Adult Hypophosphatasia Research Articles

Lack of Sustained Response to Teriparatide in a Patient with Adult Hypophosphatasia

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. 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. 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. 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.

Atypical Femoral Fractures, Bisphosphonates, and Adult Hypophosphatasia

Lateral subtrochanteric femoral pseudofractures occurring in adults with osteomalacia from hypophosphatasia and X-linked hypophosphatemia support the hypothesis that atypical femoral fractures in osteoporosis treated with bisphosphonates also result from low bone turnover.

Bone-Targeted Replacement Therapy for Hypophosphatasia

Bone-Targeted Replacement Therapy for Hypophosphatasia

Novel Mouse Model of Autosomal Semidominant Adult Hypophosphatasia Has a Splice Site Mutation in the Tissue Nonspecific Alkaline Phosphatase Gene Akp2

Deactivating mutations in the TNSALP gene cause HPP. Akp2(-/-) mice model severe infantile HPP, but there is no model for the relatively mild adult form. Here we report on mice with an induced mutation in Akp2 that affects splicing. The phenotype of homozygotes mirror aspects of the adult form of HPP. Hypophosphatasia (HPP) is a clinically varied skeletal disorder resulting from deficiency of tissue nonspecific alkaline phosphatase (TNSALP). Mice lacking Akp2 model infantile HPP characterized by skeletal hypomineralization, impaired growth, seizures, and perinatal mortality. No animal model exists to study the less severe forms of the disease that typically present in later life. N-ethyl-N-nitrosourea (ENU) mutagenesis was used to generate mouse models of human disease. A mouse with low plasma alkaline phosphatase (ALP) activity was identified by our clinical chemistry screen. Its offspring were used for inheritance studies and subjected to biochemical, histological, and radiological phenotyping. DNA was extracted for mapping and osteoblasts harvested for functional studies. We showed semidominant inheritance of the low ALP phenotype and mapped the underlying point mutation to Akp2. Affected offspring bear the splice site mutation 862 + 5G>A-a hypomorphic allele named Akp2(Hpp). The same mutation has been reported in a patient. Akp2(Hpp/+) mice have approximately 50% of normal plasma ALP but display no other biochemical or skeletal abnormalities. Unlike Akp2(-/-) mice, Akp2(Hpp/Hpp) mice have normal initial skeletal development and growth, a normal lifespan and do not have seizures. TNSALP is low but detectable in Akp2(Hpp/Hpp) plasma. Osteoblasts display approximately 10% of normal ALP activity and reduced intracellular inorganic phosphate levels, yet are capable of normal mineralization in vitro. TNSALP substrates are significantly elevated in urine (inorganic pyrophosphate and phosphoethanolamine) and plasma (pyridoxal 5'-phosphate), whereas plasma inorganic pyrophosphate levels are normal. Akp2(Hpp/Hpp) mice develop late-onset skeletal disease, notably defective endochondral ossification and bone mineralization that leads to arthropathies of knees and shoulders. Akp2(Hpp/Hpp) mice mirror a number of clinical features of the human adult form of HPP. These mice provide for the first time an animal model of late onset HPP that will be valuable in future mechanistic studies and for the evaluation of therapies such as those aimed at HPP.

Chronic multifocal non-bacterial osteomyelitis in hypophosphatasia mimicking malignancy

BackgroundHypophosphatasia (HP) is characterized by a genetic defect in the tissue-nonspecific alkaline phosphatase (TNSALP) gene and predominantly an autosomal recessive trait. HP patients suffer from reduced bone mineralization. Biochemically, elevated concentrations of substrates of TNSALP, including pyridoxal-5'-phosphate and inorganic pyrophosphate occur in serum, tissues and urine. The latter has been associated with chronic inflammation and hyperprostaglandinism.Case presentationWe report on 2 affected children presenting with multifocal inflammatory bone lesions mimicking malignancy: A 6 years old girl with short stature had been treated with human growth hormone since 6 months. Then she started to complain about a painful swelling of her left cheek. MRI suggested a malignant bone lesion. Bone biopsy, however, revealed chronic inflammation. A bone scan showed a second rib lesion. Since biopsy was sterile, the descriptive diagnosis of chronic non-bacterial osteomyelitis (CNO) was established. The diagnostic tests related to growth failure were repeated and subsequent analyses demonstrated a molecular defect in the TNSALP gene. The second girl (10 years old) complained about back pain after she had fallen from her bike. X rays of her spine revealed compressions of 2 thoracic vertebrae. At first these were considered trauma related, however a bone scan did show an additional lesion in the right 4th rib. A biopsy of this rib revealed a sterile lympho- plasmocytoid osteomyelitis suggesting multifocal CNO. Further analyses did show a decreased TNSALP in leukocytes and elevated pyridoxal phosphate in plasma, suggesting a heterozygous carrier status of HP.ConclusionChronic bone oedema in adult HP and chronic hyper-prostaglandinism in childhood HP do suggest that in some HP patients bone inflammation is present in conjunction with the metabolic defect. Sterile multifocal osteomyelitis could be demonstrated. Non-steroidal anti-inflammatory treatment achieved complete remission. These cases illustrate chronic inflammation of the bone as a new feature of HP.

