A Reference Range for Plasma Levels of Inorganic Pyrophosphate in Children Using the ATP Sulfurylase Method.

PURPOSE: Generalized arterial calcification of infancy, pseudoxanthoma elasticum, autosomal recessive hypophosphatemic rickets type 2, and hypophosphatasia are rare inherited disorders associated with altered plasma levels of inorganic pyrophosphate (PPi). In this study, we aimed to establish a reference range for plasma PPi in the pediatric population, which would be essential to support its use as a biomarker in children with mineralization disorders. METHODS: Plasma samples were collected from 200 children aged 1 day to 18 years who underwent blood testing for medical conditions not affecting plasma PPi levels. PPi was measured in proband plasma utilizing a validated adenosine triphosphate (ATP) sulfurylase method. RESULTS: The analytical sensitivity of the ATP sulfurylase assay consisted of 0.15 to 10 µM PPi. Inter- and intra-assay coefficients of variability on identical samples were below 10%. The standard range of PPi in the blood plasma of children and adolescents aged 0 to 18 years was calculated as 2.36 to 4.44 µM, with a median of 3.17 µM, with no difference between male and female probands. PPi plasma levels did not differ significantly in different pediatric age groups. MAIN CONCLUSIONS: Our results yielded no noteworthy discrepancy to the reported standard range of plasma PPi in adults (2-5 µM). We propose the described ATP sulfurylase method as a diagnostic tool to measure PPi levels in plasma as a biomarker in the pediatric population.

Cross-sectional analysis: clinical presentation of children with persistently low ALP levels.

OBJECTIVES: Low activity of serum alkaline phosphatase (ALP) is a hallmark of hypophosphatasia (HPP), but low readings of ALP are not always recognized in clinical routine. Understanding the clinical presentations associated with low ALP may contribute to a timelier diagnosis of HPP. METHODS: Data from paediatric patients with low ALP, excluding patients in intensive care and with oncological/haematological disorders, were analysed. Most recent ALP values, previous diagnoses, medication and relevant symptoms were extracted from patient records at nine specialised centres and analysed descriptively. A relationship between body height and ALP values was scrutinised by linear regression. RESULTS: Of 370 children, 15 (4.1%) had a diagnosis of HPP. In the subgroup without a diagnosis of HPP, 241 (67.9%) out of 355 patients had one or more medical conditions known to be associated with low serum ALP. Of those, hypothyroidism, malnutrition and steroid administration were most frequent. Characteristic symptoms, particularly, short stature, muscle weakness and delay of motor development were more frequent and ALP values were lower in patients with documented HPP diagnosis compared to patients without diagnosis of HPP (Ø z-scores: -2.52) (interquartile range [IQR] = 0.20) vs. -1.96 (IQR = 0.87). A weak positive linear relationship between z-scores of ALP and body height was identified (p<0.001). CONCLUSIONS: This analysis of paediatric patient records elucidates a wide range of disorders associated with low ALP activity. In case of additional specific symptoms, HPP should always be considered as a differential diagnosis.

Tissue non-specific alkaline phosphatase activity and mineralization capacity of bi-allelic mutations from severe perinatal and asymptomatic hypophosphatasia phenotypes: Results from an in vitro mutagenesis model.

