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.

Hipofosfatasemia crónica persistente de causa no determinada y su repercusión músculo-esquelética / Persistent hypophosphatasemia and its musculoskeletal repercussion

La fosfatasa alcalina baja o hipofosfatasemia, ya sea debida a causas genéticas (hipofosfatasia) o secundarias, presenta correlato clínico. Nuestro objetivo es estimar la prevalencia de hipofosfatasemia crónica persistente y describir sus hallazgos osteometabólicos. Se realizó una búsqueda electrónica de afiliados adultos al Hospital Italiano de Buenos Aires, entre 2013 y 2017, con al menos 2 determinaciones de fosfatasa alcalina igual a 30 UI/l o menor y ninguna mayor de 30 UI/l (rango de referencia 30-100 UI/l). Se excluyeron aquellos con causas secundarias diagnosticadas y se analizaron los correlatos clínico y bioquímico. Se detectó hipofosfatasemia crónica persistente en 78 de 105.925, 0,07% (0,06-0,09) de los afiliados. Solo uno fue excluido por tener causa secundaria. Eran 61,1% mujeres de 44 (34-56) años, fosfatasa alcalina 24 (20-27) UI/L, fosfatemia 4,1 (3,8-4,6) mg/dl. Se observaron osteoartritis, calcificaciones vasculares y fracturas, menos frecuentemente litiasis renal, calcificación del ligamento longitudinal común anterior, pérdida dental y convulsiones. El 63,6% tenían al menos una de las características clínico-radiológicas evaluadas, pero en solo 5,2% fue mencionado el diagnóstico de hipofosfatasemia en la historia clínica. La densitometría evidenció algún grado de afección (osteopenia u osteoporosis) en 76,2%. Se constataron 19 fracturas, con predominio en radio. La prevalencia de hipofosfatasemia fue similar a lo previamente reportado. El reconocimiento fue bajo; sin embargo, se observaron variadas manifestaciones músculo-esqueléticas, similares a las descriptas en la hipofosfatasia del adulto, por lo cual ­ante una hipofosfatasemia sin causa secundaria­ se sugiere considerar este diagnóstico. (AU)

Low alkaline phosphatase (ALP) or hypophosphatasemia either due to genetic (hypophosphatasia) or secondary causes, presents a clinical correlate. Our objectives are to estimate the prevalence of persistent hypophosphatasemia and to describe the clinical findings. We performed a search using the electronic medical records of the members of the Hospital Italiano de Buenos Aires health care system, between 2013 and 2017. Adult members with ≥ 2 ALP ≤ 30 IU/l, no ALP >30 IU/l (normal range 30-100 UI/l) and without diagnosed secondary causes were analyzed. Persistent hypophosphatasemia was detected in 78 of 105.925, 0.07% (0.06-0.09) of members. Only one was excluded due to a secondary cause, 61.1% were women, 44 (34-56) year-old, ALP 24 (20-27) IU/l and phosphatemia 4.1 (3.8-4.6) mg/dl. Osteoarthritis, vascular calcifications and fractures were detected, and nephrolithiasis, DISH (Diffuse idiopathic skeletal hyperostosis), tooth loss, and seizures were less frequently observed. At least one of the mentioned characteristics were present in 63.6 %, but only 5.2% had hypophosphatasemia registered in their clinical record. Densitometry showed osteopenia or osteoporosis in 76.2%. There were 19 fractures, most of them in radius. The prevalence of hypophosphatasemia was similar to what has been previously reported. Hypophosphatasemia finding in medical records was low, but far from being asymptomatic, clinical manifestations were observed. In the presence of hypophosphatasemia without a secondary cause, adult hypophosphatasia should be uspected. (AU)

Interference of Asfotase Alfa in Immunoassays Employing Alkaline Phosphatase Technology.

