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Identification of hypophosphatasia in adults with persistent hypophosphatasemia: clinical-genetic characterization
Yazhao Mei1, Ziyuan Wang1, Na Ren1
1Shanghai Clinical Research Center of Bone Disease, Department of Osteoporosis and Bone Diseases, Shanghai Sixth People's Hospital Affiliated to Shanghai Jiao Tong University School of Medicine, Shanghai, China.
Abstract:
This study systematically analyzed 72 adults with genetically confirmed hypophosphatasia and compared them with 36 individuals with persistent hypophosphatasemia but negative ALPL variants. Using four routinely available indicators, a simplified diagnostic tool was developed and externally validated to facilitate the early identification of adult hypophosphatasia in clinical practice.
Purpose:
Hypophosphatasia (HPP), an underdiagnosed inborn error of disorder caused by ALPL mutations, poses diagnostic challenges in adults due to phenotypic heterogeneity. This study aimed to establish a large adult HPP cohort in China and develop a practical diagnostic tool using routine clinical parameters.
Methods:
Clinical and genetic characteristics were systematically analyzed in 72 genetically confirmed adult HPP patients and 36 individuals with persistent hypophosphatasemia and negative ALPL genetic testing. Two models were developed to predict HPP: Model 0 (alkaline phosphatase (ALP)+pyridoxal-5'-phosphate (PLP)) and Model 1 (ALP+height Z-score+family history+chronic musculoskeletal pain). Model performance was evaluated by tenfold cross-validation, decision curve analysis (DCA) and external validation (n = 40, including 28 HPP).
Results:
HPP patients exhibited lower ALP (27.0 (21.8, 33.3) U/L vs. 36.00 (32.0, 38.0) U/L; P < 0.001), elevated PLP (214.3 (121.3, 457.7) nmol/L vs. 42.6 (31.9, 63.5) nmol/L; P < 0.001), growth impairment, and higher prevalence of chronic musculoskeletal pain and family history. Optimal ALP and PLP cutoffs were 28.2 U/L and 114.9 nmol/L, respectively. Compound heterozygotes and crown domain variants in ALPL gene showed lower ALP and higher PLP levels. Model 1 performed comparably to Model 0 (AUC 0.918 vs. 0.896; P = 0.513), remained robust in the age-stratified sensitivity analysis (<50 years), and achieved an AUC of 0.833 in external validation. A nomogram based on Model 1 was constructed.
Conclusion:
This study provides the largest clinical-genetic characterization of adult HPP in China and proposes a simple four-variable nomogram that enables accurate recognition of HPP without PLP testing, facilitating earlier diagnosis in routine practice.
