Hypophosphatasia: is it an underdiagnosed disease even by expert physicians?

Administration of Bisphosphonate Preparations to Mice with Mild-type Hypophosphatasia Reduces the Quality of Spontaneous Locomotor Activity

Hypophosphatasia (HPP) is a congenital bone disease caused by tissue-nonspecific mutations in the alkaline phosphatase gene. It is classified into six types: severe perinatal, benign prenatal, infantile, pediatric, adult, and odonto. HPP with femoral hypoplasia on fetal ultrasonography, seizures, or early loss of primary teeth can be easily diagnosed. In contrast, pediatric, adult, and odonto types of HPP over 4 years of age are less likely to be diagnosed because they do not have typical symptoms. Consequently, it may be misdiagnosed as common osteoporosis, and treatments incompatible with HPP may be implemented. The purpose of this study was to analyze the effects of bisphosphonate preparations administration on the femur of Akp2+/- mice, a mild-type HPP mice model. Zoledronic acid (Zol) was subcutaneously administered to 4-week-old Akp2+/- mice at 1 mg/kg (volume: 200 μL) once a week for a total of 5 times. Afterward, spontaneous locomotor activity analysis was performed, and serum and femur bones were collected at 9 weeks of age. Additionally, micro-computed tomography (CT) analysis, histological analysis, and analysis of the expression levels of various marker proteins and genes were performed. Age-matched Akp2+/+ mice served as controls. The results demonstrated that the administration of Zol to Akp2+/- mice, compared to Akp2+/+ mice, insufficiently promotive bone formation, torn femoral head cartilage, and decreased spontaneous locomotor activity. Therefore, it is important to accurately diagnose patients with mild-type HPP.

Could Some Patients With Fibromyalgia Potentially Have Hypophosphatasia? A Retrospective Single-Center Study

OBJECTIVE

Hypophosphatasia (HPP) is a rare disease characterized by incomplete or defective bone mineralization due to a mutation in the alkaline phosphatase (ALP) gene causing low levels of ALP. Disease presentation is heterogeneous and can present as a chronic pain syndrome like fibromyalgia (FM). Our objective was to determine if there are any potential patients with HPP in the group of patients who were diagnosed with FM. Antiresorptive therapy use can trigger atypical femur fractures in patients with HPP.

METHODS

We performed a retrospective chart review of all patients 18 years or older at a single academic center who were diagnosed with FM and had either a low or a normal ALP level. The following characteristics were reviewed: biological sex; age; history of fractures; diagnosis of osteoporosis, osteopenia, osteoarthritis, and chondrocalcinosis; genetic testing; vitamin B6 level testing; and medications.

RESULTS

Six hundred eleven patients with FM were identified. Two hundred had at least one low ALP level, and 57 had at least three consecutively low measurements of ALP, 44% of which had a history of fractures. No patients had vitamin B6 levels checked. None of the patients had previous genetic testing for HPP or underwent testing for zinc or magnesium levels.

CONCLUSION

The percentage of patients with FM who were found to have consistently low ALP levels was 9.3%. None had vitamin B6 level or genetic testing, suggesting that the diagnosis was not suspected. It is important to diagnose HPP given the availability of enzyme replacement therapy to prevent complications from HPP such as fractures. Our data support screening for this condition as a part of the initial workup of FM.

Atypical Femoral Fracture in Hypophosphatasia: A Systematic Review

Objective

To summarize the characteristics of all reported patients with hypophosphatasia (HPP) who sustained atypical femoral fracture (AFF) and identify all available evidence to quantify the rate of coexistence between HPP and AFF.

Methods

Potentially eligible articles were identified from the MEDLINE and EMBASE databases from its inception to September 2022, using a search strategy consisting of terms related to "Hypophosphatasia" and "Atypical femoral fracture." Eligible articles must report one of the following information: (1) individual data of patients diagnosed with HPP and AFF, (2) prevalence of HPP among patients with AFF, or (3) prevalence of AFF among patients of HPP. Characteristics of patients reported in each study were extracted.

Results

A total of 148 articles were identified. After the systematic review, 24 articles met the eligibility criteria. A total of 28 patients with AFF and HPP were identified. The mean ± SD age of the reported patients was 53.8 ± 12.5 years, and 22 patients (78.6%) were female. Nine patients (32.1%) received antiresorptive medication (bisphosphonate and/or denosumab), and two patients (7.1%) received teriparatide prior to the development of AFF. Seven (25.0%) and eighteen (64.3%) patients sustained unilateral and bilateral AFF, respectively (laterality not reported in three cases). Thirteen patients (46.4%) had a history of fractures at other sites. Four (14.3%) and seven (25.0%) patients received asfotase alfa and teriparatide after sustaining AFF. Two studies reported the prevalence of AFF among patients with HPP of approximately 10%. One study reported one HPP patient in a cohort of 72 patients with AFF.

Conclusions

Based on the limited evidence, AFF occurred in up to 10% of patients with HPP. Based on the 28 case reports, about two-thirds did not receive antiresorptive treatment, suggesting that the HPP itself could potentially be a risk factor for AFF.

Dental manifestation and management of hypophosphatasia

Hypophosphatasia is an inherited metabolic disorder characterized by defective mineralization of bones and teeth with a wide variety of manifestations, ranging from stillbirth to dental symptoms alone. Recently, the prognosis of severe hypophosphatasia patients has been greatly improved by the introduction of enzyme replacement therapy. The typical dental manifestation is early exfoliation of primary teeth due to disturbed cementum formation, so dentures are recommended to ensure that important oral functions are acquired. Some studies have shown that enzyme replacement therapy improves dental mineralization, resulting in the stabilization of periodontal tissues and better growth of tooth roots. A nationwide Japanese survey revealed the common genetic and dental manifestations of patients with mild hypophosphatasia, which markedly differ from those of the severe forms. There may be many undiagnosed mild patients, so dentists should contribute to the early diagnosis by screening possible cases based on the typical finding of early exfoliation of primary teeth. Early diagnosis is important for patients to receive early intervention in both medical and dental fields. The establishment of fundamental dental therapy to solve the dental problems is still underway and is eagerly anticipated.

Hypophosphatasia

Hypophosphatasia (HPP) is an inherited metabolic disease caused by loss-of-function mutations in the tissue non-specific alkaline phosphatase (TNAP) gene. Reduced activity of TNAP leads to the accumulation of its substrates, mainly inorganic pyrophosphate and pyridoxal-5′-phosphate, metabolic aberrations that largely explain the musculoskeletal and systemic features of the disease. More than 400 ALPL mutations, mostly missense, are reported to date, transmitted by either autosomal dominant or recessive mode. Severe disease is rare, with incidence ranging from 1:100,000 to 1:300,000 live births, while the estimated prevalence of the less severe adult form is estimated to be between 1:3100 to 1:508, in different countries in Europe. Presentation largely varies, ranging from death in utero to asymptomatic adults. In infants and children, clinical features include skeletal, respiratory and neurologic complications, while recurrent, poorly healing fractures, muscle weakness and arthropathy are common in adults. Persistently low serum alkaline phosphatase is the cardinal biochemical feature of the disease. Management requires a dedicated multidisciplinary team. In mild cases, treatment is usually symptomatic. Severe cases, with life-threating or debilitating complications, can be successfully treated with enzyme replacement therapy with asfotase alfa.