BACKGROUND: Asfotase alfa (STRENSIQ®, Alexion Pharmaceuticals, Inc.) is the only approved treatment for patients with pediatric-onset hypophosphatasia, a disease caused by a mutation in the tissue-nonspecific alkaline phosphatase (TNSALP) gene. ALP is often used as signaling system in routine immunoassays. Because asfotase alfa contains the active site of the full ALP enzyme, it can catalyze the substrate as the antibody-conjugated ALP would within an assay. Therefore, its presence in a treated patient's sample may generate false positive or false negative results. We investigated whether the presence of asfotase alfa within a sample induced interference in immunoassays that utilize ALP or alternative detection systems. METHODS: Asfotase alfa was added to samples at concentrations from 0.08-5 µg/mL and analysed on various immunoassays following manufacturer's instructions. RESULTS: Asfotase alfa was detected in all ALP assays but ALKP1 (RayBiotech). We observed no changes in normetanephrine and noradrenaline (IBL) at any asfotase alfa concentration. However, asfotase alfa notably interfered in an oxytocin (ENZO) assay in nonextracted samples. Extraction using a C18 column eliminated the interference. No interference was observed on automated analyzers using alternative detection system (COBAS fT4 and TSH; Advia Centaur FSH, fT4; Architect LH; FSH). Immulite 2000 fT4, TSH, testosterone and hCG (ALP-based) showed no interference. However, the presence of asfotase alfa resulted in a dose-dependent increase of Troponin I signal. CONCLUSION: The presence of asfotase alfa must be taken into consideration when analyzing blood samples in treated patients to avoid any risk of misinterpretation of false positive/negative results. It is essential that assays be tested for this possible interference.

[Infantile hypophosphatasia caused by a novel compound heterozygous mutation: a case report and pedigree analysis].

This article reported the clinical features of one child with infantile hypophosphatasia (HPP) and his pedigree information. The proband was a 5-month-old boy with multiple skeletal dysplasia (koilosternia, bending deformity of both radii, and knock-knee deformity of both knees), feeding difficulty, reduction in body weight, developmental delay, recurrent pneumonia and respiratory failure, and a significant reduction in blood alkaline phosphatase. Among his parents, sister, uncle, and aunt (other family members did not cooperate with us in the examination), his parents and aunt had a slight reduction in alkaline phosphatase and his aunt had scoliosis; there were no other clinical phenotypes or abnormal laboratory testing results. His ALPL gene mutation came from c.228delG mutation in his mother and c.407G>A compound heterozygous mutation in his father. His aunt carried c.228delG mutation. The c.407G>A mutation had been reported as the pathogenic mutation of HPP, and c.228delG mutation was a novel pathogenic mutation. Hypophosphatasia is caused by ALPL gene mutation, and ALPL gene detection is an effective diagnostic method. This study expands the mutation spectrum of ALPL gene and provides a theoretical basis for genetic diagnosis of this disease.

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: the contribution of imaging.

Radiography and imaging are necessary for the diagnosis of hypophosphatasia (HPP) at all stages of life, from the antenatal period to the complications of adulthood, and in the forms of variable severity. The consequences of alkaline phosphatase activity deficiency, namely defective mineralization and bone fragility, may be detected by radiological tools and share features that distinguish them from other diseases responsible for mineralization defects. Radiography and imaging are also fundamental for the screening and diagnosis of the complications of HPP, some of which are related to the episodes of hypercalcemia and hyperphosphatemia (nephrocalcinosis). Radiologists should be aware of the particularities of HPP to efficiently orient the patients toward optimal medical care.

Phosphate homeostasis and disorders.

Recent studies of inherited disorders of phosphate metabolism have shed new light on the understanding of phosphate metabolism. Phosphate has important functions in the body and several mechanisms have evolved to regulate phosphate balance including vitamin D, parathyroid hormone and phosphatonins such as fibroblast growth factor-23 (FGF23). Disorders of phosphate homeostasis leading to hypo- and hyperphosphataemia are common and have clinical and biochemical consequences. Notably, recent studies have linked hyperphosphataemia with an increased risk of cardiovascular disease. This review outlines the recent advances in the understanding of phosphate homeostasis and describes the causes, investigation and management of hypo- and hyperphosphataemia.

[Enzyme replacement therapy for hypophosphatasia].

Hypophosphatasia is caused by abnormal tissue-nonspecific alkaline phosphatase (ALP), leading to impaired calcification in bone. Patients with severe hypophosphatasia have difficulties in respiratory function from early days after birth and the rate of lethality is extremely high. Enzyme replacement therapy using bone-targeting recombinant ALP, which has 10 aspartic acids in the C-terminal tail has developed. The efficacy of ERT was firstly observed in model mice of hypophosphatasia. In clinical trial including perinatal and infantile types of hypophosphatasia, efficacy and safety have been reported. Expanded clinical trial is underway and the results of the clinical trial might be reported by the end of the next year.

Acute hypophosphatasemia.