Adult Hypophosphatasia Treated with Teriparatide

Hypophosphatasia (HPP) features low serum alkaline phosphatase (ALP) activity (hypophosphatasemia) due to loss-of-function mutation within TNSALP, the gene that encodes "tissue-nonspecific" ALP (TNSALP). Consequently, inorganic pyrophosphate accumulates extracellularly and impairs skeletal mineralization. Affected adults manifest osteomalacia, often with slowly healing metatarsal stress fractures (MTSFs) and proximal femur pseudofractures. Pharmacotherapy remains elusive. A middle-aged woman sustained a slowly healing MTSF and then two enlarging MTSFs and a spontaneous proximal femur fracture. Pain persisted at all fracture sites. HPP was diagnosed as a result of low ALP activity (10-24 IU/liter; normal, 40-150 IU/liter) and elevated inorganic phosphate and pyridoxal 5'-phosphate concentrations in serum. Teriparatide (TPTD) (recombinant human PTH 1-34), 20 microg, was injected sc daily in an attempt to enhance osteoblast synthesis of TNSALP. Six weeks later, all fracture pain improved, and it resolved after 4 months. Radiographs of the enlarging MTSFs showed repair after 2-4 months. The femur fracture partially mended after 2 months and then healed. Additionally, hypophosphatasemia and hyperphosphatemia corrected, and biochemical markers of bone remodeling increased as long as TPTD (given for 18 months) was continued. The patient carried a heterozygous TNSALP missense mutation, p.D378V, which is common in the United States. This first HPP patient given TPTD demonstrated fracture repair accompanying correction of hypophosphatasemia and hyperphosphatemia and bone marker responses indicating enhanced skeletal remodeling. Increased TNSALP synthesis in bone together with lowered extracellular concentrations of inorganic phosphate (a competitive inhibitor of ALPs) seemed to improve her skeletal mineralization. Further evaluation of TPTD for HPP is warranted.

Different missense mutations at the tissue-nonspecific alkaline phosphatase gene locus in autosomal recessively inherited forms of mild and severe hypophosphatasia.

Hypophosphatasia is a heritable form of rickets/osteomalacia with extremely variable clinical expression. Severe forms are inherited in an autosomal recessive fashion; the mode of transmission of mild forms is uncertain. The biochemical hallmark of hypophosphatasia is deficient activity of the tissue-nonspecific isozyme of alkaline phosphatase (TNSALP). Previously, we demonstrated in one inbred infant that an identical missense mutation in both alleles of the gene encoding TNSALP caused lethal disease. We have now examined TNSALP cDNAs from four unrelated patients with the severe perinatal or infantile forms of hypophosphatasia. Each of the eight TNSALP alleles from these four individuals contains a different point mutation that causes an amino acid substitution. These base changes were not detected in at least 63 normal individuals and, thus, appear to be causes of hypophosphatasia in the four patients. (Two additional base substitutions, found in one allele from each of the four patients, are linked polymorphisms.) Twenty-three unrelated patients (of 50 screened), who reflect the entire clinical spectrum of hypophosphatasia, possess one of our of the above eight mutations. In two of these additional patients, mild forms of the disease are also inherited in an autosomal recessive fashion. Our findings indicate that hypophosphatasia can be caused by a number of different missense mutations and that the specific interactions of different TNSALP mutant alleles are probably important for determining clinical expression. Severe forms, perinatal and infantile disease, are largely the result of compound heterozygosity for different hypophosphatasia alleles. At least some cases of childhood and adult hypophosphatasia are inherited as autosomal recessive traits.

