Mineral Intake and Clinical Symptoms in Adult Patients with Hypophosphatasia

Impact of Restricted Phosphorus, Calcium-adjusted Diet on Musculoskeletal and Mental Health in Hypophosphatasia

Context

Impairments in musculoskeletal and mental health are common in adults with Hypophosphatasia (HPP). Restricted phosphorus intake has been suggested to positively affect symptoms in HPP, but there is a lack of interventional evidence.

Objective

This work aimed to evaluate the effect of a phosphorus-restricted, calcium-adjusted diet on musculoskeletal and mental health in HPP.

Methods

A prospective, noncontrolled, single-center interventional study (NuSTEPS II) was conducted among outpatients at the Osteology Department, University of Wuerzburg, Germany. A total of 26 adults with an established HPP diagnosis received a standardized diet with a defined daily intake of phosphorus (1160-1240 mg/d) and calcium (870-930 mg/d) over 8 weeks. Main outcome measures were functional testing and patient-reported outcome measures.

Results

At 8 weeks, significant improvements were observed in usual gait speed (P = .028) and the chair-rise test (P = .019), while no significant changes were seen in the 6-minute walk test (P = .468) and the timed up-and-go test (P = .230). Pain was not significantly reduced according to the visual analog scale (VAS) (P = .061), pain subscale of the 36-Item Short-Form Health Survey (SF-36) (P = .346), and Pain Disability Index (P = .686). Further, there was a significant improvement in the SF-36 vitality subscale (P = .022) while all other subscales as well as the Lower Extremity Functional Scale (P = .670) and the Fatigue Assessment Scale (P = .392) did not change significantly. Adjustments of mineral intake were not associated with relevant alterations regarding the intake of energy and energy-supplying nutrients or body composition.

Conclusion

Adjusting phosphorus and calcium intake may positively affect individual symptoms in adults with HPP, but overall clinical effectiveness regarding major issues like pain and endurance appears limited.

Zinc and vitamin D deficiency and supplementation in hypophosphatasia patients - A retrospective study

Hypophosphatasia (HPP) is characterized by severe skeletal symptoms including mineralization defects, insufficiency fractures, and delayed facture healing or non-unions. HPP is caused by mutations of the tissue non-specific alkaline phosphatase (TNSALP). Zinc is a cofactor of TNSALP and vitamin D an important regulator of bone matrix mineralization. Data from this retrospective study indicates that deficiencies in zinc or vitamin D occur in HPP patients with a similar frequency as in the general population. While guidelines for repletion of these micronutrients have been established for the general population, the transferability of the efficacy and safety of these regiments to HPP patients still needed to be determined. We filtered for variant classification (ACMG 3-5, non-benign) and data completeness from a total cohort of 263 HPP patients. 73.5 % of this sub-cohort were vitamin D deficient while 27.2 % were zinc deficient. We retrospectively evaluated the effect of supplementation according to general guidelines in 10 patients with zinc-deficiency and 38 patients with vitamin d-deficiency. The treatments significantly raised serum zinc or vitamin D levels respectively. All other assessed disease markers (alkaline phosphatase, pyrodoxal-5-phosphate) or bone turnover markers (phosphate, calcium, parathyroid hormone, bone specific alkaline phosphatase, creatinine, desoxypyridinoline) remained unchanged. These results highlight that general guidelines for zinc and vitamin D repletion can be successfully applied to HPP patients in order to prevent deficiency symptoms without exacerbating the disease burden or causing adverse effects due to changes in bone and calcium homeostasis.

Identifying adult hypophosphatasia in the rheumatology unit

BACKGROUND

The most frequent manifestation in adult hypophosphatasia (HPP) is musculoskeletal pain. The unspecific nature of its clinical presentation may prevent correct diagnosis. The aim of the study was to assess the prevalence of ALPL mutations in adult patients treated in rheumatological outpatient facilities with evident musculoskeletal symptoms typical for HPP.

METHODS

Over a period of 10 years 9,522 patients were screened in the rheumatology outpatient clinic of the Hanusch hospital Vienna. Serum ALP levels ≤ 40 U/L were found in 524 patients. After screening for secondary causes, 73 patients were invited for clinical evaluation. Genetic testing was performed in 23 patients with suspected HPP. Logistic regression models with Firth penalisation were used to estimate the unadjusted and BMI-adjusted association of each clinical factor with HPP.

