Clinical and genetic characteristics of hypophosphatasia in Chinese children

Integrated Applied Clinical Pharmacology in the Advancement of Rare and Ultra-Rare Disease Therapeutics

The introduction of safe and effective rare/ultra-rare disease treatments is a focus of many biotherapeutic enterprises. Despite this increased activity, a significant unmet need remains, and the responsibility to meet this need is augmented by enhanced genomic, biologic, medical, analytical, and informatic tools. It is recognized that the development of an effective and safe rare/ultra-rare disease therapeutic faces a number of challenges with an important role noted for clinical pharmacology. Clinical pharmacology is foundationally an integrative discipline which must be embedded in and is interdependent upon understanding the pathogenic biology, clinical presentation, disease progression, and end-point assessment of the disease under study. This manuscript presents an overview and two case examples of this integrative approach, the development of C5-targeted therapeutics for the treatment of generalized myasthenia gravis and asfotase alpha for the treatment of hypophosphatasia. The two presented case examples show the usefulness of understanding the biological drivers and clinical course of a rare disease, having relevant animal models, procuring informative natural history data, importing assessment tools from relevant alternative areas, and using integrated applied clinical pharmacology to inform target engagement, dose, and the cascade of pharmacodynamic and clinical effects that follow. Learnings from these programs include the importance of assuring cross-validation of assays throughout a development program and continued commitment to understanding the relationship among the array of Pd end points and clinical outcomes. Using an integrative approach, substantive work remains to be done to meet the unmet needs of patients with rare/ultra-rare disease.

Catalyzing precision: unraveling the diagnostic conundrum of tunisian familial hypophosphatasia case through integrative clinical and molecular approaches

Familial Hypophosphatasia presents a complex diagnostic challenge due to its wide-ranging clinical manifestations and genetic heterogeneity. This study aims to elucidate the molecular underpinnings of familial Hypophosphatasia within a Tunisian family harboring a rare c.896 T > C mutation in the ALPL gene, offering insights into genotype-phenotype correlations and potential therapeutic avenues. The study employs a comprehensive approach, integrating biochemical examination, genetic analysis, structural modeling, and functional insights to unravel the impact of this rare mutation. Genetic investigation revealed the presence of the p.Leu299Pro mutation within the ALPL gene in affected family members. This mutation is strategically positioned in proximity to both the catalytic site and the metal-binding domain, suggesting potential functional consequences. Homology modeling techniques were employed to predict the 3D structure of TNSALP, providing insights into the structural context of the mutation. Our findings suggest that the mutation may induce conformational changes in the vicinity of the catalytic site and metal-binding domain, potentially affecting substrate recognition and catalytic efficiency. Molecular dynamics simulations were instrumental in elucidating the dynamic behavior of the tissue-nonspecific alkaline phosphatase isozyme (TNSALP) in the presence of the p.Leu299Pro mutation. The simulations indicated alterations in structural flexibility near the mutation site, with potential ramifications for the enzyme's overall stability and function. These dynamic changes may influence the catalytic efficiency of TNSALP, shedding light on the molecular underpinnings of the observed clinical manifestations within the Tunisian family. The clinical presentation of affected individuals highlighted significant phenotypic heterogeneity, underscoring the complex genotype-phenotype correlations in familial Hypophosphatasia. Variability in age of onset, severity of symptoms, and radiographic features was observed, emphasizing the need for a nuanced understanding of the clinical spectrum associated with the p.Leu299Pro mutation. This study advances our understanding of familial Hypophosphatasia by delineating the molecular consequences of the p.Leu299Pro mutation in the ALPL gene. By integrating genetic, structural, and clinical analyses, we provide insights into disease pathogenesis and lay the groundwork for personalized therapeutic strategies tailored to specific genetic profiles. Our findings underscore the importance of comprehensive genetic and clinical evaluation in guiding precision medicine approaches for familial Hypophosphatasia.

Clinical and Genetic Characteristics of Hypophosphatasia in Chinese Adults

Hypophosphatasia (HPP) is an inherited disease caused by ALPL mutation, resulting in decreased alkaline phosphatase (ALP) activity and damage to bone and tooth mineralization. The clinical symptoms of adult HPP are variable, making diagnosis challenging. This study aims to clarify the clinical and genetic characteristics of HPP in Chinese adults. There were 19 patients, including 1 with childhood-onset and 18 with adult-onset HPP. The median age was 62 (32-74) years and 16 female patients were involved. Common symptoms included musculoskeletal symptoms (12/19), dental problems (8/19), fractures (7/19), and fatigue (6/19). Nine patients (47.4%) were misdiagnosed with osteoporosis and six received anti-resorptive treatment. The average serum ALP level was 29.1 (14-53) U/L and 94.7% (18/19) of patients had ALP levels below 40 U/L. Genetic analysis found 14 ALPL mutations, including three novel mutations-c.511C>G (p.His171Ala), c.782C>A (p.Pro261Gln), and 1399A>G (p.Met467Val). The symptoms of two patients with compound heterozygous mutations were more severe than those with heterozygous mutations. Our study summarized the clinical characteristics of adult HPP patients in the Chinese population, expanded the spectrum of pathogenic mutations, and deepened clinicians' understanding of this neglected disease.