BACKGROUND: Hypophosphatasia (HPP) is an inherited metabolic bone disease characterized by reduced mineralization due to mutations in the tissue non-specific alkaline phosphatase (ALPL) gene. HPP is clinically variable with extensive allelic heterogeneity in the ALPL gene. We report the findings of in vitro functional studies following site-directed mutagenesis in bi-allelic mutations causing extreme clinical phenotypes; severe perinatal and asymptomatic HPP. AIMS: Elucidate genotype-phenotype correlation using in vitro functional studies and 3 dimensional (3D) ALP modelling. METHODS: Clinical, biochemical and radiological features were recorded in two children with extreme HPP phenotypes: Subject 1 (S1): Perinatal HPP with compound heterozygous mutations (c.110T>C; c.532T>C); Subject 2 (S2): asymptomatic with homozygous missense mutation (c.715G>T). Plasmids created for mutants 1 c.110T>C (L37P), 2 c.532T>C (Y178H) and 3 c.715G>T (D239Y) using in vitro mutagenesis were transfected into human osteosarcoma (U2OS) cells and compared to wildtype (WT) and mock cDNA. ALP activity was measured using enzyme kinetics with p-nitrophenylphosphate. Mineral deposition was evaluated photometrically with Alizarin Red S staining after culture with mineralization medium. Western blot analysis was performed to identify the mature type protein expression (80 kDa). Mutations were located on a 3D ALP model. Co-transfection was performed to identify dominant negative effect of the mutants. RESULTS: Phenotype: S1, had typical perinatal HPP phenotype at birth; extremely under-mineralized bones and pulmonary hypoplasia. S2, diagnosed incidentally by laboratory tests at 4 years, had normal growth, development, dentition and radiology. All S2's siblings (3 homozygous, 1 heterozygous) were asymptomatic. All subjects had typical biochemical features of HPP (low ALP, high serum pyridoxal-5'-phosphate), except the heterozygous sibling (normal ALP). Functional assay: Mutants 1 and 2 demonstrated negligible ALP activity and mineralization was 7.9% and 9.3% of WT, respectively. Mutant 3 demonstrated about 50% ALP activity and 15.5% mineralization of WT. On Western blot analysis, mutants 1 and 2 were detected as faint bands indicating reduced expression and mutant 3 was expressed as mature form protein with 50% of WT expression. Mutant 1 was located near the Glycosylphosphatidylinositol anchor, 2 at the core structure of the ALP protein and 3 at the periphery of the protein structure. Co-transfection did not reveal a dominant negative effect in any of the mutants. CONCLUSION: Our findings expand the current knowledge of functional effect of individual mutations and the importance of their location in the ALP structure.

Neurological symptoms in Hypophosphatasia.

Hypophosphatasia (HPP) typically manifests with fractures, tooth loss, and muscle pain. Although mental health diagnoses and neurological symptoms have not been previously well documented in HPP, they occur commonly. The recognition of non-traditional symptoms may improve patient satisfaction, preempt costly evaluation and misdiagnosis, and lead to further treatment options. INTRODUCTION: Hypophosphatasia (HPP) is an inborn error of metabolism due to deficiency of tissue non-specific alkaline phosphatase (TNSALP). It is traditionally characterized by rickets in children and osteomalacia in adults, along with fractures, tooth loss, and muscle pain. Neurological symptoms and mental health diagnoses have not been widely reported, and we therefore report their prevalence in a cohort of patients with HPP. METHODS: A retrospective chart review was performed on a series of 82 HPP patients. Patient charts were reviewed to identify the possible presence and onset of 13 common neurological symptoms. RESULTS: Median age was 36 years (2 to 79). Seventeen had adult onset HPP (> 18 years) and 65 had pediatric onset HPP (< 18 years). Median time from symptom onset to HPP diagnosis was 8 years (0 to 67). Seventy-four percent had a family history of bone disease, while 17% had a family history of neurologic disease. Bone problems occurred in 89%, dental problems in 77%, and muscle problems in 66%. Fatigue occurred in 66%, headache in 61%, sleep disturbance in 51%, gait change in 44%, vertigo in 43%, depression in 39%, anxiety in 35%, neuropathy in 35%, and hearing loss in 33%. CONCLUSIONS: The extra-skeletal manifestations of HPP, specifically neurological symptoms, have not been previously well documented. However, mental health diagnoses and neurological symptoms such as headache and sleep disturbance occur commonly in patients with HPP. The recognition of non-traditional symptoms in HPP may improve patient satisfaction, preempt costly evaluation and misdiagnosis, and may lead to further treatment options.

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)

A controlled study of the effects of ferric carboxymaltose on bone and haematinic biomarkers in chronic kidney disease and pregnancy.

