Serum alkaline phosphatase can be elevated in patients with hypophosphatasia due to liver disease.

BACKGROUND: Hypophosphatasia (HPP) is a rare inherited disorder caused by pathogenic loss-of-function variants in the ALPL gene, encoding the tissue-nonspecific isoenzym of alkaline phosphatase (ALP; TNSALP). Low serum ALP is the biochemical hallmark of HPP, but it is unknown whether ALP levels can increase due to concurring liver disease, which may lead to a missed diagnose of HPP. We present a patient with genetically confirmed HPP, who showed a transient increase of serum ALP levels due to alcohol-induced hepatitis. CLINICAL REPORT: A 71-year old man was seen at our Bone Center for surveillance of HPP. Serum ALP was always low (23 U/L; reference value: <115 U/L). During follow-up, his serum ALP increased (156 U/L, further rising to 204 U/L), with concomitantly elevated serum gamma-glutamyl transferase and transaminases, and a rise in bone specific ALP (18.7 µg/L; reference value: 5.7-32.9 µg/L). This was attributed to alcohol-induced hepatitis. After refraining from alcohol intake, both serum ALP and bone specific ALP levels returned to initial low levels (30 U/L and 4.3 µg/L respectively). CONCLUSIONS: We demonstrated the history of a 71-year old patient with HPP, presenting during routine follow-up with an elevated serum ALP level up to 204 U/L due to alcohol-induced hepatitis. This case illustrates that the diagnosis of HPP can potentially be missed when ALP levels are normal or elevated due to a concomitant liver disease.

Prevalence of Low Serum Alkaline Phosphatase and Hypophosphatasia in Adult Patients with Atypical Femur Fractures.

Hypophosphatasia (HPP) is a rare genetic disorder characterized by low serum alkaline phosphatase (ALP), its manifestations may include atypical femoral fractures (AFF). However, the prevalence of low serum ALP and HPP in patients with AFF remains unknown. We retrospectively analyzed ALP levels and clinical manifestations compatible with HPP in 72 adult patients with confirmed AFF by chart review. ALP values were compared with those of a control group of patients with prior proximal femoral fracture during antiresorptive treatment (n = 20). Among the AFF patients, 18 (25%) had at least one serum ALP value ≤ 40 IU/L, although in all but one case, at least one ALP value > 40 IU/L was also detected at another time point. Most low ALP values were associated with antiresorptive treatment (P = 0.049) and lowest levels of ALP did not differ between the AFF and the control groups (P = 0.129). However, low ALP values among AFF patients were associated with a higher rate of bilateral AFF (50% vs 22%, P = 0.025), metatarsal fracture (33% vs 7%, P = 0.006), and with trends for more frequent use of glucocorticoid (22% vs 8%, P = 0.089) and proton pump inhibitor (61% vs 44%, P = 0.220). In one AFF patient with low ALP and clinical suspicion of HPP, a rare pathogenic heterozygous variant of the ALPL gene was identified. In conclusion, low ALP values are common among subjects with AFF and mainly related to concomitant antiresorptive medication. Hence, low serum ALP has low specificity for HPP among AFF patients.

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.

Clinical and molecular findings in children and young adults with persistent low alkaline phosphatase concentrations.

BACKGROUND: Hypophosphatasia is a rare inherited metabolic disease resulted by ALPL gene mutations. It is characterized by defective bone and teeth mineralization. The phenotypic spectrum is highly variable ranging from lethal perinatal form to mild forms which are only diagnosed in adulthood or remain undiagnosed despite persistently low concentrations of ALP. The aim of this study is to evaluate the clinical phenotype and frequency of ALPL mutations in a group of patient with hypophosphatasaemia. METHODS: Thirty individuals with alkaline phosphatase values below 40 IU/L in at least two assessments and having no alternative explanation for their low ALP concentrations were included in the study. The clinical features and radiological data of the study group were re-investigated for hypophosphatasia-related findings. ALPL sequence analysis was performed using Sanger sequencing. RESULTS: No patient in the study group had severe symptoms, nor had they initially been diagnosed as having hypophosphatasia. Four different heterozygous ALPL mutations (c.542C>T, c.648 + 1G>A, c.657G>T and c.862 + 1G>C) were found in four patients. One splice site mutation (c.862 + 1G>C) was reported for the first time in this study. CONCLUSION: ALPL sequence analysis may help to diagnosing genetic defects in individuals with persistently low ALP concentrations and provide to take preventive measures before symptoms appear. As in the other populations, HPP displays allelic heterogeneity in our population.