UNLABELLED: The temporal evolution of a low serum alkaline phosphatase value may relate to its cause. Precipitous lowering of serum alkaline phosphatase below the lower range of normal is uncommon and may indicate severe physiologic stress and increased short-term mortality. INTRODUCTION: The differential diagnosis of a low serum alkaline phosphatase (ALP) value (hypophosphatasemia) is wide ranging, anecdotal, and unfamiliar. The temporal evolution of hypophosphatasemia may relate to its cause. The purpose of this study is to report conditions and circumstances associated with precipitous lowering of serum ALP below the lower range of normal. METHODS: Marshfield Clinic IRB approved use of their electronic medical record to search for subjects with at least two serum ALP values ≤ 40 U/L (normal 40-125 U/L). When the temporal evolution of the qualifying ALP values indicated a precipitous lowering from usually normal serum ALP values, the subject was deemed to have acute hypophosphatasemia. Thirty years of laboratory data and 10 years of clinical narrative were analyzed. Associated diagnoses, clinical circumstances, and short-term mortality were recorded. RESULTS: A total of 458,767 subjects had 2,584,051 serum ALP values, and 5,190 (1.1 %) subjects had at least two serum values ≤ 40 U/L. A detailed review of 1,276 subjects selected on the basis of their lowest ALP value and age identified 190 subjects with acute hypophosphatasemia. Acute hypophosphatasemia was recorded during periods of major trauma/surgery, multisystem failure, acute anemia, blood product transfusions (often massive), apheresis, hypomagnesemia, and acute caloric restriction. Twenty-eight subjects (15 %) died within 35 days of their nadir serum ALP. CONCLUSION: Acute hypophosphatasemia is associated with profound illness or physiologic stress and followed by increased short-term mortality. The temporal evolution of hypophosphatasemia may relate to its cause.

[Clinical condition and therapy of bone diseases].

Skeletal dysplasia is the term which represents disorders including growth and differentiation of bone, cartilage and ligament. A lot of diseases are included, and new disorders have been added. However, the therapy of most bone diseases is less well-established. Achondroplasia, hypochondroplasia, and osteogenesis imperfecta are most frequent bone diseases. There is no curative treatment for these diseases, however, supportive therapies are available ; for example, growth-hormone therapy for achondroplasia and hypochondroplasia, and bisphosphonate therapy for osteogenesis imperfecta. In addition, enzyme replacement therapy for hypophosphatasia is now on clinical trial.

Tumor mesenquimatoso fosfatúrico de fosa nasal con compromiso intracraneano: reporte de un caso y revisión de la literatura / Nasal fossa phosphaturic mesenchymal tumor with intracraneal compromise: case report and review of the literature

El tumor mesenquimatoso fosfatúrico (TMF) es una enfermedad extremadamente rara. Según evidencia reciente es causado por la sobreexpresión del factor de crecimiento fibroblástico 23 (FGF23), el cual genera hipofosfemia y osteomalacia. A continuación presentamos el caso de un paciente de 42 años con un tumor mesenquimatoso fosfatúrico de fosa nasal izquierda con extenso compromiso intracraneano. Cabe destacar que hasta la fecha hay 142 casos reportados de TMF en la literatura de los cuales solo 11 se ubican en fosa nasaly cavidades sinusales, y sólo dos de ellos ubicados en fosa nasal¹. El paciente tuvo una exitosa resolución quirúrgica con la consecuente normalización de parámetros analíticos (incluido el FGF23), mejoría sintomática y ausenia de recidiva hasta la fecha.

The phosphaturic mesenchymal tumor (PMT) is an extremely rare disease. According to recent evidence is caused by overexpression of fibroblast growth factor 23 (FGF23) which generates hypophosphatemia and osteomalacia. We report the case of a 42 year old patient with a left nasal fossa phosphaturic mesenchymal tumor with intracranial involvement. Should be noted that to date there are 142 reported cases of PMT in the literature of which only 11 are located in nasal fossa and sinus cavities, two of them located in nasal fossa¹. The patient had a successful surgical resolution with consequent normalization of analytical parameters (including FGF23), absence of symptoms and no recurrence to date.

[Genetic basis for skeletal disease. Clinical characteristics of hypophosphatasia and its treatment].

Hypophosphatsia is caused by the defect of tissue-nonspecific alkaline phosphatase (ALP), and exhibits hypomineralization of skeleton and rachitic change of bone. The most severe form of hypophosphatasia is a perinatal form, which is also called a lethal form. However, some patients of this form can survive due to advances in neonatology. Other forms consist of infantile, childhood, adult and odonto types. Conventional therapies for hypophosphatasia are administration of vitamin B6 for convulsion and low calcium-containing milk for hypercalcemia. Bone marrow transplantation has been reported to treat several patients with hypophosphatasia. However, the method must be developed which improves the survival of donor mesenchymal cells in patients. Recombinant bone-targeted ALP therapy is now on clinical trial in Canada and U.S.A and expected to be available in near future.

