is an enzyme present on the surface of mineralizing cells and their derived matrix vesicles that promotes hydroxyapatite crystal growth. Hypophosphatasia (HPP) is an inborn-error-of-metabolism that, dependent upon age of onset, features rickets or osteomalacia due to loss-of function mutations in the gene (Alpl) encoding TNAP. Craniosynostosis is prevalent in infants with HPP and other forms of rachitic disease but how craniosynostosis develops in these disorders is unknown. ObjectivesBecause craniosynostosis carries high morbidity, we are investigating craniofacial skeletal abnormalities in Alpl−/− mice to establish these mice as a model of HPP-associated craniosynostosis and determine mechanisms by which TNAP influences craniofacial skeletal development. MethodsCranial bone, cranial suture and cranial base abnormalities were analyzed by micro-CT and histology. Craniofacial shape abnormalities were quantified using digital calipers. TNAP expression was suppressed in MC3T3E1(C4) calvarial cells by TNAP-specific shRNA. Cells were analyzed for changes in mineralization, gene expression, proliferation, apoptosis, matrix deposition and cell adhesion. ResultsAlpl−/− mice feature craniofacial shape abnormalities suggestive of limited anterior–posterior growth. Craniosynostosis in the form of bony coronal suture fusion is present by three weeks after birth. Alpl−/− mice also exhibit marked histologic abnormalities of calvarial bones and the cranial base involving growth plates, cortical and trabecular bone within two weeks of birth. Analysis of calvarial cells in which TNAP expression was suppressed by shRNA indicates that TNAP deficiency promotes aberrant osteoblastic gene expression, diminished matrix deposition, diminished proliferation, increased apoptosis and increased cell adhesion. ConclusionsThese findings demonstrate that Alpl−/− mice exhibit a craniofacial skeletal phenotype similar to that seen in infants with HPP, including true bony craniosynostosis in the context of severely diminished bone mineralization. Future studies will be required to determine if TNAP deficiency and other forms of rickets promote craniosynostosis directly through abnormal calvarial cell behavior, or indirectly due to deficient growth of the cranial base.

Hypophosphatasia Presenting with Pyridoxine-Responsive Seizures, Hypercalcemia, and Pseudotumor Cerebri: Case Report

Hypophosphatasia (HPP) is an inborn error of metabolism characterized by defective bone mineralization caused by a deficiency in alkaline phosphatase (ALP) activity due to mutations in the tissue-nonspecific ALP (TNALP) gene. The clinical expression of the disease is variable. Six forms of HPP are identified according to age at presentation and clinical features. Patients with the infantile form are normal at birth. First symptoms appear within the first 6 months of life. Along with skeletal findings, HPP patients may present with hypercalcemia, seizures, pseudotumor cerebri, and pulmonary insufficiency. Seizures in HPP are refractory to conventional antiepileptic drugs, but are responsive to pyridoxine. Herein, we report a case of HPP who presented with pyridoxine-responsive seizures in the early neonatal period and was found to have hypercalcemia, skeletal demineralization and increased intracranial pressure. Key words: Hypophosphatasia, pyridoxine-responsive seizures, bisphosphonates, alkaline phosphatase, bone resorption, hypercalcemia Conflict of interest:None declared.

Intramedullary Nailing for Adult Hypophosphatasia: A Case Report

Hypophosphatasia is a rare genetic metabolic disorder characterised by defective bone mineralisation secondary to serum and bone alkaline phosphatase deficiency. We report a 46-year-old woman who underwent multiple intramedullary nailings for fractures and deformities of 6 long bones over 13 years.

Infantile Hypophosphatasia due to a New Compound Heterozygous TNSALP Mutation – Functional Evidence for a Hydrophobic Side-Chain?

Infantile hypophosphatasia (IH) is an inherited disorder characterized by defective bone mineralization and a deficiency of alkaline phosphatase activity. The aim of the study was to evaluate a new compound heterozygous TNSALP mutation for its residual enzyme activity and localization of the comprised amino acid residues in a 3D-modeling. We report on a 4-week old girl with craniotabes, severe defects of ossification, and failure to thrive. Typical clinical features as low serum alkaline phosphatase, high serum calcium concentration, increased urinary calcium excretion, and nephrocalcinosis were observed. Vitamin D was withdrawn and the patient was started on calcitonin and hydrochlorothiazide. Nonetheless, the girl died at the age of 5 months from respiratory failure. Sequence analysis of the patient's TNSALP gene revealed two heterozygous mutations [c.653T>C (I201T), c.1171C>T (R374C)]. Transfection studies of the unique I201T variant in COS-7 cells yielded a mutant TNSALP protein with only a residual enzyme activity (3.7%) compared with wild-type, whereas the R374C variant was previously shown to reduce normal activity to 10.3%. 3D-modeling of the mutated enzyme showed that I201T resides in a region that does not belong to any known functional site. We note that I201, which has been conserved during evolution, is buried in a hydrophobic pocket and, therefore, the I>T-change should affect its functional properties. Residue R374C is located in the interface between monomers and it has been previously suggested that this mutation affects dimerization. These findings explain the patient's clinical picture and severe course.