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.

Asfotase Alfa Treatment Improves Survival for Perinatal and Infantile Hypophosphatasia.

CONTEXT: Hypophosphatasia (HPP) is an inborn error of metabolism that, in its most severe perinatal and infantile forms, results in 50-100% mortality, typically from respiratory complications. OBJECTIVES: Our objective was to better understand the effect of treatment with asfotase alfa, a first-in-class enzyme replacement therapy, on mortality in neonates and infants with severe HPP. DESIGN/SETTING: Data from patients with the perinatal and infantile forms of HPP in two ongoing, multicenter, multinational, open-label, phase 2 interventional studies of asfotase alfa treatment were compared with data from similar patients from a retrospective natural history study. PATIENTS: Thirty-seven treated patients (median treatment duration, 2.7 years) and 48 historical controls of similar chronological age and HPP characteristics. INTERVENTIONS: Treated patients received asfotase alfa as sc injections either 1 mg/kg six times per week or 2 mg/kg thrice weekly. MAIN OUTCOME MEASURES: Survival, skeletal health quantified radiographically on treatment, and ventilatory status were the main outcome measures for this study. RESULTS: Asfotase alfa was associated with improved survival in treated patients vs historical controls: 95% vs 42% at age 1 year and 84% vs 27% at age 5 years, respectively (P < .0001, Kaplan-Meier log-rank test). Whereas 5% (1/20) of the historical controls who required ventilatory assistance survived, 76% (16/21) of the ventilated and treated patients survived, among whom 75% (12/16) were weaned from ventilatory support. This better respiratory outcome accompanied radiographic improvements in skeletal mineralization and health. CONCLUSIONS: Asfotase alfa mineralizes the HPP skeleton, including the ribs, and improves respiratory function and survival in life-threatening perinatal and infantile HPP.

Prevention of Lethal Murine Hypophosphatasia by Neonatal Ex Vivo Gene Therapy Using Lentivirally Transduced Bone Marrow Cells.

Hypophosphatasia (HPP) is an inherited skeletal and dental disease caused by loss-of-function mutations in the gene that encodes tissue-nonspecific alkaline phosphatase (TNALP). The major symptoms of severe forms of the disease are bone defects, respiratory insufficiency, and epileptic seizures. In 2015, enzyme replacement therapy (ERT) using recombinant bone-targeted TNALP with deca-aspartate (D10) motif was approved to treat pediatric HPP patients in Japan, Canada, and Europe. However, the ERT requires repeated subcutaneous administration of the enzyme because of the short half-life in serum. In the present study, we evaluated the feasibility of neonatal ex vivo gene therapy in TNALP knockout (Akp2(-/-)) HPP mice using lentivirally transduced bone marrow cells (BMC) expressing bone-targeted TNALP in which a D10 sequence was linked to the C-terminus of soluble TNALP (TNALP-D10). The Akp2(-/-) mice usually die within 20 days because of growth failure, epileptic seizures, and hypomineralization. However, an intravenous transplantation of BMC expressing TNALP-D10 (ALP-BMC) into neonatal Akp2(-/-) mice prolonged survival of the mice with improved bone mineralization compared with untransduced BMC-transplanted Akp2(-/-) mice. The treated Akp2(-/-) mice were normal in appearance and experienced no seizures during the experimental period. The lentivirally transduced BMC were efficiently engrafted in the recipient mice and supplied TNALP-D10 continuously at a therapeutic level for at least 3 months. Moreover, TNALP-D10 overexpression did not affect multilineage reconstitution in the recipient mice. The plasma ALP activity was sustained at high levels in the treated mice, and tissue ALP activity was selectively detected on bone surfaces, not in the kidneys or other organs. No ectopic calcification was observed in the ALP-BMC-treated mice. These results indicate that lentivirally transduced BMC can serve as a reservoir for stem cell-based ERT to rescue the Akp2(-/-) phenotype. Neonatal ex vivo gene therapy thus appears to be a possible treatment option for treating severe HPP.

Infantile hypophosphatasia without bone deformities presenting with severe pyridoxine-resistant seizures.

An infant carrying a heterozygous c.43_46delACTA and a heterozygous c.668 G>A mutation in the ALPL gene with hypophosphatasia in the absence of bone deformities presented with therapy-resistant seizures. Pyridoxal phosphate was extremely high in CSF and plasma. Pyridoxine treatment had only a transient effect and the severe encephalopathy was fatal. Repeated brain MRIs showed progressive cerebral damage. The precise metabolic cause of the seizures remains unknown and pyridoxine treatment apparently does not cure the epilepsy.

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.

Neonatal hypophosphatasia and seizures. A case report.

Hypophosphatasia is a rare genetic disease characterized by deficiency of tissue-nonspecific alkaline phosphatase (TNSALP) activity, excessive urinary excretion of phosphoethanolamine, poor bone mineralization and skeletal anomalies. The shortage of alkaline phosphatase (ALP) alters the process of mineralization of skeleton causing a reduced transformation of phosphoethanolamine into phosphatidylethanolamine (cerebral phospholipid) with consequent high serum and urinary levels of phosphoethanolamine, a sensitive and highly specific marker for the disease. Four clinical forms have been described based on the age of onset with different courses and prognoses. An unusual case of lethal perinatal hypophosphatasia associated with seizures observed in a newborn admitted to Neonatal Intensive Care Unit of the University of Catania is described.

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.