Hypophosphatasia in an adult: A case report.

In this rare case of adult hypophosphatasia, no radiological abnormalities of the skeletal system could be detected even by dual energy X-ray absorptiometry. Severe dental caries was the sole clinical manifestation, indicating this case as an "odontohypophosphatasia". The levels of serum osteocalcin were low, which may be a useful biochemical marker to diagnose hypophosphatasia. Southern blot analyses of the genomic DNA revealed no gross abnormalities. Thus, hypophosphatasia in this patient was presumed to be caused by point mutations or small deletions. In a review of previous reports, an increased incidence among women was found.

Management of femoral fractures and pseudofractures in adult hypophosphatasia.

Ten pseudofractures and six complete fractures occurred in five patients with adult hypophosphatasia. The four pseudofractures that were treated non-operatively progressed to complete fracture. The six pseudofractures and six complete fractures that were treated by internal fixation united. New fractures occurred in four patients after the removal of the internal fixation. We recommend that complete fractures, symptomatic pseudofractures, and progressive asymptomatic pseudofractures in patients with adult hypophosphatasia be treated with load-sharing internal-fixation devices, such as rigid intramedullary nails. These should not be removed unless it is absolutely essential. If removal is necessary, however, they should be replaced, preferably during the same anesthetic session. In our opinion, the guidelines developed from this study may be applied reasonably to patients with osteomalacia from causes other than hypophosphatasia, especially if medical therapy has been unsuccessful.

Inheritance of hypophosphatasia

A system of multiple, codominant alleles (H N, H C, H I) is proposed for the inheritance of hypophosphatasia. These alleles are associated with a single autosomal locus which determines the presence or absence of hypophosphatasia among human subjects. Either H C or H I conditions hypophosphatasia whereas H N conditions the absence of this disorder. Only one genotype, H NH N, produces the absence of hypophosphatasia. Either H NH C or H NH I produces adult hypophosphatasia. Either H CH C or H CH I produces childhood hypophosphatasia. Only H IH I produces infantile (neonatal) hypophosphatasia. H I is lethal only in a homozygous state. H N occurs at a much higher frequency in human populations than either H C or H I. Any one of the hypophosphatasic genotypes is thought to exert the same degree of epistatic effect on enzyme activity within the bone/liver/kidney complex of alkaline phosphatases. These alleles and genotypes are considered to be completely penetrant but show variable expressivity within each class of hypophosphatasia.

Adult hypophosphatasia without apparent skeletal disease: "odontohypophosphatasia" in four heterozygote members of a family.

Twenty members of a family with adult hypophosphatasia were examined clinically and biochemically. Severe caries causing early loss of permanent teeth was the only clinical symptom which could be attributed to hypophosphatasia. None of them had a history of defective bone mineralization, rachitic skeletal alterations, and recurrent pseudofractures or fractures. An iliac crest bone biopsy of the proposita showed a normal finding corresponding to the age of the patient. Four family members in two subsequent generations were affected, thus suggesting an autosomal dominant inheritance. Their serum and leukocyte alkaline phosphatases were reduced. The phosphoethanolamine (PEA) excretion in the urine was increased to a level which suggests a heterozygote state. The serum alkaline phosphatase activity could be ascribed to the liver isoenzyme fraction. This was shown by polyacrylamide electrophoresis, by inhibition studies with organ-specific inhibitors, heat inactivation, inhibition by antibodies, and treatment with neuraminidase. The proposita had an unexplained, diffuse fatty infiltration of the liver. Thus, not only alterations of bone but also of liver metabolism in hypophosphatasia should be considered. The variety of adult hypophosphatasia described in this paper is characterized by the lack of severe bone abnormalities, the apparently autosomal dominant inheritance, and the reduction of bone and intestinal isoenzyme in the serum. Our study suggests that hypophosphatasia is a heterogeneous disorder which includes both severe and clinically mild forms.

