Orphanet Journal of Rare Diseases | A Decade of Global Registry Insights into Hypophosphatasia

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This article summarizes a decade of global registry data on Hypophosphatasia (HPP), providing in-depth analysis on diagnostic delays, disease burden, genetic characteristics, and the efficacy of enzyme replacement therapy. The study highlights the multi-system manifestations of HPP and its implications for clinical diagnosis and therapeutic strategies.

 

Literature Overview

The article titled 'A Decade of Global Registry Insights into Hypophosphatasia' published in the Orphanet Journal of Rare Diseases reviews and summarizes key data collected over the past decade by the Global Hypophosphatasia Registry. It analyzes the age at diagnosis, ALP substrate testing, genetic profiles, non-skeletal manifestations, disease burden, and real-world efficacy of enzyme replacement therapy (asfotase alfa) in HPP patients. An updated classification system for HPP is also proposed, reflecting a more comprehensive understanding of its clinical continuum.

Background Information

Hypophosphatasia (HPP) is a rare metabolic genetic disorder caused by mutations in the ALPL gene, which leads to reduced activity of tissue-nonspecific alkaline phosphatase (ALP), resulting in impaired bone mineralization and a variety of non-skeletal manifestations. Clinical presentations of HPP are highly heterogeneous, ranging from fatal respiratory failure in infancy to rickets in childhood, fractures, and tooth loss in adulthood. Due to its rarity and clinical variability, HPP is often diagnosed with significant delay, especially in adults. Over the past decade, the Global HPP Registry has collected data from more than 1,500 patients, offering a valuable resource for studying the natural history, clinical features, genetic heterogeneity, and treatment responses in HPP. Currently, diagnosis of HPP relies on reduced ALP activity and ALPL mutation testing, but the use of ALP substrates such as PLP and PEA varies across regions, and standardized assessment criteria are lacking. The study also emphasizes that HPP is not only a skeletal disorder but a multi-system condition, with disease burden closely related to age at onset, number of genetic variants, and presence of non-skeletal symptoms. This article reviews major findings from the past decade of the HPP registry, proposes an updated classification system, and outlines directions for future research and therapeutic strategies.

 

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Study Methods and Experiments

The study leverages data from the Global Hypophosphatasia Registry to analyze age at diagnosis, ALP substrate testing rates, genetic variants, disease burden, and treatment outcomes in HPP patients. The research team also reviewed relevant literature and integrated registry data from the past decade to explore clinical heterogeneity, inheritance patterns, diagnostic delays, and their impact on quality of life. In addition, the study proposes a new HPP classification system, dividing HPP into early-onset (<6 months) and late-onset (≥6 months), and compares the clinical and genetic characteristics between these groups.

Key Findings and Insights

• Global registry data show two diagnostic peaks in early childhood and mid-adulthood, suggesting HPP can be recognized at multiple life stages.
• There is significant regional variation in the use of PLP and PEA testing, with the highest PLP testing rates in U.S. patients (61%) and the highest PEA testing rates in Japanese patients (48%).
• Approximately 75% of HPP patients are heterozygous carriers, and 25% are homozygous or compound heterozygous, indicating that HPP can result from a single mutant allele.
• Early-onset HPP patients (<6 months) often present with higher disease severity, including respiratory failure and vitamin B6-responsive seizures, and are typically compound heterozygotes.
• Across all age groups and mutation statuses, HPP patients commonly experience significant disease burden, including pain, mobility issues, fractures, and reduced quality of life.
• The proposed new classification system divides HPP into early-onset (<6 months) and late-onset(≥6 months), more accurately reflecting the clinical continuum of the disease.
• Asfotase alfa has shown sustained improvement in walking ability, bone density, and quality of life in real-world settings, although injection site reactions are common.
• The study emphasizes the need to further define diagnostic criteria for HPP, particularly in adults, and to explore the role of genetic modifiers in disease expression.

Implications and Future Directions

This study provides new insights into the diagnosis, classification, and treatment of HPP, highlighting the importance of non-skeletal manifestations in disease evaluation. Future research can leverage registry data to explore the natural history, long-term treatment outcomes, and genetic modifiers of HPP, while also optimizing genetic testing and biochemical assessments to improve early diagnosis. Moreover, the new classification system offers a more reliable framework for clinical management, research design, and patient stratification.

 

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Conclusion

In summary, the Global Hypophosphatasia Registry has significantly advanced our understanding of HPP over the past decade. The study reveals widespread diagnostic delays, especially in adult patients, and underscores the value of PLP and PEA testing in accurate diagnosis. HPP is no longer considered solely a skeletal disorder but a multi-system condition with highly variable clinical manifestations and disease burden. The new classification system helps clinicians better assess disease stage and treatment timing. Real-world evidence supports asfotase alfa as a first-line therapy. Future efforts will focus on long-term follow-up, treatment efficacy, and genetic studies using registry data to develop more precise therapeutic strategies. Additionally, further investigation into the impact of vitamin B6 intake and sample storage conditions on PLP testing, as well as standardization of PEA assessments, is needed to enhance diagnostic accuracy and consistency.

 

Priya S Kishnani, Lothar Seefried, Keiichi Ozono, Anna Petryk, and Kathryn M Dahir. The Global Hypophosphatasia Registry: lessons learned from a decade of real-world data. Orphanet Journal of Rare Diseases.