Mutations In ALPL Gene Research Articles

Epidemiological, Clinical and Genetic Study of Hypophosphatasia in A Spanish Population: Identification of Two Novel Mutations in The Alpl Gene

Hypophosphatasia (HPP) is a genetic disease caused by one or several mutations in ALPL gene encoding the tissue-nonspecific alkaline phosphatase affecting the mineralization process. Due to its low prevalence and lack of recognition, this metabolic disorder is generally confused with other more frequent bone disorders. An assessment of serum total alkaline phosphatase (ALP) levels was performed in 78,590 subjects. Pyridoxal-5′-phosphate (PLP) concentrations were determined and ALPL gene was sequenced in patients potentially affected by HPP. Functional validation of the novel mutations found was performed using a cell-based assay. Our results showed persistently low serum ALP levels in 0.12% of subjects. Among the studied subjects, 40% presented with HPP-related symptoms. Nine of them (~28%) had a history of fractures, 5 (~16%) subjects showed chondrocalcinosis and 4 (~13%) subjects presented with dental abnormalities. Eleven subjects showed increased PLP concentrations. Seven of them showed ALPL gene mutations (2 of the mutations corresponded to novel genetic variants). In summary, we identified two novel ALPL gene mutations associated with adult HPP. Using this protocol, almost half of the studied patients were diagnosed with HPP. Based on these results, the estimated prevalence of mild HPP in Spain could be up to double than previously reported.

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

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

Ultrasound Diagnosis of Perinatal Lethal Hypophosphatasia, Confirmed with Targeted Next Generation Sequencing and Identification of a Novel Mutation in ALPL Gene

Perinatal lethal hypophosphatasia (p-HPP) is a lethal subtype of hypophosphatasia that prioritizes an early detection for appropriate treatment plan. Residual activity of alkaline phosphatase, owing to loss-of-function mutation of ALPL gene, accounts for degree of severity in phenotypes. We present a case of p-HPP in a Chinese couple’s fetus diagnosed at 18 weeks of gestation. Sonographic evaluation revealed a fetus with shortened and deformed limbs and hypoechogenic skull and vertebrae. After p-HPP was clinically diagnosed, the parents opted for medical termination of pregnancy. Further molecular investigation using next generation sequencing revealed the fetus to harbor a compound heterozygous mutation c935_943delTGGTGGTGG (pV313delVVV) and c406C>T (pR136C) in the ALPL gene. The mutation c935_943delTGGTGGTGG (pV313delVVV), of paternal origin, is to the best of our knowledge a novel mutation not reported before. This case demonstrates the importance of ultrasonography and molecular genetic testing in prenatal diagnosis.

Four novel mutations in the ALPL gene in Chinese patients with odonto, childhood, and adult hypophosphatasia.

Hypophosphatasia (HPP) is a rare inherited disorder characterized by defective bone and/or dental mineralization, and decreased serum alkaline phosphatase (ALP) activity. ALPL, the only gene related with HPP, encodes tissue non-specific ALP (TNSALP). Few studies were carried out in ALPL gene mutations in the Chinese population with HPP. The purpose of the present study is to elucidate the clinical and genetic characteristics of HPP in five unrelated Chinese families and two sporadic patients. Ten clinically diagnosed HPP patients from five unrelated Chinese families and two sporadic patients and fifty healthy controls were genetically investigated. All 12 exons and exon–intron boundaries of the ALPL gene were amplified by PCR and directly sequenced. The laboratory and radiological investigations were conducted simultaneously in these HPP ten patients. A 3D model of the TNSALP was used to predict the dominant negative effect of identified missense mutations. Three odonto, three childhood, and four adult types of HPP were clinically diagnosed. Ten mutations were identified in five unrelated Chinese families and two sporadic patients, including eight missense mutations and two frameshift mutations. Of which, four were novel: one frameshift mutation (p.R138Pfsx45); three missense mutations (p.C201R, p.V459A, p.C497S). No identical mutations and any other new ALPL mutations were found in unrelated 50 healthy controls. Our study demonstrated that the ALPL gene mutations are responsible for HPP in these Chinese families. These findings will be useful for clinicians to improve understanding of this heritable bone disorder.