Background: Intravenous (IV) iron can modulate fibroblast growth factor 23 (FGF23) concentrations and cause transient but significant hypophosphataemia. However, it is unknown what other markers might be involved, especially in different patient groups. This study aimed to determine changes in bone and haematinic biomarkers following IV ferric carboxymaltose (FCM) and to identify risk factors for hypophosphataemia in pregnant subjects and those with chronic kidney disease (CKD). Methods: Changes in bone [serum FGF23, fractional excretion of phosphate urinary fractional excretion of phosphate (FEPi), serum phosphate and serum vitamin D derivatives] and haematinic [plasma hepcidin, serum ferritin and transferrin saturation (TSAT)] biomarkers after 1 g of IV FCM were followed in iron-deficient pregnant and CKD patients and compared with controls (estimated glomerular filtration rate > 60 mL/min/1.73 m2). Data were collected at baseline and up to 42 days after infusion. Risk factors for post-FCM hypophosphataemia were also assessed. Results: Sixty-five subjects completed the study (control, n = 20; pregnant, n = 20; CKD, n = 25). A uniform but variable increase across groups was seen in intact FGF23 (peak Day 2), whereas c-terminal FGF23 varied markedly. Trough serum phosphate timed with the peak FEPi at Day 7, recovering by Day 21 in the pregnant group and Day 42 in other groups. Independent predictors of a low phosphate nadir included baseline phosphate, FEPi and weight-adjusted FCM dose. All groups showed an early and marked increase in plasma hepcidin (peak Day 2), serum ferritin and TSAT (peak Day 7 for both). Conclusions: Changes in bone and haematinic biomarkers differ between patient groups following IV FCM. For patients with lower serum phosphate concentrations, limiting the dose and measuring levels 7 days after administration may mitigate clinically significant hypophosphataemia.

Parental serum alkaline phosphatase activity as an auxiliary tool for prenatal diagnosis of hypophosphatasia.

OBJECTIVE: The objective of this study is to clarify the usefulness of parental alkaline phosphatase (ALP) for prenatal diagnosis of hypophosphatasia (HPP). METHODS: Maternal (m) and paternal (p) ALP values were measured in 77 cases from a multicenter cohort (fetal skeletal dysplasia forum in Japan) of cases with short limbs on ultrasonography during pregnancy. After birth, X-rays, cord blood ALP, and gene analysis were evaluated to achieve an exact diagnosis. The screening usefulness of ALP was examined retrospectively. RESULTS: Seventeen cases were eventually diagnosed as HPP and 60 as not HPP; the overall mean m-ALP and p-ALP (standard deviation) values were 133.4 (53) versus 197 (69) IU/L and 149.6 (71.8) versus 231 (61.4) IU/L (p < 0.001). Receiver operating characteristic curve analysis showed that the optimal m-ALP and p-ALP cutoff values were 123 and 165 IU/L, respectively. Presence of at least one of the m-ALP or p-ALP values abnormally low had a sensitivity, specificity, and positive predictive values of 82% (14/17), 93%, and 78%, respectively, for the diagnosis of HPP. CONCLUSION: Parental ALP measurement might be an auxiliary tool to hone in the prenatal diagnosis of fetal HPP. © 2017 John Wiley & Sons, Ltd.

Hypophosphatasia: oral cavity and dental disorders.

Dental anomalies exist in every subtype of hypophosphatasia (HPP), from the most severe to the most moderate, called odontohypophosphatasia. The forms are defined by the age at onset of the initial symptoms. These anomalies affect all dental mineralized tissues from enamel, dentin and cementum to alveolar bone in a gradient proportional to the severity of the disease. Early loss of the deciduous teeth, before 3 years of age, and then possibly of the permanent teeth, is due to an abnormality of the cementum, the tissue attaching the teeth to alveolar bone, and is the most frequent abnormality. Tooth loss is a very important diagnostic sign and needs to be recognized. Patients with HPP need specialized oral and dental care in coordination with the reference and expert centers. The oral and dental signs and their treatment remain poorly known. The recording of the abnormalities and their treatment in a registry is indispensable in order to enhance patient management and oral and dental health.

Osteomalacia with low alkaline phosphatase: a not so rare condition with important consequences.

