Odontohypophosphatasia caused by a novel combination of two heterozygous variants: a case report.

Hypophosphatasia (HPP) is a rare genetic disorder mainly characterized by skeletal dysplasia that results from a deficiency in tissue-nonspecific alkaline phosphatase (TNSALP), which is encoded by the alkaline phosphatase (ALPL) gene. Odontohypophosphatasia (odonto-HPP) is a mild form of HPP characterized by oral symptoms, such as premature loss of primary teeth. This study was to describe a 4-year-old boy with premature loss of primary teeth who was diagnosed with odonto-HPP. X-ray radiography and laboratory examinations were performed for the diagnosis. Genetic etiology was revealed by whole-exome sequencing. A novel combination of two variants in the ALPL gene was identified in this case; this combination resulted in the odonto-HPP phenotype. c.346G>A (p.Ala116Thr) was inherited from the proband's father, whereas c.1563C>G (p.Ser521Arg) was inherited from the proband's mother. The proband's 8-year-old sister was a heterozygous carrier of c.346G>A (p.Ala116Thr) in the ALPL gene. Thus far, the proband's sister has been asymptomatic. Our findings indicate that c.346G>A is a pathogenic genetic alteration; c.1563C>G might cause a predisposition to the dental phenotype in combination with c.346G>A. It is important for pediatric dentists to consider a diagnosis of odonto-HPP in children with premature loss of primary teeth.

Hypophosphatasia: A Unique Disorder of Bone Mineralization.

Hypophosphatasia (HPP) is a rare genetic disease characterized by a decrease in the activity of tissue non-specific alkaline phosphatase (TNSALP). TNSALP is encoded by the ALPL gene, which is abundantly expressed in the skeleton, liver, kidney, and developing teeth. HPP exhibits high clinical variability largely due to the high allelic heterogeneity of the ALPL gene. HPP is characterized by multisystemic complications, although the most common clinical manifestations are those that occur in the skeleton, muscles, and teeth. These complications are mainly due to the accumulation of inorganic pyrophosphate (PPi) and pyridoxal-5'-phosphate (PLP). It has been observed that the prevalence of mild forms of the disease is more than 40 times the prevalence of severe forms. Patients with HPP present at least one mutation in the ALPL gene. However, it is known that there are other causes that lead to decreased alkaline phosphatase (ALP) levels without mutations in the ALPL gene. Although the phenotype can be correlated with the genotype in HPP, the prediction of the phenotype from the genotype cannot be made with complete certainty. The availability of a specific enzyme replacement therapy for HPP undoubtedly represents an advance in therapeutic strategy, especially in severe forms of the disease in pediatric patients.

A novel combination of biallelic ALPL mutations associated with adult hypophosphatasia: A phenotype-genotype association and computational analysis study.

Hypophosphatasia (HPP) is an inherited metabolic disorder that causes defective skeletal and dental mineralization. HPP exhibits a markedly heterogeneous range of clinical manifestations caused by dysfunction of the tissue-nonspecific isozyme of alkaline phosphatase (TNSALP), resulting from loss-of-function mutations in the ALPL gene. HPP has been associated with predominantly missense mutations in ALPL, and a number of compound heterozygous genotypes have been identified. Here, we describe a case of a subject with adult-onset HPP caused by a novel combination of missense mutations p.Gly473Ser and p.Ala487Val, resulting in chronic musculoskeletal pain, myopathy, persistent fatigue, vomiting, and an uncommon dental phenotype of short-rooted permanent teeth. Pedigree and biochemical analysis indicated that severity of symptoms was correlated with levels of residual ALP activity, and co-segregated with the p.Gly473Ser missense mutation. Bioinformatic analysis to predict the structural and functional impact of each of the point mutations in the TNSALP molecule, and its potential contribution to the clinical symptoms, revealed that the affected Gly473 residue is localized in the homodimer interface and predicted to have a dominant negative effect. The affected Ala487 residue was predicted to bind to Tyr479, which is closely located the N-terminal α-helix of TNSALP monomer 2, suggesting that both changes may impair dimer stability and catalytic functions. In conclusion, these findings assist in defining genotype-phenotype associations for HPP, and further define specific sites within the TNSALP molecule potentially related to neuromuscular manifestations in adult HPP, allowing for a better understanding of HPP pathophysiology.