Neurological and Neurosurgical Aspects of Hypophosphatasia

Hypophosphatasia is a rare hereditary progressive disease caused by a mutation in ALPL gene and characterized by low activity of alkaline phosphatase. Due to the disruption of the bone mineralization process, ricket-like deformations of the skeleton occur in the clinic picture more frequently but other systemic manifestations can be also observed as respiratory insufficiency, urinary tract damage, and neurological disorders. Seizures, delayed physical and psychomotor development, attention deficit disorder, muscle weakness, fatigue, intracranial hypertension associated with the development of craniosynostosis are revealed in these patients. The severity of the disease depends on age: the highest mortality is reported in younger patients, in perinatal and infantile forms of hypophosphatasia. Diagnosis is based on the identification of specific clinical manifestations: retardation of growth and development, skeletal deformities, pain in muscles and joints, premature tooth loss. In laboratory tests, a steady decrease in alkaline phosphatase level is detected taking into account age and sex specification. If possible, alkaline phosphatase substrates are measured: levels of pyridoxal-5-phosphate in the blood and phosphoethanolamine in urine are higher at low enzyme activity. Radiographs of long bones typically reveal characteristic ‘tongues’ of lucency projecting from growth plates into metaphyses, hypomineralization, osteopenia, various kinds of deformation. All patients with suspected hypophosphatasia should be consulted by a clinical geneticist and evaluated to identify possible mutation in the ALPL gene.

Incidence of Mutations in the ALPL, GGPS1, and CYP1A1 Genes in Patients With Atypical Femoral Fractures.

ABSTRACTAtypical femoral fractures (AFFs) are uncommon and often related to prolonged bisphosphonate (BP) treatment. Isolated cases have been linked to mutations of tissue nonspecific alkaline phosphatase (ALPL). Moreover, mutations in the geranylgeranyl pyrophosphate synthase (GGPPS) gene, which can be inhibited by BPs, and in the enzyme of the cytochrome P450 superfamily (CYP1A1), related to the metabolism of several drugs, have also been associated with AFF development. Our aim was to analyze the incidence of ALPL, GGPS1, and CYP1A1 gene mutations in patients with AFFs and their clinical characteristics. Seventeen women with AAFs were included. All patients underwent Sanger sequencing of the ALPL, GGPS1, and CYP1A1 genes, analyzing the presence of mutations and polymorphisms in these genes. The clinical characteristics of the patients, previous treatments, ALP substrates (vitamin B6 and phosphoethanolamine), bone turnover markers, and bone mass were also analyzed. Three of 17 patients (17.6%) presented heterozygous mutations in the ALPL (p.Gly288Ala) or CYP1A1 (p.Arg136His, p.Val409Ile) genes. Only the patient with the ALPL mutation presented increased ALP substrates. Patients with CYP1A1 variants had glucocorticoid‐induced osteoporosis. All patients were previously treated with BPs during 85.5 ± 38 months, and nearly 50% were also treated with glucocorticoids. The AFF was bilateral in 35% of cases. In conclusion, ALPL and CYP1A1 mutations may be related to the development of AFF in patients treated with BPs. The evaluation of ALP substrates in patients with low ALPL levels allows the identification of patients with hypophosphatasia. The role of CYP1A1 mutations in AFF needs further study. © 2018 The Authors. JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Clinical and Genetic Findings of Turkish Hypophosphatasia Cases.

Objective:Hypophosphatasia (HPP) is a rare, commonly unrecognized hereditary mineralization defect with a dramatically poor prognosis in severe cases. This study is the first to examine the detailed clinical and laboratory characteristics of patients with HPP and healthy carriers in Turkey.Methods:The study data were obtained retrospectively from the files of 10 healthy carriers and of 16 cases with HPP (12 children and 4 adults) who were followed in our center from 2012 to 2016.Results:The annual incidence of perinatal lethal hypophosphatasia (PLH) was estimated to be approximately 1 case per 435,517 live births,, which is the first report from Turkey. The clinical courses of the cases differed depending on the type of HPP. All of the seven cases (58.3% of all cases) with perinatal lethal form of HPP died. A need for respiratory support (p=0.001), a history of pyridoxine-dependent seizures (p=0.001), a low chest circumference measurement (p=0.017), younger age at diagnosis (p=0.029), a small head circumference at the time of presentation (p=0.042), a low arm span to height ratio (p=0.048), and a low serum alkaline phosphatase (ALP) level (p=0.042) seemed to be predicting factors for mortality. The mean height standard deviation score of the patients and those of the healthy carriers did not differ significantly (p=0.173). Different mutations were detected in nine of 14 cases (64.2%) in whom an ALPL gene mutation analysis could be performed, and five of these cases (35.7%) had novel mutations. The most common mutations were c746G>T (five alleles), c346G>A (three alleles), and c.140C>T (three alleles). In addition, the most frequently observed genotype in Turkish HPP cases was autosomal-dominant c.346G>A (p.A116T) mutations which were detected in three cases in two different families.Conclusion:Because of the respiratory problems, especially the lung hypoplasia, the clinical course is poor in cases with the perinatal lethal form of HPP. Some minor abnormalities such as mild short stature and osteopenia could be observed in asymptomatic heterozygote carriers. Laboratory findings were normal in these cases.