Hypophosphatasia is a genetic disorder, characterised by a dysfunctional tissue-non-specific isoenzyme of alkaline phosphatase that impacts bone metabolism and predisposes to osteomalacia or rickets. The clinical presentation is very diverse, depending on the age of onset and the severity of the disease. Several forms of hypophosphatasia are recognised. We present a case of a 50-year-old woman with low impact fractures and loss of teeth at a young age. She also had a low alkaline phosphatase and was diagnosed with adult hypophosphatasia. Although the severe forms of hypophosphatasia are rather rare, the adult form is thought to occur quite frequently. As this condition is not well known by healthcare professionals, the time to diagnosis and initiation of adequate treatment is often postponed. When encountering a patient with low alkaline phosphatase, low bone density or a history of bone fractures, the possibility of hypophosphatasia should be considered.

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.

Treatment of adult hypophosphatasia with teriparatide.

OBJECTIVE: To describe the effects of 24 months of teriparatide therapy in an adult with hypophosphatasia, which thus far has no established medical treatment. METHODS: A 75-year-old woman with hypophosphatasia was treated with ergocalciferol and calcium supplements for 2 years. She had sustained multiple spontaneous and low-trauma fractures since she was 10 years old. Baseline biochemical values (and reference ranges) were as follows: serum total alkaline phosphatase ranged from 14 to 17 U/L (30 to 110), bone-specific alkaline phosphatase (BSALP) was 5 U/L (14 to 43), serum phosphorus was elevated at 5.4 mg/dL (2.6 to 4.4), and pyridoxal 5'-phosphate was high at 250 ng/mL (5 to 30). At baseline, she had mild secondary hyperparathyroidism (intact parathyroid hormone, 76 pg/mL; reference range, 10 to 65), which was corrected by the calcium supplementation and vitamin D therapy. Dual-energy x-ray absorptiometry (DXA) scanning in 2003 showed L1-L4 bone mineral density (BMD) of 0.786 g/cm2, T score of -3.3, and Z score of -1.7; DXA also showed femoral neck BMD of 0.740 g/cm2, T score of -2.5, and Z score of -0.5. During walking, the patient sustained a low-trauma fracture in a metatarsal. Teriparatide, synthetic parathyroid hormone(1-34), in a dosage of 20 microg subcutaneously was given daily from April 2004 until June 2006. RESULTS: After about 1.5 years of teriparatide therapy, BSALP reached the lower end of the reference range at 16 U/L, and after 24 months of continuous teriparatide treatment, both serum total alkaline phosphatase and BSALP normalized at 30 U/L and 18 U/L, respectively. Pyridoxal 5'-phosphate declined from a baseline of 250 to 188 ng/mL after 17 months of treatment. Urinary N-telopeptide increased from a baseline of <6 to 19 after 17 months and to 70 bone collagen equivalents/mmol creatinine after 24 months of anabolic therapy. Repeated DXA scanning showed a substantial improvement in lumbar spine BMD and stability in hip BMD. The patient experienced no clinical fractures or adverse events during teriparatide therapy. CONCLUSION: In one woman with adult hypophosphatasia, 2 years of teriparatide treatment improved biochemical markers of bone remodeling and increased skeletal mineralization. Teriparatide may prove to be a viable treatment for adult hypophosphatasia; thus, this intervention warrants further evaluation.

[Hyperphosphatasia and hypophosphatasia in childhood]. / Hyperphosphatasie und Hypophosphatasie im Kindesalter.

The treatment of phosphate diabetes and hyperphosphatasia requires an interdisciplinary therapy concept between paediatricians and orthopaedic surgeons. The surgical challenge is the correction of the multiplanar bending deformities and the pathological fractures. Different techniques are discussed in the literature without an outstanding recommendation for a special approach. This contribution gives an overview of the published methods and discusses various surgical concepts in view of our own clinical experience.

Hypophosphatasia.

Hypophosphatasia is a rare inherited metabolic disease characterised by reduced plasma and tissue alkaline phosphatase activity, and may present in infancy, childhood or adulthood. The differing modes of inheritance, presentation and natural history are likely to reflect variable expression of the alkaline phosphatase gene defect. A case of infantile hypophophatasia presenting with hypercalcaemia is described and the histological and radiological resolution of the mineralisation defect present initially are reported.