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

BACKGROUND: Hypophosphatasia (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. METHODS: Case 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. RESULTS: From 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. CONCLUSIONS: HPP 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.

Caso clínico: hipofosfatasia de la niñez. Seguimiento clínico / Clinical case: childhood hypophosphatasia. Clinical follow-up

La hipofosfatasia (HP) es una enfermedad congénita, causada por mutaciones con pérdida de función en el gen ALPL que codifica la isoenzima no específica de tejido de la fosfatasa alcalina (TNSALP). Su expresión clínica es muy variable, desde casos de muerte intraútero por alteración grave de la mineralización ósea, hasta casos solo con caída prematura de la dentición. Se presenta el caso clínico de un varón al que se le diagnosticó odontohipofosfatasia a los 30 meses por pérdida temprana de piezas dentarias y niveles anormalmente bajos de fosfatasa alcalina, sin signos de raquitismo ni deformidades óseas. Durante su seguimiento, hasta los 13 años, presentó síntomas compatibles con HP infantil leve, como cansancio al caminar, incoordinación en la marcha y dolor en miembros inferiores que aumentaban con la actividad física. Ante la aparición de edema bimaleolar y poca respuesta al tratamiento con calcitonina y antiinflamatorios, se descartaron patologías infecciosas o reumáticas o ambas y se diagnosticó, por biopsia de tibia y peroné, periostitis sin detección de cristales de pirofosfato. Los controles radiológicos durante su evolución mostraron ensanchamiento metafisario en muñeca, falta de remodelado de metacarpianos, hojaldrado perióstico en tibia y peroné e hipomineralización en metáfisis tibiales, con "lenguas radiolúcidas" características de HP. Como conclusión, la hipofosfatasia debe considerarse como una entidad clínica para descartar en niños que presentan pérdida temprana de dientes. La presencia de este cuadro clínico es en general suficiente para realizar el diagnóstico de HP de la niñez. (AU)

Hypophosphatasia (HP) is a congenital disease, caused by mutations with loss of function in the gene ALPL that encodes the non-specific tissue isoenzyme of alkaline phosphatase (TNSALP). Its clinical expression displays considerable variability, from cases of intrauterine death due to severe alteration of bone mineralization, to cases with only early loss of teeth. We report the case of a male, diagnosed as odontohypophosphatasia at 30 months of age due to early loss of teeth and abnormally low levels of alkaline phosphatase, without signs of rickets or bone deformities. During follow-up, up to 13 years of age, he presented symptoms consistent with mild infantile HP such as tiredness when walking, lack of gait coordination, and pain in lower limbs, especially after physical activity. Due to the appearance of bimalleolar edema and poor response to treatment with calcitonin and anti-inflammatory drugs, infectious and / or rheumatic pathologies were ruled out. Periostitis without pyrophosphate crystal detection was diagnosed by tibial and fibular biopsy. Radiological controls during follow up showed metaphyseal wrist enlargement, lack of remodeling of metacarpals, periosteal flaking in the tibia and fibula and hypomineralization in the tibial metaphysis, with "radiolucent tongues"; characteristic of HP. In conclusion, hypophosphatasia should be considered as a clinical entity in children who present early loss of teeth. The presentation of this clinical case is generally sufficient to make the diagnosis of childhood HP. (AU)

Hypophosphatasia in Adults: Clinical Assessment and Treatment Considerations.