The impact of enzyme replacement therapy on the oral health manifestations of hypophosphatasia among children: a scoping review

PURPOSE

A scoping review to describe the use of enzyme replacement therapy (ERT) in the form of asfotase alfa to decrease the severity of oral manifestations in children with hypophosphatasia (HPP).

METHODS

Six databases were searched using keywords and index terms related to "hypophosphatasia," "children," and "enzyme replacement therapy." Duplicates were removed and two independent reviewers screened the titles and abstracts to identify articles for full-text review. Extracted data was summarised narratively.

RESULTS

The systematic search identified 3548 articles, with 171 suitable for full-text review and a final 22 that met inclusion criteria. Enzyme replacement therapy generally resulted in a reduction in the presence and severity of oral manifestations of HPP. However, numerous studies failed to report specific details regarding the nature of oral health outcomes and there were reported cases of further loss of primary teeth.

CONCLUSIONS

The available evidence suggests that that ERT in the form of asfotase alfa for HPP in infants and young children leads to improved oral health outcomes. It is recommended that the outcomes are improved with earlier initiation of ERT. Further, well-designed clinical research is required to assess oral health improvements and decreased morbidity associated with the early loss of teeth.

Clinical and Genetic Characteristics of Pediatric Patients with Hypophosphatasia in the Russian Population

(1) Hypophosphatasia (HPP) is a rare inherited disease caused by mutations (pathogenic variants) in the ALPL gene which encodes tissue-nonspecific alkaline phosphatase (TNSALP). HPP is characterized by impaired bone mineral metabolism due to the low enzymatic activity of TNSALP. Knowledge about the structure of the gene and the features and functions of various ALPL gene variants, taking into account population specificity, gives an understanding of the hereditary nature of the disease, and contributes to the diagnosis, prevention, and treatment of the disease. The purpose of the study was to describe the spectrum and analyze the functional features of the ALPL gene variants, considering various HPP subtypes and clinical symptoms in Russian children. (2) From 2014−2021, the study included the blood samples obtained from 1612 patients with reduced alkaline phosphatase activity. The patients underwent an examination with an assessment of their clinical symptoms and biochemical levels of TNSALP. DNA was isolated from dried blood spots (DBSs) or blood from the patients to search for mutations in the exons of the ALPL gene using Sanger sequencing. The PCR products were sequenced using a reagent BigDye Terminator 3.1 kit (Applied Biosystems). Statistical analysis was performed using the GraphPad Prism 8.01 software. (3) The most common clinical symptoms in Russian patients with HPP and two of its variants (n = 22) were bone disorders (75%), hypomyotonia (50%), and respiratory failure (50%). The heterozygous carriage of the causal variants of the ALPL gene was detected in 225 patients. A total of 2 variants were found in 27 patients. In this group (n = 27), we identified 28 unique variants of the ALPL gene, of which 75.0% were missense, 17.9% were frameshift, 3.6% were splicing variants, and 3.6% were duplications. A total of 39.3% (11/28) of the variants were pathogenic, with two variants being probably pathogenic, and 15 variants had unknown clinical significance (VUS). Among the VUS group, 28.6% of the variants (7/28) were discovered by us for the first time. The most common variants were c.571G > A (p.Glu191Lys) and c.1171del (Arg391Valfs*12), with frequencies of 48.2% (13/28) and 11% (3/28), respectively. It was found that the frequency of nonsense variants of the ALPL gene was higher (p < 0.0001) in patients with the perinatal form compared to the infantile and childhood forms of HPP. Additionally, the number of homozygotes in patients with the perinatal form exceeded (p < 0.01) the frequencies of these genotypes in children with infantile and childhood forms of HPP. On the contrary, the frequencies of the compound-heterozygous and heterozygous genotypes were higher (p < 0.01) in patients with infantile childhood HPP than in perinatal HPP. In the perinatal form, residual TNSALP activity was lower (p < 0.0005) in comparison to the infantile and childhood (p < 0.05) forms of HPP. At the same time, patients with the heterozygous and compound-heterozygous genotypes (mainly missense variants) of the ALPL gene had greater residual activity (of the TNSALP protein) regarding those homozygous patients who were carriers of the nonsense variants (deletions and duplications) of the ALPL gene. Residual TNSALP activity was lower (p < 0.0001) in patients with pathogenic variants encoding the amino acids from the active site and the calcium and crown domains in comparison with the nonspecific region of the protein.