[Pediatric reference values for alkaline phosphatase and pathophysiological variations]. / Valeurs de référence de la phosphatase alcaline en pédiatrie et variations physiopathologiques.

Alkaline phosphatase activity is a parameter included in biochemical liver test. These isoenzymes are of various cellular origin inducing physiological variations on age and sex. The alkaline phosphatase activity standardization as well as numerous international studies have made it possible to standardize the pediatric reference values. The hyperphosphatasemia etiologies are very well know but the hypophosphatasemia are hardly explored and can allow the diagnosis of pathologies including hypophosphatasia, a rare treatable disease.

Adult hypophosphatasia manifests in a marathon runner.

A 49-year-old woman, previously healthy, presented with recurrent fractures provoked by minimal trauma. She had sustained seven fractures over the previous 2 years. While she was an avid runner, her injuries were determined to be out of proportion to the degree of trauma. Initial evaluation, exploring the more common causes such as low bone density and abnormal vitamin D metabolism, was unremarkable. On repeat of the some of the tests, a low alkaline phosphatase (AP) was noted, which raised suspicion for hypophosphatasia (HPP), a rare cause of recurrent fractures. Subsequent workup revealed a low bone-specific AP and elevated vitamin B6 Subsequently, genetic testing confirmed the diagnosis of adult-onset HPP caused by a heterozygous mutation c.407G>A in the ALPL gene. Asfotase alfa was started; however, the patient developed an allergic reaction leading to the discontinuation of the drug.

Mineral Intake and Clinical Symptoms in Adult Patients with Hypophosphatasia.

BACKGROUND: Hypophosphatasia (HPP) is a rare inherited metabolic disorder characterized by deficient activity of the tissue-nonspecific alkaline phosphatase entailing impaired turnover of phosphorus metabolites. Dietary mineral intake is suspected to influence clinical symptoms of HPP, but scientific evidence is missing. METHODS: Cross-sectional matched-pairs study collecting comprehensive data on nutrient intake in 20 HPP patients and 20 unaffected, age- and gender-matched controls. Dietary information and clinical symptoms were documented in detail over 7 consecutive days using structured diaries. RESULTS: Baseline data and type of energy-supplying nutrients were balanced between both groups. Median nutritional intake of phosphorus and calcium were significantly lower in HPP patients versus controls, which is partially attributable to lower energy consumption in HPP patients. Differences regarding phosphorus and calcium (Ca/P) ratio and uptake of magnesium, zinc, and vitamin B6 were not statistically significant. Both high (≥ 1375 mg/d) and low intakes (< 1100 mg/d) of phosphorus were significantly associated with an increased frequency of neuropsychiatric symptoms (P = 0.02). Similarly, very high and very low intake of calcium was significantly associated with musculoskeletal (P < 0.01), gastrointestinal (P = 0.02), and neuropsychiatric (P < 0.001) symptoms. An increased Ca/P ratio was associated with increased tiredness/fatigue (P < 0.01), whereas a decreased Ca/P was associated with gastrointestinal issues (P = 0.01). CONCLUSION: Phosphorus and calcium intake seem reduced in HPP patients along with reduced total energy consumption. Particularly high as well as very low absolute or unbalanced phosphorus and calcium intake are associated with an increased frequency of clinical symptoms.

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.

Association of ALPL variants with serum alkaline phosphatase and bone traits in the general Japanese population: The Nagahama Study.