Hypophosphatasia (HPP) is a rare inherited disorder of bone affecting approximately 500 to 600 known individuals in the United States. HPP is the result of mutations involving the gene for tissue nonspecific alkaline phosphatase. Five clinical types of HPP are recognized. The clinical presentation of HPP varies from devastating prenatal intrauterine disease to mild manifestations in adulthood. In adults, main clinical involvement includes early loss of primary or secondary teeth, osteoporosis, bone pain, chondrocalcinosis, and fractures. Treatment for HPP is limited. Asfotase alfa is a subcutaneously administered synthetic human alkaline phosphatase that is approved for treatment of patients, including adults, with perinatal/infantile- and juvenile-onset HPP. However, guidelines for the treatment of adults with HPP are not available. This discussion addresses diagnostic and treatment considerations for adults with HPP. © 2017 American Society for Bone and Mineral Research.

Hypophosphatasia: An overview For 2017.

Hypophosphatasia (HPP) is the inborn-error-of-metabolism that features low serum alkaline phosphatase (ALP) activity (hypophosphatasemia) caused by loss-of-function mutation(s) of the gene that encodes the tissue-nonspecific isoenzyme of ALP (TNSALP). Autosomal recessive or autosomal dominant inheritance from among >300 TNSALP (ALPL) mutations largely explains HPP's remarkably broad-ranging severity. TNSALP is a cell-surface homodimeric phosphohydrolase richly expressed in the skeleton, liver, kidney, and developing teeth. In HPP, TNSALP substrates accumulate extracellularly. Among them is inorganic pyrophosphate (PPi), a potent inhibitor of mineralization. Superabundance of extracellular PPi explains the hard tissue complications of HPP that feature premature loss of deciduous teeth and often rickets or osteomalacia as well as calcific arthropathies in some affected adults. In infants with severe HPP, blocked entry of minerals into the skeleton can cause hypercalcemia, and insufficient hydrolysis of pyridoxal 5'-phosphate (PLP), the major circulating form of vitamin B6, can cause pyridoxine-dependent seizures. Elevated circulating PLP is a sensitive and specific biochemical marker for HPP. Also, the TNSALP substrate phosphoethanolamine (PEA) is usually elevated in serum and urine in HPP, though less reliably for diagnosis. Pathognomonic radiographic changes occur in pediatric HPP when the skeletal disease is severe. TNSALP mutation analysis is essential for recurrence risk assessment for HPP in future pregnancies and for prenatal diagnosis. HPP was the final rickets/osteomalacia to have a medical treatment. Now, significant successes using asfotase alfa, a mineral-targeted recombinant TNSALP, are published concerning severely affected newborns, infants, and children. Asfotase alfa was approved by regulatory agencies multinationally in 2015 typically for pediatric-onset HPP.

Hypophosphatasia: Natural history study of 101 affected children investigated at one research center.

Hypophosphatasia (HPP) is the inborn-error-of-metabolism that features deficient activity of the tissue-nonspecific isoenzyme of alkaline phosphatase (TNSALP). Resultant extracellular accumulation of inorganic pyrophosphate, a TNSALP substrate and potent inhibitor of mineralization, typically leads to tooth loss and sometimes to rickets or osteomalacia. HPP's remarkably broad-ranging severity is largely explained by autosomal dominant versus autosomal recessive transmission from among several hundred usually missense mutations positioned throughout the gene that encodes TNSALP. In 2015, our cross-sectional investigation of 173 affected children validated and expanded the clinical nosology commonly used for pediatric HPP. Herein, for the 101 patients in that cohort with longitudinal data, we explored the natural history of pediatric HPP by assessing their z-scores for height and then for weight, grip strength, and bone mineral density (BMD) determined by dual energy X-ray absorptiometry (DXA) also after adjusting for patient height. Eighteen patients contributed to "across" puberty evaluation. According to increasing HPP severity, there were 28 odonto HPP, 28 mild childhood HPP, 37 severe childhood HPP, and 8 infantile HPP patients typically studied from early to mid-childhood. The individual values for each parameter were wide-ranging within, and overlapping between, the four successive patient groups. Final mean/median z-scores, like the published initial values, paralleled the nosology. Longitudinal findings were similar for the boys versus girls and across puberty. Mean/median height z-scores remained constant for all four patient groups. In contrast, mean/median weight z-scores increased with aging, including after height-adjustment, resembling the recent trend for American children. However, excessive weight gain was typically not observed and mean/median values became average for height. Mean/median z-scores calculated routinely for chronologic age did not change for grip strength or for lumbar spine or total hip BMD. However, height-correction of the cohort suggested some worsening of grip strength z-scores and indicated improvement in spine BMD z-scores. Overall, in affected children and adolescents, HPP represents a clinically stable but chronic disorder.