[Neonatal hypophosphatasia].

Hypophosphatasia is a rare inborn disease of metabolism. This paper reviewed its pathogenesis, forms, clinical manifestations, differential diagnosis,treatment and prognosis. Here a case of neonatal hypophosphatasia is reported. This baby was female (30 minutes old). Prenatal ultrasound showed disproportionate biparietal diameter and long bones of limbs in the baby. After birth, she presented with obvious craniomalacia, respiratory distress and cyanosis. Serum alkaline phosphatase level was significantly reduced. Both X-ray and autopsy showed extremely insufficient skeletal mineralization. Four days later she died of respiratory failure.

[Biological activity of FGF-23 and pathophysiologic role in chronic kidney disease].

Recent studies indicate that FGF-23, which was originally identified as an endogenous causative factor for hypophosphatemic diseases, is a physiologic factor for the regulation of phosphate homeostasis and vitamin D metabolism. In patients with renal failure, serum concentrations of FGF-23 positively correlate with serum levels of phosphate, Ca-P product, and prathyroid hormone. It is plausible that increased FGF-23 levels are responsible for the reduction of 1,25(OH)2D levels in the early stage of renal insufficiency and also involved in the development of secondary hyperparathyroidism in chronic and end-stage kidney disease.

Manifestaciones maxilofaciales del raquitismo hipofosfatémico: reporte de un caso clínico / Maxillofacial manifestations of hypophosphatemic rickets: report of a clinical case

El raquitismo hipofosfatémico es una alteración metabólica transmitida genéticamente (ligada al cromosoma X) en donde disminuye la reabsorción de fosfato en el túbulo proximal. Esta enfermedad se manifiesta con defectos en la mineralización de los tejidos esquelético y dentario. El caso clínico presentado en este artículo corresponde a un niño de 8 años de edad con eta alteración en la que se observan deformidades en las extremidades inferiores (piernas arqueadas), disminución de su talla y bucalmente en los tejidos blandos, se aprecia gingivitis generalizada y sondajes periodontales no mayores de 2 mm. En el aspecto dentario existe una relación molar en clase II de Angle, con pérdida prematura de los molares temporales y por consecuencia, erupción prematura de los premolares permanentes. Debido a la asociación con la deficiente formación dentaria y la historia familiar, podríamos suponer una asociación entre raquitismo hipofosfatémico y las periodontitis de inicio precoz

Intracellular retention and degradation of tissue-nonspecific alkaline phosphatase with a Gly317-->Asp substitution associated with lethal hypophosphatasia.

One point mutation which converts glycine-317 to aspartate of tissue-nonspecific alkaline phosphatase (TNSALP) was reported to be associated with lethal hypophosphatasia (Greenberg, C. R., et al. Genomics 17, 215-217, 1993). In order to define the molecular defect of TNSALP underlying the pathogenesis of hypophosphatasia, we have examined the biosynthesis of TNSALP with a Gly317-->Asp substitution. When expressed in COS-1 cells, the mutant did not exhibit alkaline phosphatase activity at all, indicating that the replacement of glycine-317 with aspartate abolishes the catalytic activity of TNSALP. Pulse-chase experiments showed that the newly synthesized mutant failed to acquire Endo H-resistance and to reach the cell surface. Interestingly, this TNSALP mutant was found to form a disulfide-bonded high-molecular-mass aggregate and was rapidly degraded within the cell, though the mutant protein was modified by glycosylphosphatidylinositol (GPI). Lactacystin, an inhibitor of the proteasome, obstructed the degradation of the mutant protein, suggesting the involvement of proteasome as a part of quality control of TNSALP.

[Childhood hypophosphatasia]. / Hypofosfatasemie op de kinderleeftijd.

Hypophosphatasia was diagnosed in two boys aged four months and two years. This is a rare hereditary bone disease characterized by deficient activity of enzyme alkaline phosphatase. Increased levels of substrates of this enzyme are found: phosphoethanolamine in urine and pyridoxal phosphate in serum. Patients show defective bone mineralization, which results in severe deformities of limbs, thorax and skull and dental abnormalities (loss of teeth and caries). The disease is classified in four age-related forms: perinatal, infantile, childhood and adult hypophosphatasia. The perinatal form is usually lethal. There is no curative therapy. Recognition of the disease is of importance for genetic counselling.