Although alkaline phosphatase (ALP) activity is relatively low in carriers of recessive type hypophosphatasia (HPP), most are asymptomatic and therefore do not undergo medical evaluations. We analyzed the association of ALP-encoding ALPL variants with serum ALP and bone traits in the general Japanese population. Study participants (n = 9671) were from the Nagahama Study, which was a longitudinal cohort study of an apparently healthy general Japanese population. ALPL variants were analyzed by whole-genome sequencing or TaqMan probe assays using DNA extracted from peripheral blood samples. The speed of sound in calcaneal bone was assessed by quantitative ultrasound (QUS) and used as surrogate measures of bone mineral density. We identified 13 ALPL variants. Minor allele frequencies of three variants were higher than expected. Variant c.529G > A has been reported as a possible pathogenic variant for adult type HPP. Variants c.979C > T and c.1559delT are reported as pathogenic variants for perinatal severe HPP or infantile HPP. The allele frequencies of c.529G > A, c.979C > T, and c.1559delT were 0.0107, 0.0040, and 0.0014, respectively. Serum ALP activity was significantly lower and differed among the three variants (P < 0.001), as well as between individuals with and without any of the three variants (P < 0.001). Serum ALP activity was inversely associated with QUS values, although no direct association was observed between the ALPL variants and QUS values. An association between serum ALP activity and QUS was confirmed; however, we failed to detect an association between ALPL variants and bone traits in the general Japanese population.

Japanese nationwide survey of hypophosphatasia reveals prominent differences in genetic and dental findings between odonto and non-odonto types.

Hypophosphatasia (HPP) is a rare and intractable metabolic bone disease caused by mutations in the ALPL gene. Here, we undertook a nationwide survey of HPP in Japan, specifically regarding the prominent genetic and dental manifestations of odonto (n = 16 cases) and other (termed "non-odonto") (n = 36 cases) types. Mean serum alkaline phosphatase (ALP) values in odonto-type patients were significantly greater than those of non-odonto-type patients (P<0.05). Autosomal dominant and autosomal recessive inheritance patterns were detected, respectively, in 89% of odonto-type and 96% of non-odonto-type patients. The ALPL "c.1559delT" mutation, associated with extremely low ALP activity, was found in approximately 70% of cases. Regarding dental manifestations, all patients classified as odonto-type showed early exfoliation of the primary teeth significantly more frequently than patients classified as non-odonto-type (100% vs. 56%; P<0.05). Tooth hypomineralisation was detected in 42% of non-odonto-type patients, but not in any odonto-type patients (0%; P<0.05). Collectively, these results suggest that genetic and dental manifestations of patients with odonto-type and non-odonto-type HPP are significantly different, and these differences should be considered during clinical treatment of patients with HPP.

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.

Recurrent abducens nerve palsy and hypophosphatasia syndrome.

A 47-year-old woman presented with six episodes of horizontal binocular double vision over a 2-year period. CT imaging was significant for extensive dural calcification in the spine and calcification of the skull base, likely involving Dorello's canal. Biochemical testing revealed a persistently low alkaline phosphatase level. Recurrent nerve palsy may possibly be induced by mechanical compression of the sixth cranial nerve in Dorello's canal from calcification due to hypophosphatasia syndrome.

Adult hypophosphatasia with compound heterozygous p.Phe327Leu missense and c.1559delT frameshift mutations in tissue-nonspecific alkaline phosphatase gene: a case report.