Prevention of Lethal Murine Hypophosphatasia by Neonatal Ex Vivo Gene Therapy Using Lentivirally Transduced Bone Marrow Cells.

Hypophosphatasia (HPP) is an inherited skeletal and dental disease caused by loss-of-function mutations in the gene that encodes tissue-nonspecific alkaline phosphatase (TNALP). The major symptoms of severe forms of the disease are bone defects, respiratory insufficiency, and epileptic seizures. In 2015, enzyme replacement therapy (ERT) using recombinant bone-targeted TNALP with deca-aspartate (D10) motif was approved to treat pediatric HPP patients in Japan, Canada, and Europe. However, the ERT requires repeated subcutaneous administration of the enzyme because of the short half-life in serum. In the present study, we evaluated the feasibility of neonatal ex vivo gene therapy in TNALP knockout (Akp2(-/-)) HPP mice using lentivirally transduced bone marrow cells (BMC) expressing bone-targeted TNALP in which a D10 sequence was linked to the C-terminus of soluble TNALP (TNALP-D10). The Akp2(-/-) mice usually die within 20 days because of growth failure, epileptic seizures, and hypomineralization. However, an intravenous transplantation of BMC expressing TNALP-D10 (ALP-BMC) into neonatal Akp2(-/-) mice prolonged survival of the mice with improved bone mineralization compared with untransduced BMC-transplanted Akp2(-/-) mice. The treated Akp2(-/-) mice were normal in appearance and experienced no seizures during the experimental period. The lentivirally transduced BMC were efficiently engrafted in the recipient mice and supplied TNALP-D10 continuously at a therapeutic level for at least 3 months. Moreover, TNALP-D10 overexpression did not affect multilineage reconstitution in the recipient mice. The plasma ALP activity was sustained at high levels in the treated mice, and tissue ALP activity was selectively detected on bone surfaces, not in the kidneys or other organs. No ectopic calcification was observed in the ALP-BMC-treated mice. These results indicate that lentivirally transduced BMC can serve as a reservoir for stem cell-based ERT to rescue the Akp2(-/-) phenotype. Neonatal ex vivo gene therapy thus appears to be a possible treatment option for treating severe HPP.

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

UNLABELLED: 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. OBJECTIVES: Because 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. METHODS: Cranial 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. RESULTS: Alpl(-/-) 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. CONCLUSIONS: These 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.

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.

Clinical spectrum of hypophosphatasia diagnosed in adults.