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.

New homozygous mutation in ALPL gene in Saudi patient with infantile hypophosphatasia

New homozygous mutation in ALPL gene in Saudi patient with infantile hypophosphatasia

Mutation analysis for two hypophosphatasia families with targeted next-generation sequencing

Objective: To detect the mutations in alkaline phosphatase (ALPL) gene of two Chinese families with perinatal hypophosphatasia (HPP), in order to explore the mechanism of this condition. Methods: Next-generation sequencing (NGS) of osteology system panel was carried out for exome sequencing in the mothers of 2 HPP fetuses, who visited Prenatal Diagnosis Center of the First Affiliated Hospital of Zhengzhou University. Further polymerase chain reaction (PCR) and Sanger sequencing validation was performed in the parents, affected fetuses and 200 unrelated healthy individuals to verify the mutation sites. Results: The mother and father of No.1 family carried ALPL gene c. 333delC (p.Gly112AlafsX10) and c. 568_570delAAC (p.190delAsn) base deletions, respectively. The affected fetus carried compound heterozygotes of the two mutations. Two mutations in ALPL gene known to be associated with hypophosphatasia were found in No.2 family, c. 1250A>G (p.Asn417Ser) in the mother and c. 1166C>A (p.Thr389Asn) in the father, while the fetus was a compound heterozygote carrying both of the two mutations. Both families met the pattern of autosomal recessive inheritance. ALPL gene c. 333delC (p.Gly112AlafsX10) was a novel mutation, and it was not found in the 200 unrelated healthy individuals. Conclusions: The mutations in ALPL gene may be the cause of HPP in the 2 families. NGS technology combined with Sanger sequencing could be an efficient and accurate diagnostic method.

A Diagnostic Algorithm for Children with Low Alkaline Phosphatase Activities: Lessons Learned from Laboratory Screening for Hypophosphatasia

To explore the role of laboratory screening for hypophosphatasia and propose a diagnostic pathway for children with low serum alkaline phosphatase (ALP) activities. A retrospective hospital-based study over an 8-year period was conducted to identify children younger than 16years of age with low ALP activity (<100 U/L). Study-positive patients were contacted for repeat sampling, and those with persistently low ALP had plasma pyridoxal-5'-phosphate and urinary phosphoethanolamine measured. Of 323 064 analyzed samples, 1526 had ALP activities <100 U/L. Most patients had transient hypophosphatasemia. Of 50 patients with last-recorded ALP <100 U/L, 32 were excluded given previous ALP >100 U/L. Eighteen were identified as study-positive. Of the 15 surviving children, 13 were traceable. Four had persistently low ALP activity on retesting, of whom 2 had raised pyridoxal-5'-phosphate and phosphoethanolamine concentrations and were subsequently tested for ALPL gene mutations; a 4-year-old asymptomatic girl with a novel homozygous ALPL missense mutation and a 23-year-old female with a heterozygous mutation. There was significant overlap in ALP activities between study-positive and 11 current patients with hypophosphatasia. We propose a diagnostic algorithm for children with low ALP activities based on clinical and biochemical variables. Patients with persistently low ALP activity require further clinical, biochemical, and radiological assessment for hypophosphatasia, even in the absence of clinical symptoms. The proposed diagnostic algorithm for children with low ALP will facilitate early detection of cases of hypophosphatasia, which, with the availability of enzyme replacement for hypophosphatasia, can be life-saving or avoid years of undiagnosed morbidity.