BACKGROUND: Hypophosphatasia is an inherited bone disease characterized by low alkaline phosphatase activity encoded by ALPL. Clinically, hypophosphatasia can be categorized as perinatal, infantile, childhood, and adult forms, as well as odonto-hypophosphatasia, according to the age at first sign or dental manifestations. Adult hypophosphatasia typically presents in middle-aged patients who appear to be in good health in early adulthood and manifests as painful feet caused by recurrent, slow-healing stress fractures of the lower limb. Because the symptoms of adult hypophosphatasia vary and are common, many patients with hypophosphatasia might be not diagnosed accurately and thus may receive inappropriate treatment. CASE PRESENTATION: We report a case of a 35-year-old Japanese woman with low serum alkaline phosphatase detected at a routine medical checkup. She had mild muscle/bone pain but no history of rickets, fractures, or dental problems. Measurement of bone mineral density of the lumbar spine and the femoral neck revealed osteopenia below the expected range for age in a young adult. Abdominal ultrasonography revealed numerous microcalcifications in both kidneys. Analysis of amino acids in urine revealed that phosphoethanolamine was elevated. Low serum alkaline phosphatase activity, elevation of phosphoethanolamine, and low bone mineral density supported the diagnosis of hypophosphatasia. ALPL mutation analysis revealed two mutations: p.Phe327Leu and c.1559delT. These genetic abnormalities were previously reported in perinatal, infantile, and childhood but not adult hypophosphatasia. On the basis of the clinical presentation, laboratory and imaging findings, and genetic analyses, the patient was definitively diagnosed with adult hypophosphatasia. To the best of our knowledge, this is the first case report of adult hypophosphatasia with the compound heterozygous mutations p.Phe327Leu and c.1559delT. CONCLUSIONS: Although the risk of bone fracture was high in this case, treatment approaches differ between osteoporosis and hypophosphatasia. Because adult hypophosphatasia diagnosis is often difficult because of their varied symptoms, hypophosphatasia should be considered in the differential diagnosis of low serum alkaline phosphatase. Early diagnosis is important so that appropriate treatment can be initiated.

Natural History of Perinatal and Infantile Hypophosphatasia: A Retrospective Study.

OBJECTIVE: To report clinical characteristics and medical history data obtained retrospectively for a large cohort of pediatric patients with perinatal and infantile hypophosphatasia. STUDY DESIGN: Medical records from academic medical centers known to diagnose and/or treat hypophosphatasia were reviewed. Patients born between 1970 and 2011 with hypophosphatasia and any of the following signs/symptoms at age <6 months were eligible: vitamin B6-dependent seizures, respiratory compromise, or rachitic chest deformity (NCT01419028). Patient demographics and characteristics, respiratory support requirements, invasive ventilator-free survival, and further complications of hypophosphatasia were followed for up to the first 5 years of life. RESULTS: Forty-eight patients represented 12 study sites in 7 countries; 13 patients were alive, and 35 were dead (including 1 stillborn). Chest deformity, respiratory distress, respiratory failure (as conditioned by the eligibility criteria), failure to thrive, and elevated calcium levels were present in >70% of patients between birth and age 5 years. Vitamin B6-dependent seizures and respiratory distress and failure were associated significantly (P < .05) with the risk of early death. Serum alkaline phosphatase activity in all 41 patients tested (mean [SD]: 18.1 [15.4] U/L) was below the mean lower limit of normal of the reference ranges of the various laboratories (88.2 U/L). Among the 45 patients with relevant data, 29 had received respiratory support, of whom 26 had died at the time of data collection. The likelihood of invasive ventilator-free survival for this cohort decreased to 63% at 3 months, 54% at 6 months, 31% at 12 months, and 25% at 5 years. CONCLUSIONS: Patients with perinatal or infantile hypophosphatasia and vitamin B6-dependent seizures, with or without significant respiratory distress or chest deformities, have high morbidity and mortality in the first 5 years of life. TRIAL REGISTRATION: ClinicalTrials.gov: NCT01419028.

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.

Pyridoxal 5'-phosphate and related metabolites in hypophosphatasia: Effects of enzyme replacement therapy.