Hypophosphatasia

Histochemical and direct enzyme analysis of osseous tissue from 23 patients with hypophosphatasia revealed that all clinical forms of this inherited metabolic bone disease are characterized by deficiency of alkaline phosphatase (ALP) activity in bone. The severe infantile form has the most profound deficiency, infantile form has the most profound deficiency, yet the cellular source of this enzyme--osteoblasts and their matrix vesicles--are normal by routine light and electron microscopy. Despite radiographic changes in bone metaphyses consistent with rickets, iliac crest biopsy of one affected child revealed no abnormalities; the other had evidence of a mineralization defect, but not as severe as that in affected infants. In this child and several affected adults with osteomalacia, osteoblasts appeared flat and metabolically inactive. Although these histological changes suggested a different pathogenetic mechanism for adult and childhood hypophosphatasia, these changes are most likely secondary to the underlying osteomalacia. Our findings are most consistent with evidence that childhood and adult hypophosphatasia often represent clinical expression of the heterozygous state for ALP deficiency which, when homozygous, results in the clinically severe, recessive, infantile form. Histochemical and direct analysis of bone tissue from controls and patients with hypophosphatasia demonstrated that the severe infantile form is associated with the most severe ALP deficiency. In the milder clinical forms, ALP deficiency in bone is not as profound. In general, the severity of the clinical expression of hypophosphatasia reflects the magnitude of the deficiency of ALP in bone. This is the expected finding for this inborn error of metabolism, which illustrates the major role bone ALP activity has in the process of normal skeletal mineralization.

Adult hypophosphatasia with chondrocalcinosis and arthropathy: Variable penetrance of hypophosphatasemia in a large Oklahoma kindred

Three sisters, each with chondrocalcinosis/arthropathy, are described who have the clinical, laboratory and pathologic findings characteristic of the adult form of hypophosphatasia. Premature loss of adult teeth, arthralgias and pain from bilateral femoral pseudofractures were associated with subnormal circulating alkaline phosphatase levels, phosphoethanolaminuria and osteomalacia diagnosed by iliac crest biopsy. Assay of alkaline phosphatase activity in the blood of kindred members revealed hypophosphatasemia in one of two younger brothers. Several subjects in subsequent generations also had suspiciously tow alkaline phosphatase activity, but did not have histories of significant dental, bone or joint disease. Review of the medical records of the sisters' parents, aunts and uncles revealed normal alkaline phosphatase levels in their father and five of his siblings, but consistently low levels in their mother and two of her siblings. Despite hypophosphatasemia, the sisters' mother and her siblings lived to old age without clinical or radiographic evidence of bone disease. Our findings suggest that although adult hypophosphatasia can be transmitted as a dominant trait in some kindreds, there is considerable variation in the clinical expression of the biochemical defect. One person, generation or family may manifest clinical bone disease and arthropathy whereas the biochemical defect may be present but remain asymptomatic in others. Furthermore, in some cases, the adult form of hypophosphatasia may represent a developmental disorder with hypophosphatasemia appearing during adulthood.

Adult hypophosphatasia with chondrocalcinosis and orthopathy. Variable penetrance of hypophosphatemia in a large Oklahoma kindred: Whyte MP, Murphy WA, Fallon MD: Am J Med 1982; 72: 631–641

Adult hypophosphatasia with chondrocalcinosis and orthopathy. Variable penetrance of hypophosphatemia in a large Oklahoma kindred: Whyte MP, Murphy WA, Fallon MD: Am J Med 1982; 72: 631–641

Heterogeneity of Adult Hypophosphatasia Report of Severe and Mild Cases

Two cases of women with adult hypophosphatasia illustrate the clinical spectrum and potential difficulties in the diagnosis of this condition. Both patients had subnormal serum alkaline phosphatase activity, absence of leukocyte alkaline phosphatase, increased amounts of urinary phosphoethanolamine, and normal levels of immunoreactive calcitonin and parathyroid hormone. In undecalcified bone biopsy specimens, the number of osteoblasts and the tetracycline-labeled calcification front were similar in the two patients, although the percentage of unmineralized bone matrix and the extent of osteoid-covered bone surface were different. Twenty years of bone pain, severe skeletal deformities, and a generalized increase of osteoid in one patient contrasted with an 18-month history of bone pain and patchy osteoid in the other. These cases suggest that adult hypophosphatasia is a heterogeneous disorder and may be more common than previously realized.