The presentation of hypophosphatasia (HPP) diagnosed in adults demonstrates a wide range of clinical manifestations, many of which are nonspecific. We sought to assess clinical characteristics of adult HPP by evaluation of Mayo Clinic Rochester adults diagnosed with HPP from 1976 through 2008. Subjects were identified by diagnostic code or medical records. Inclusion criteria were age ≥18 years at diagnosis; low serum alkaline phosphatase (AP) without bisphosphonate therapy; and one additional element: elevated pyridoxal 5'-phosphate (PLP) or urine phosphoethanolamine (PEA), evidence of osteomalacia, or family history. We were unable to distinguish manifesting carriers from silent unaffected carriers due to lack of a prospective standardized clinical evaluation and the absence of genetic testing. HPP was diagnosed in 22 unrelated adults (median age 49 years; 68% women). Most patients (68%) were symptomatic at presentation with features including musculoskeletal pain (41%) or incident fracture (18%). A history of fracture was present in 54%: hip/femoral neck (23%), feet (23%, all women), wrist (18%), and spine (9%, all men). Nine patients (36%) had multiple fractures while 4 (all women) had subtrochanteric femur fractures. Radiographic chondrocalcinosis (27%) and documented pyrophosphate arthropathy (14%) were only observed in women. Median minimum serum AP was 43% below the lower normal limit. Urine PEA was elevated in 15/16 patients (94%). PLP median was 68 µg/L (normal, 5-50 µg/L) and all (n=8) were above normal. Symptomatic subjects had more fractures and chondrocalcinosis, lower median minimum AP and PLP and higher median PEA levels. Clinical features more common in fracture patients included symptoms at presentation, history of childhood rickets, dental abnormalities, lower median minimum AP and PLP, and higher median urine PEA. Four subjects had iliac crest bone biopsies, with 2/4 specimens consistent with osteomalacia. These results suggest that adult HPP demonstrates a wide spectrum of clinical manifestations including musculoskeletal pain, fractures, chondrocalcinosis and dental anomalies with some overlap in laboratory characteristics in relationship to disease severity. In addition to genetic and environmental factors, gender may influence the clinical expression of HPP.

Tooth root dentin mineralization defects in a mouse model of hypophosphatasia.

Tissue-nonspecific alkaline phosphatase (TNAP) is expressed in mineralizing tissues and functions to reduce pyrophosphate (PP(i) ), a potent inhibitor of mineralization. Loss of TNAP function causes hypophosphatasia (HPP), a heritable disorder marked by increased PP(i) , resulting in rickets and osteomalacia. Tooth root cementum defects are well described in both HPP patients and in Alpl(-/-) mice, a model for infantile HPP. In Alpl(-/-) mice, dentin mineralization is specifically delayed in the root; however, reports from human HPP patients are variable and inconsistent regarding dentin defects. In the current study, we aimed to define the molecular basis for changes in dentinogenesis observed in Alpl(-/-) mice. TNAP was found to be highly expressed by mature odontoblasts, and Alpl(-/-) molar and incisor roots featured defective dentin mineralization, ranging from a mild delay to severely disturbed root dentinogenesis. Lack of mantle dentin mineralization was associated with disordered and dysmorphic odontoblasts having disrupted expression of marker genes osteocalcin and dentin sialophosphoprotein. The formation of, initiation of mineralization within, and rupture of matrix vesicles in Alpl(-/-) dentin matrix was not affected. Osteopontin (OPN), an inhibitor of mineralization that contributes to the skeletal pathology in Alpl(-/-) mice, was present in the generally unmineralized Alpl(-/-) mantle dentin at ruptured mineralizing matrix vesicles, as detected by immunohistochemistry and by immunogold labeling. However, ablating the OPN-encoding Spp1 gene in Alpl(-/-) mice was insufficient to rescue the dentin mineralization defect. Administration of bioengineered mineral-targeting human TNAP (ENB-0040) to Alpl(-/-) mice corrected defective dentin mineralization in the molar roots. These studies reveal that TNAP participates in root dentin formation and confirm that reduction of PP(i) during dentinogenesis is necessary for odontoblast differentiation, dentin matrix secretion, and mineralization. Furthermore, these results elucidate developmental mechanisms underlying dentin pathology in HPP patients, and begin to explain the reported variability in the dentin/pulp complex pathology in these patients.

Skeletal mineralization defects in adult hypophosphatasia--a clinical and histological analysis.