RESULTS

Mutations in the ALPL gene were observed in 57% of genetically screened patients. Arthralgia, fractures, and pain were the leading symptoms in individuals with ALPL mutation. Chondrocalcinosis (OR 29.12; 95% CI 2.02-1593.52) and dental disease (OR 8.33; 95% CI 0.93-143.40) were associated with ALPL mutation, independent of BMI. Onset of symptoms in patients with ALPL mutation was at 35.1 (14.3) years, with a mean duration from symptoms to diagnosis of 14.4 (8.1) years. Bone mineral density (BMD) and trabecular bone score (TBS) as well as bone turnover markers were not indicative for HPP or ALPL mutation.

CONCLUSION

HPP can mimic rheumatologic diseases. Thus, HPP should be considered as a possible diagnosis in adult patients presenting with musculoskeletal pain of unknown origin in rheumatology outpatient clinics. In patients with persistently low ALP serum levels and unclear musculoskeletal pain, HPP as the underlying cause has to be considered.

Bone turnover and mineral metabolism in adult patients with hypophosphatasia treated with asfotase alfa

There is limited understanding of how asfotase alfa affects mineral metabolism and bone turnover in adults with pediatric-onset hypophosphatasia. This study showed that adults with hypophosphatasia treated with asfotase alfa experienced significant changes in biochemical markers of bone and mineral metabolism, possibly reflecting enhanced bone remodeling of previously osteomalacic bone.

INTRODUCTION

Hypophosphatasia (HPP), due to a tissue nonspecific alkaline phosphatase (TNSALP) deficiency, can cause impaired bone mineralization and turnover. Although HPP may be treated with asfotase alfa, an enzyme replacement therapy, limited data are available on how treatment with asfotase alfa affects mineral metabolism and bone turnover in adults with HPP.

METHODS

ALP substrates, bone turnover and mineral metabolism markers, and bone mineral density (BMD) data from EmPATHY, a single-center, observational study of adults (≥ 18 years) with pediatric-onset HPP treated with asfotase alfa (NCT03418389), were collected during routine clinical care and analyzed from baseline through 24 months of treatment.

RESULTS

Data from 21 patients showed significantly increased ALP activity and reduced urine phosphoethanolamine (PEA)/creatinine (Cr) ratios after baseline through 24 months of asfotase alfa treatment. There were significant transient increases in parathyroid hormone 1-84 (PTH), osteocalcin, and procollagen type 1 N-propeptide (P1NP) levels at 3 and 6 months and in tartrate-resistant acid phosphatase 5b (TRAP5b) levels at 3 months, with a significant decrease in N-terminal telopeptide of type 1 collagen (NTX) levels at 24 months. Lumbar spine BMD T scores continuously increased during treatment.

CONCLUSION

Significant changes in bone turnover and mineral metabolism markers after asfotase alfa treatment suggest that treatment-mediated mineralization may enable remodeling and bone turnover on previously unmineralized surfaces. Urine PEA/Cr ratios may be a useful parameter in monitoring treatment during routine care.

[Rare bone disorders and respective treatments]

Delineating the genetic background and the underlying pathophysiology of rare skeletal dysplasias enables a broader understanding of these disorders as well as novel perspectives regarding differential diagnosis and targeted development of therapeutic approaches. Hypophosphatasia (HPP) due to genetically determined Alkaline Phosphatase deficiency exemplifies this development. While an enzyme replacement therapy could be established for severe HPP with the prevailing bone manifestation, the clinical impact of not immediately bone-related manifestations just being successively understood. Correspondingly, the elucidation of the pathophysiology underlying renal phosphate wasting expanded our knowledge regarding phosphate metabolism and bone health and facilitated the development of an anti-FGF-23 Antibody for targeted treatment of X‑linked Hypophosphatemia (XLH). Evolutions regarding the nosology of osteogenesis imperfecta (OI) along with the identification of further causative genes also detected in the context of genetically determined osteoporosis illustrate the pathophysiologic interrelation between monogenetic bone dysplasias and multifactorial osteoporosis. While current therapeutic strategies for OI follow osteoporosis treatment, the expanding knowledge about OI forms the fundament for establishing improved treatment strategies-for both OI and osteoporosis. Similar developments are emerging regarding rare skeletal disorders like Achondroplasia, Fibrodysplasia ossificans progressive and Morbus Morquio (Mukopolysaccharidosis Type IV).