Improvement of the skeletal and dental hypophosphatasia phenotype in Alpl−/− mice by administration of soluble (non-targeted) chimeric alkaline phosphatase

Hypophosphatasia (HPP) results from ALPL gene mutations, which lead to a deficiency of tissue-nonspecific alkaline phosphatase (TNAP), and accumulation of inorganic pyrophosphate, a potent inhibitor of mineralization that is also a natural substrate of TNAP, in the extracellular space. HPP causes mineralization disorders including soft bones (rickets or osteomalacia) and defects in teeth and periodontal tissues. Enzyme replacement therapy using mineral-targeting recombinant TNAP has proven effective in preventing skeletal and dental defects in TNAP knockout (Alpl−/−) mice, a model for life-threatening HPP. Here, we show that the administration of a soluble, intestinal-like chimeric alkaline phosphatase (ChimAP) improves the manifestations of HPP in Alpl−/− mice. Mice received daily subcutaneous injections of ChimAP at doses of 1, 8 or 16mg/kg, from birth for up to 53days. Lifespan and body weight of Alpl−/− mice were normalized, and vitamin B6-associated seizures were absent with 16mg/kg/day of ChimAP. Radiographs, μCT and histological analyses documented improved mineralization in cortical and trabecular bone and secondary ossification centers in long bones of ChimAP16-treated mice. There was no evidence of craniosynostosis in the ChimAP16-treated mice and we did not detect ectopic calcification by radiography and histology in the aortas, stomachs, kidneys or lungs in any of the treatment groups. Molar tooth development and function improved with the highest ChimAP dose, including enamel, dentin, and tooth morphology. Cementum remained deficient and alveolar bone mineralization was reduced compared to controls, though ChimAP-treated Alpl−/− mice featured periodontal attachment and retained teeth. This study provides the first evidence for the pharmacological efficacy of ChimAP for use in the treatment of skeletal and dental manifestations of HPP.

Clinical and ALPL Gene Mutations Analysis in an Early Onset Chinese Odontohypophosphatasia Patient

Objective: To describe a Chinese case with novel frame shift ALPL gene mutation that results in infantile onset odontohypophosphatasia. Methods: Clinical data and genomic DNA of the patient and his parents were collected. Alkaline phosphatase gene (ALPL)of the patient and his parents were PCR following with sequencing. Results: The patient had premature exfoliation of primary teeth at 11 month, and showed no sign of development retardation or rickets in 3 years follow-up. Serum alkaline phosphatase was found significantly decreased. Sequence analysis of ALPL gene reveal a de novo heterozygous missense mutation in exon 10 c.1162T>C（p.Y371H）which has been reported previously. In addition, a heterozygous frameshift mutation in exon 12 c.1532insC（p. L511Pfs*272) was found in the patient and his mother. This inserted base causes a frame shift voiding the original stop codon. As a consequence, the original protein composed of 524 amino acids is translated into a protein with 783 amino acids. Conclusion: We report an early onset Chinese Odontohypophosphatasia patient, and a novel frame-shift mutation in exon 12, c.1532insC, p.L511Pfs*272）

Identification of the Mutations in the Tissue-nonspecific Alkaline Phosphatase Gene in Two Chinese Families with Hypophosphatasia

Hypophosphatasia is a genetic disorder characterized by defective bone and tooth mineralization and a deficiency of serum and bone alkaline phosphatase activity. To date, few studies have identified gene mutations in Chinese patients with hypophosphatasia. We sought to characterize the clinical manifestations and identify the mutations associated with the disease in Chinese hypophosphatasia patients. All 12 exons and the exon-intron boundaries of the ALPL gene were amplified and directly sequenced in two probands from unrelated Chinese families. The mutation sites were identified in other unaffected members of these two families and 100 healthy controls. In family 1, the proband displayed one novel splice site mutation, c.298-1G>A, which consisted of a homozygous G>A transition at nucleotide 298-1 in intron 4. The proband's mother displayed the heterozygous G/A ALPL gene mutation, but her father was identified as G/G homozygous. A paternity test ruled out false paternity and therefore confirmed that this splicing mutation occurred de novo either in the paternal germline or in the early development of the patient. In family 2, the proband revealed a novel missense mutation (c.1271T>C) in exon 11, which resulted in p.Val424Ala in the mature ALPL polypeptide. Furthermore, c.298-1G>A and c.1271T>C mutations were not found in unaffected family members of these two Chinese families and 100 unrelated controls. Our study shows that the novel de novo splicing mutation c.298-1G>A in intron 4 and the missense mutation c.1271T>C in exon 11 of the ALPL gene are responsible for hypophosphatasia in some Chinese patients.