UNLABELLED: Histomorphometry and quantitative backscattered electron microscopy of iliac crest biopsies from patients with adult hypophosphatasia not only confirmed the expected enrichment of non-mineralized osteoid, but also demonstrated an altered trabecular microarchitecture, an increased number of osteoblasts, and an impaired calcium distribution within the mineralized bone matrix. INTRODUCTION: Adult hypophosphatasia is an inherited disorder of bone metabolism caused by inactivating mutations of the ALPL gene, encoding tissue non-specific alkaline phosphatase. While it is commonly accepted that the increased fracture risk of the patients is the consequence of osteomalacia, there are only few studies describing a complete histomorphometric analysis of bone biopsies from affected individuals. Therefore, we analyzed iliac crest biopsies from eight patients and set them in direct comparison to biopsies from healthy donors or from individuals with other types of osteomalacia. METHODS: Histomorphometric analysis was performed on non-decalcified sections stained either after von Kossa/van Gieson or with toluidine blue. Bone mineral density distribution was quantified by backscattered electron microscopy. RESULTS: Besides the well-documented enrichment of non-mineralized bone matrix in individuals suffering from adult hypophosphatasia, our histomorphometric analysis revealed alterations of the trabecular microarchitecture and an increased number of osteoblasts compared to healthy controls or to individuals with other types of osteomalacia. Moreover, the analysis of the mineralized bone matrix revealed significantly decreased calcium content in patients with adult hypophosphatasia. CONCLUSIONS: Taken together, our data show that adult hypophosphatasia does not solely result in an enrichment of osteoid, but also in a considerable degradation of bone quality, which might contribute to the increased fracture risk of the affected individuals.

Whole-body MRI in the childhood form of hypophosphatasia.

Hypophosphatasia (HPP) is a rare inborn error of bone metabolism caused by various defects in the gene coding for the tissue-nonspecific alkaline phosphatase (TNSAP). It results in a reduced activity of the TNSAP and elevated concentrations of its substrates, including inorganic pyrophosphate. Clinical features of HPP include defective bone mineralisation with bone deformities, fractures and chronic non-bacterial osteomyelitis. Renal damage due to calcification, craniosynostosis and dental abnormalities with premature loss of dentition are further complications. Until now, detailed descriptions of whole-body magnetic resonance imaging (WB-MRI) in HPP do not exist. Here, we analysed WB-MRIs of 4 children with the childhood form of HPP. Deformities and defects of the long bones could be seen. All patients showed radiological lesions in the metaphyses of the long bones predominantly in the lower extremities being consistent with hyperaemia and oedema. Differential diagnosis includes an inflammatory process being active in these locations.

Lack of sustained response to teriparatide in a patient with adult hypophosphatasia.

INTRODUCTION: Hypophosphatasia (HPP) is a rare genetic disorder characterized by low serum alkaline phosphatase (ALP) and defective bone mineralization predisposing to poorly healing pseudofractures and fractures. Experience with teriparatide in HPP is limited. METHODS: A 53-yr-old woman was diagnosed with HPP on the basis of repeatedly low serum ALP (6-8 IU/liter; normal, 30-120 IU/liter), high urine phosphoethanolamine (PEA) and serum pyridoxal 5'-phosphate (PLP) concentrations, and pseudofractures on the lateral aspect of both proximal femurs. Teriparatide (20 microg/d sc) was initiated 4 months after surgery for a painful nonhealing left femoral fracture sustained after minimal trauma. RESULTS: The patient carried two missense mutations at exons 6 and 11 (Ala176Thr and Val423Ala) and one polymorphism at exon 12 (Val522Ala) of the tissue nonspecific ALP gene (TNSALP). Pain resolved and mobility improved with teriparatide treatment. Serum ALP doubled, and both urine PEA and serum PLP decreased. Markers of bone remodeling increased markedly. Comparison of bone biopsy before and 5 months after teriparatide revealed increased amounts of osteoid and osteoblast numbers. After 8 months, there was complete healing of the pseudofracture of the right femur, and bony callus was apparent on the left. Despite good compliance, serum ALP and PLP and urine PEA returned to baseline with between 8 and 13 months of treatment. CONCLUSION: This is the first bone biopsy report of teriparatide response in adult HPP. In contrast to the two previously reported cases, biochemical response to teriparatide was unsustained, suggesting that response may be variable depending on the TNSALP gene mutation.