Reduced bone mineral density and low parathyroid hormone levels in patients with the adult form of hypophosphatasia.

Hypophosphatasia is a heritable metabolic bone disease with characteristically reduced levels of alkaline phosphatase (ALP) in the blood, liver, kidney and bone. ALP levels are normal in the intestine and placenta. About 300 patients have been reported so far in the literature. Three kindreds with 52 known subjects are described here, whereby 12 subjects could be examined osteologically. Four subjects were patients and had clinical signs of the disease: spontaneous fractures of the metatarsals or femora and low ALP serum levels ranging between 8 and 23 U/l (normal range 40-170 U/l). Four other members without fractures had reduced ALP levels; they might be carriers of the disease and develop symptoms later in life. The four remaining subjects had normal ALP levels and no signs of the disease. Serum levels of intact parathyroid hormone (iPTH) were found to be in the lower normal range and serum calcium levels in the upper normal range. There was a significant (P less than 0.05) negative correlation between iPTH and serum calcium levels (r = -0.78). Urinary calcium excretion was increased in 3 subjects with fractures. 25-OH-D3 levels were increased in 6 of 8 subjects without any treatment. The bone mineral density (BMD) was measured using dual X-ray absorptiometry of the lumbar spine, representing mainly trabecular bone, and single-photon absorptiometry of the forearm, measuring mainly cortical bone. Z-scores of the spinal bone mass ranged between 0.38 and -1.95 SD; Z-scores of the forearm bone mass ranged between 0.53 and -2.47 SD with the lowest values in patients with fractures.(ABSTRACT TRUNCATED AT 250 WORDS)

Clinical significance of a low serum alkaline phosphatase.

The reasons for a low serum alkaline phosphatase activity were reviewed in a 1-yr retrospective study of all the results emanating from a central, university hospital laboratory. Apart from occasional errors, hypophosphatasaemia was encountered in neonates undergoing exchange transfusions with plasma, in patients (particularly children) receiving chemotherapy and during cardio-pulmonary bypass. Low activity values were recorded in several individuals in the absence of any obvious cause. This would suggest that the definition of the lower limit of the reference range for alkaline phosphatase is arbitrary, thus limiting the use of low serum activity as a marker of disease.

Circulating vitamin D metabolite levels in hypophosphatasia.

25OHD, 1,25,-(OH))2D, and 24,25-(OH)2D were assayed in the serum of 16 patients with the infantile, childhood, or adult form of hypophosphatasia. Except for diminished 1,25-(OH)2D and elevated 24,25-(OH)2D levels in 2 infants (which could be attributed to nonparathyroid hormone-mediated hypercalcemia), the mean circulating level of each vitamin D metabolite was normal in the 3 patient groups. Abnormalities in vitamin D metabolism do not appear to contribute to the pathogenesis of this rare hereditary form of rickets or osteomalacia, which occurs despite normal circulating calcium, inorganic phosphate, and vitamin D metabolite levels.

Vitamin D metabolism in hypophosphatasia.

A 4-month-old boy with the infantile form of hypophosphatasia was followed for 9 months with measurements of serum calcium, phosphate, alkaline phosphatase and various vitamin D metabolites, together with urinary excretion of cyclic AMP. During the initial hypercalcemic stage the serum concentration of 25-hydroxyvitamin D was normal. Urinary cyclic AMP was low and the serum concentration of the dihydroxymetabolites of vitamin D were appropriate to the high serum calcium with low 1,25-(OH)2D and relatively high 24,25(OH)2D and 25,26(OH)2D levels. Due to restrictions of the vitamin D intake and lack of exposure to sun he developed vitamin D-deficiency rickets at 9 months of age with very low serum concentration of 25-hydroxyvitamin D and markedly increased urinary excretion of cyclic AMP. Following vitamin D treatment the serum level of 1,25(OH)2D showed a brisk rise to a considerably elevated value. Initially the serum concentration of alkaline phosphatase was well below the normal range, rose markedly during the stage of active rickets and returned to the characteristic low levels of hypophosphatasia with healing of the rickets.