Clinical utility gene card for: hypophosphatasia

1.5 Mutational spectrum Over 200 different disease-causing mutations have been reported in the ALPL gene mutations. Database: http://www.sesep.uvsq.fr/03_hypo_mutations.php. The distribution is as follows: 79% missense mutations; 10% small deletions; 4% splicing mutations; 3% nonsense mutations; 2% small insertions; and r1%: complex insertion/deletions, large deletions and mutations in the regulatory sequence. The large proportion of missense mutations with various effects on the enzymatic activity of alkaline phosphatase has been correlated with the high clinical variability.1 A part of missense mutations exhibits a dominant-negative effect,2–5 explaining dominant inheritance of mild forms of the disease.6–8

Parathyroid Hormone Treatment Improves Pain and Fracture Healing in Adult Hypophosphatasia

Adult hypophosphatasia (HPP) is characterized by low serum alkaline phosphatase (S-ALP) and poorly healing fractures due to ALPL gene mutations. Increased S-ALP and fracture repair were reported in two patients treated with teriparatide, PTH 1-34. The effects of full-length PTH 1-84 have not been studied. Two 56- and 64-yr-old sisters (patients 1 and 2) with HPP and with long-standing, painful femur fractures received PTH 1-84 (Preotact, 100 μg/d sc) for 7 and 18 months, respectively. Patient 1 had another treatment 8 months later because of new femur fractures. We characterized the underlying mutation(s) and treatment effects according to S-ALP, bone markers, serum ionized calcium, plasma phosphate (P-Pi), pain, mobility, and fracture healing. Both patients were compound heterozygotes for a p.G339R and p.E191K ALPL mutation. S-ALP increased significantly, 4.9- and 6.8-fold in patient 1 and 2.7-fold in patient 2. Responses decreased at 6 months but remained higher than basal activity. Serum N-terminal propeptide of type I procollagen and urinary N-telopeptide of type I collagen increased 14- to 19-fold and 9-5-fold in patient 1, respectively, and 9- and 3-fold in patient 2. P-Pi fluctuated in patient 1 and increased in patient 2. Pain and mobility improved promptly. Fractures healed after 7-8 months of treatment in patient 1 and at 15 months in patient 2. PTH 1-84 improves pain, mobility, and fracture repair in adult HPP, even after repeat treatment. Residual activity of the p.E191K ALPL gene mutation could explain why PTH can stimulate S-ALP. P-Pi concentrations may modulate the response.

Mild forms of hypophosphatasia mostly result from dominant negative effect of severe alleles or from compound heterozygosity for severe and moderate alleles

BackgroundMild hypophosphatasia (HPP) phenotype may result from ALPL gene mutations exhibiting residual alkaline phosphatase activity or from severe heterozygous mutations exhibiting a dominant negative effect. In order to determine the cause of our failure to detect a second mutation by sequencing in patients with mild HPP and carrying on a single heterozygous mutation, we tested the possible dominant effect of 35 mutations carried by these patients.MethodsWe tested the mutations by site-directed mutagenesis. We also genotyped 8 exonic and intronic ALPL gene polymorphisms in the patients and in a control group in order to detect the possible existence of a recurrent intronic mild mutation.ResultsWe found that most of the tested mutations exhibit a dominant negative effect that may account for the mild HPP phenotype, and that for at least some of the patients, a second mutation in linkage disequilibrium with a particular haplotype could not be ruled out.ConclusionMild HPP results in part from compound heterozygosity for severe and moderate mutations, but also in a large part from heterozygous mutations with a dominant negative effect.

Severe hypophosphatasia: characterization of fifteen novel mutations in the ALPL gene.

Hypophosphatasia is an inherited disorder characterized by defective bone mineralization and deficiency of serum and tissue liver/bone/kidney alkaline phosphatase (L/B/K ALP) activity. We report the characterization of ALPL gene mutations in a series of 11 families from various origins affected by perinatal and infantile hypophosphatasia. Sixteen distinct mutations were found, fifteen of them not previously reported: M45V, G46R, 388-391delGTAA, 389delT, T131I, G145S, D172E, 662delG, G203A, R255L, 876-881delAGGGGA, 962delG, E294K, E435K, and A451T. This confirms that severe hypophosphatasia is due to a large spectrum of mutations in Caucasian populations.