Case report: multiple fractures in a patient with mutations of TWIST1 and TNSALP.

Hypophosphatasia is a rare inherited disorder characterized by defective skeletal mineralization and low alkaline phosphatase activities in the serum. The genetic cause of hypophosphatasia is believed related to inactivating mutations in the TNSALP gene, encoding tissue-nonspecific alkaline phosphatase. Another rare inheritable disease, Saethre-Chotzen syndrome, leads to premature fusion of the cranial sutures caused by heterozygous mutations of the human TWIST1 gene. Because the two disorders apparently are not genetically related (only reported individually) yet both involve defective skeletal formation, we believe it is important to report our findings on a patient harboring mutations of TNSALP and TWIST1.

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.

Enhancement of drug delivery to bone: characterization of human tissue-nonspecific alkaline phosphatase tagged with an acidic oligopeptide.

Hypophosphatasia is caused by deficiency of activity of the tissue-nonspecific alkaline phosphatase (TNSALP), resulting in a defect of bone mineralization. Enzyme replacement therapy (ERT) with partially purified plasma enzyme was attempted but with little clinical improvement. Attaining clinical effectiveness with ERT for hypophosphatasia may require delivering functional TNSALP enzyme to bone. We tagged the C-terminal-anchorless TNSALP enzyme with an acidic oligopeptide (a six or eight residue stretch of L-Asp), and compared the biochemical properties of the purified tagged and untagged enzymes derived from Chinese hamster ovary cell lines. The specific activities of the purified enzymes tagged with the acidic oligopeptide were the same as the untagged enzyme. In vitro affinity experiments showed the tagged enzymes had 30-fold higher affinity for hydroxyapatite than the untagged enzyme. Lectin affinity chromatography for carbohydrate structure showed little difference among the three enzymes. Biodistribution pattern from single infusion of the fluorescence-labeled enzymes into mice showed delayed clearance from the plasma up to 18 h post infusion and the amount of tagged enzyme retained in bone was 4-fold greater than that of the untagged enzyme. In vitro mineralization assays with the bone marrow from a hypophosphatasia patient using each of the three enzymes in the presence of high concentrations of pyrophosphate provided evidence of bone mineralization. These results show the anchorless enzymes tagged with an acidic oligopeptide are delivered efficiently to bone and function bioactively in bone mineralization, at least in vitro. They suggest potential advantages for use of these tagged enzymes in ERT for hypophosphatasia, which should be explored.

Matrix vesicles in osteomalacic hypophosphatasia bone contain apatite-like mineral crystals.

Hypophosphatasia, a heritable disease characterized by deficient activity of the tissue nonspecific isoenzyme of alkaline phosphatase (TNSALP), results in rickets and osteomalacia. Although identification of TNSALP gene defects in hypophosphatasia establishes a role of ALP in skeletal mineralization, the precise function remains unclear. The initial site of mineralization (primary mineralization) normally occurs within the lumen of TNSALP-rich matrix vesicles (MVs) of growth cartilage, bone, and dentin. We investigated whether defective calcification in hypophosphatasia is due to a paucity and/or a functional failure of MVs secondary to TNSALP deficiency. Nondecalcified autopsy bone and growth plate cartilage from five patients with perinatal (lethal) hypophosphatasia were studied by nondecalcified light and electron microscopy to assess MV numbers, size, shape, and ultrastructure and whether hypophosphatasia MVs contain apatite-like mineral, as would be the case if these MVs retained their ability to concentrate calcium and phosphate internally despite a paucity of TNSALP in their investing membranes. We found that hypophosphatasia MVs are present in approximately normal numbers and distribution and that they are capable of initiating internal mineralization. There is retarded extravesicular crystal propagation. Thus, in hypophosphatasia the failure of bones to calcify appears to involve a block of the vectorial spread of mineral from initial nuclei within MVs, outwards, into the matrix. We conclude that hypophosphatasia MVs can concentrate calcium and phosphate internally despite a deficiency of TNSALP activity.