Heterogeneity of adult hypophosphatasia. Report of severe and mild cases

Heterogeneity of adult hypophosphatasia. Report of severe and mild cases

Adult Hypophosphatasia

Investigation of the kindred of a 58-year-old woman with all of the features of "adult" hypophosphatasia revealed 12 individuals in 3 generations with subnormal circulating total alkaline phosphatase (AP) activity. The pattern of inheritance suggested autosomal dominant transmission, with incomplete penetrance of the trait particularly in the young males. Hypophosphatasic individuals other than the proposita were clinically well but had loss of permanent teeth, showing that dental abnormalities could be the only clinical manifestation of the disorder. Radiographic investigation of the proposita revealed that completion of stress fractures was necessary for healing; maturation of incomplete fractures resulted in stable Looser zones. Skeletal survey and radionuclide bone imaging were unremarkable in hypophosphatasic individuals without fracture. Subclinical osteopenia was found in several affected women by metacarpal cortical width and bone densitometric measurements. Laboratory studies showed increased plasma and urinary phosphoethanolamine levels in affected individuals. Phosphoethanolamine and phosphoserine appeared to be natural subtrates for AP since a negative correlation existed between each substrate and circulating total AP activity. Phosphoethanolamine and phosphoserine levels were greatest in the clinically affected proposita; furthermore, only she showed absence of leukocyte AP activity. Heat fractionation of her total circulating AP activity suggested severe reduction in the bone isoenzyme. Hypophosphatasic children had higher levels of total circulating AP than affected adults; the increase was apparently secondary to increased bone isoenzyme. Iliac crest bone biopsies showed greater abnormality in affected women. Osteoidosis was particularly pronounced in the proposita's younger affected sister and hypophosphatasic daughter. Histomorphometric analyses of the biopsies revealed a paucity of osteoblasts despite increased quantities of unmineralized matrix. The finding that hypophosphatasic children in this kindred had higher circulating total AP activity than adults and were able to model their skeleton normally, together with observations that the bone biopsy in adults had a paucity of osteoblasts, suggests that some factor(s) during growth is able to induce both AP activity and osteoblast function, or, that this disorder is an "abiotrophy" with deficient osteoblastic formation and/or accelerated destruction in adult life.

Orthopaedic problems in adult hypophosphatasia: a report of two cases

Hypophosphatasia in adults is rare. Two elderly sisters presenting with pathological fractures of the femur are reported to illustrate the difficulties in orthopaedic management of this disease. All patients with a history of repeated fractures, especially from minor trauma and with generalised radiological bony abnormality, should be screened for this rare disease. A consistently low level of serum alkaline phosphatase with the presence of phosphoethanolamine in the urine is diagnostic.

ADULT HYPOPHOSPHATASIA

Abstract A case of adult hypophosphatasia under treatment with a high orthophosphate (Pi) intake is described. The patient is a 53‐year‐old woman. Her symptoms have progressed for seven years, and it has been necessary to perform osteosynthesis of both crura. The diagnosis rests upon a characteristic clinical picture, low serum alkaline phosphatase activity, high urinary excretion of phosphoethanolamine, and an invariably elevated concentration of inorganic pyrophosphate (PPi) in plasma accompanied by a very high excretion of this compound in the urine. An improved technique allowed specific determinations of microquantities of PPi in biologic materials. The concentrations of PPi in plasma and urine remained unchanged when the patient's intake of phosphorus was increased to 1.98 g/day. The PPi/Pi ratio in the urine was 10–20 before treatment. During treatment Pi excretion increased, PPi excretion did not change, and the ratio decreased to around 7. The renal tubular transport of PPi probably was saturated, and therefore PPi, which was circulating in abnormally high concentrations in the patient's fluids, could not be removed by loading with Pi. Four months of treatment did not benefit the patient.

Metabolic observations in adult hypophosphatasia

A diagnosis of hypophosphatasia of the type which occurs in adults was established in a thirty-six year old white man who suffered an incomplete femoral fracture after minimal trauma. The diagnosis was established on the basis of consistently low serum alkaline phosphatase values, apparent absence of alkaline phosphatase activity in leukocytes, and an abnormally high urinary excretion of phosphorylethanolamine. In two prolonged metabolic balance studies during healing of the fracture it was noted that the patient was retaining calcium and phosphorus. The rate of retention of these minerals was not influenced by the administration of prednisone in three dosage levels or by stilbestrol. These drugs also failed to cause elevation of the low serum alkaline phosphatase, or to induce detectable alkaline phosphatase activity in leukocytes. The nitrogen balance varied with intake and the dosage of prednisone, and did not parallel the balance of calcium or phosphorus.