OBJECTIVE: To investigate the utility of serum pyridoxal 5'-phosphate (PLP), pyridoxal (PL), and 4-pyridoxic acid (PA) as a diagnostic marker of hypophosphatasia (HPP) and an indicator of the effect of, and patient compliance with, enzyme replacement therapy (ERT), we measured PLP, PL, and PA concentrations in serum samples from HPP patients with and without ERT. METHODS: Blood samples were collected from HPP patients and serum was frozen as soon as possible (mostly within one hour). PLP, PL, and PA concentrations were analyzed using high-performance liquid chromatography with fluorescence detection after pre-column derivatization by semicarbazide. We investigated which metabolites are associated with clinical phenotypes and how these metabolites change with ERT. RESULTS: Serum samples from 20 HPP patients were analyzed. The PLP-to-PL ratio and PLP concentration were elevated in all HPP patients. They correlated negatively with serum alkaline phosphatase (ALP) activity and showed higher values in more severe phenotypes (perinatal severe and infantile HPP) compared with other phenotypes. PL concentration was reduced only in perinatal severe HPP. ERT reduced the PLP-to-PL ratio to mildly reduced or low-normal levels and the PLP concentration was reduced to normal or mildly elevated levels. Urine phosphoethanolamine (PEA) concentration did not return to normal levels with ERT in most patients. CONCLUSIONS: The serum PLP-to-PL ratio is a better indicator of the effect of ERT for HPP than serum PLP and urine PEA concentrations, and a PLP-to-PL ratio of <4.0 is a good indicator of the effect of, and patient compliance with, ERT.

Abnormal bone turnover in individuals with low serum alkaline phosphatase.

The clinical spectrum of hypophosphatasia (HPP) is broad and variable within families. Along severe infantile forms, adult forms with mild manifestations may be incidentally discovered by the presence of low alkaline phosphatase (ALP) activity in serum. However, it is still unclear whether individuals with persistently low levels of ALP, in the absence of overt manifestations of HPP, have subclinical abnormalities of bone remodeling or bone mass. The aim of this study was to obtain a better understanding of the skeletal phenotype of adults with low ALP by analyzing bone mineral density (BMD), bone microarchitecture (trabecular bone score, TBS), and bone turnover markers (P1NP and ß-crosslaps). We studied 42 individuals with persistently low serum ALP. They showed lower levels of P1NP (31.4 ± 13.7 versus 48.9 ± 24.4 ng/ml; p = 0.0002) and ß-crosslaps (0.21 ± 0.17 versus 0.34 ± 0.22 ng/ml, p = 0.0015) than individuals in the control group. There were no significant differences in BMD, bone mineral content, or TBS. These data suggest that individuals with hypophosphatasemia have an overall reduction of bone turnover, even in the absence of overt manifestations of HPP or low BMD. We evaluated bone mineral density (BMD), bone microarchitecture, and bone turnover markers in patients with low serum levels of alkaline phosphatase. Our results show that these patients have low bone remodeling even in the absence of BMD abnormalities, thus supporting the recommendation of avoiding antiresorptives such as bisphosphonates in these subjects.

Spurious testosterone laboratory results in a patient taking synthetic alkaline phosphatase (asfotase alfa).

OBJECTIVES: We report a case of discordant total and free testosterone values in a patient with hypogonadism and juvenile hypophosphatasia after he initiated treatment with asfotase alfa, recombinant tissue non-specific alkaline phosphatase. METHODS: Total testosterone was evaluated using immunoassay pre and post initiation of therapy with asfotase alfa, and free testosterone was evaluated using radioimmunoassay and LC-MS/MS while on asfotase alfa therapy. RESULTS: Total testosterone measured by immunoassay was normal prior to therapy with asfotase alfa, and was low post initiation of therapy. During the same time frame, free testosterone measured using RAI and total testosterone measured using LC-MS/MS were normal on asfotase alfa therapy. This suggests assay interference with the total testosterone immunoassay. CONCLUSION: When laboratory results are discordant or do not match the clinical impression, the possibility of assay interference should be considered. Alternative laboratory methods free of the interference should be selected to evaluate these patients. HUMAN GENES DISCUSSED IN THE PAPER: ALPL gene, Approved name: Alkaline phosphatase, liver/bone/kidney, Synonym: Tissue non-specific alkaline phosphatase (TNSAP).