Investigation of ALPL variant states and clinical outcomes: An analysis of adults and adolescents with hypophosphatasia treated with asfotase alfa

EHMT2 as a Candidate Gene for an Autosomal Recessive Neurodevelopmental Syndrome

Neurodevelopmental disorders (NDD) comprise clinical conditions with high genetic heterogeneity and a notable enrichment of genes involved in regulating chromatin structure and function. The EHMT1/2 epigenetic complex plays a crucial role in repression of gene transcription in a highly tissue- and temporal-specific manner. Mutations resulting in heterozygous loss-of-function (LoF) of EHMT1 are implicated in Kleefstra syndrome 1 (KS1). EHMT2 is a gene acting in epigenetic regulation; however, the involvement of mutations in this gene in the etiology of NDDs has not been established thus far. A homozygous EHMT2 LoF variant [(NM_006709.5):c.328 + 2 T > G] was identified by exome sequencing in an adult female patient with a phenotype resembling KS1, presenting with intellectual disability, aggressive behavior, facial dysmorphisms, fused C2-C3 vertebrae, ventricular septal defect, supernumerary nipple, umbilical hernia, and fingers and toes abnormalities. The absence of homozygous LoF EHMT2 variants in population databases underscores the significant negative selection pressure exerted on these variants. In silico evaluation of the effect of the EHMT2(NM_006709.5):c.328 + 2 T > G variant predicted the abolishment of intron 3 splice donor site. However, manual inspection revealed potential cryptic donor splice sites at this EHMT2 region. To directly access the impact of this splice site variant, RNAseq analysis was employed and disclosed the usage of two cryptic donor sites within exon 3 in the patient's blood, which are predicted to result in either an out-of-frame or in-frame effect on the protein. Methylation analysis was conducted on DNA from blood samples using the clinically validated EpiSign assay, which revealed that the patient with the homozygous EHMT2(NM_006709.5):c.328 + 2 T > G splice site variant is conclusively positive for the KS1 episignature. Taken together, clinical, genetic, and epigenetic data pointed to a LoF mechanism for the EHMT2 splice variant and support this gene as a novel candidate for an autosomal recessive Kleefstra-like syndrome. The identification of additional cases with deleterious EHMT2 variants, alongside further functional validation studies, is required to substantiate EHMT2 as a novel NDD gene.

Diagnosis, treatment, and follow-up of patients with hypophosphatasia

INTRODUCTION

Hypophosphatasia is a rare inherited systemic metabolic disorder, with an estimated prevalence in the severe forms of the disease of 1/100.000-1/300.000, that affects the typical architecture of bone, leading to defective mineralization during growth and remodeling. It is characterized by loss-of-function variants in the ALPL gene, resulting in low activity of tissue-nonspecific alkaline phosphatase. In severe cases, it can be fatal.

OBJECTIVE

To generate recommendations on the diagnosis, treatment, and follow-up of patients with hypophosphatasia based on available evidence.

MATERIALS AND METHODS

A search for evidence published between 2012 and 2024 was carried out in Medline and Embase. The search was expanded with information from various sources, including official sites of development groups, consensuses, technology evaluations, Google Scholar, clinical experts, and reference lists. The quality of the evidence was evaluated according to the type of document type. A modified Delphi consensus process was carried out with external experts, apart from the development group, it was established an 80% agreement threshold to define the final recommendations.

RESULTS

Sixty-one papers were found in the evidence search. The global quality of the evidence was low. In addition, a consensus was reached on 94 recommendations regarding diagnosis, treatment, and follow-up. Those recommendations were approved by external clinical experts from Colombia, Argentina, Spain, and Mexico.

CONCLUSIONS

The recommendations proposed in this document are based on the evidence available to the date the search was carried out, and the judgment of clinical experts. The recommendations on diagnosis, treatment, and follow-up are expected to guide the daily clinical practice for patients with HPP.

Prenatal asfotase alfa-mediated enzyme replacement therapy restores delayed calcification in a severe infantile form of hypophosphatasia model mice

Hypophosphatasia (HPP) is a congenital disorder caused by mutations in the tissue-nonspecific alkaline phosphatase (TNALP) gene. The pathogenesis of HPP varies, ranging from severe cases in which there is total absence of fetal bone calcification, which leads to stillbirth, to relatively mild cases in which the effects are confined to the teeth, such as early loss of the primary teeth. In recent years, the establishment of enzyme supplementation as a treatment method has prolonged survival in patients; however, this approach does not provide sufficient improvement for failed calcification. Furthermore, the effects of enzyme replacement therapy on the jawbone and periodontal tissues have not yet been studied in detail. Therefore, in this study, we investigated the therapeutic effects of enzyme replacement therapy on jawbone hypocalcification in mice. Recombinant TNALP was administered to mothers before birth and newborns immediately after birth, and the effect of treatment was evaluated at 20 days of age. The treated HPP mice had improved mandible (mandibular length and bone quality) and tooth quality (root length of mandibular first molar, formation of cementum), as well as improved periodontal tissue structure (structure of periodontal ligament). Furthermore, prenatal treatment had an additional therapeutic effect on the degree of mandible and enamel calcification. These results suggest that enzyme replacement therapy is effective for the treatment of HPP, specifically in the maxillofacial region (including the teeth and mandible), and that early initiation of treatment may have additional beneficial therapeutic effects.

SARS-CoV-2 mRNA Dual Immunization Induces Innate Transcriptional Signatures, Establishes T-Cell Memory and Coordinates the Recall Response

BACKGROUND

mRNA vaccines have played a crucial role in controlling the SARS-CoV-2 global pandemic. However, the immunological mechanisms involved in the induction, magnitude and longevity of mRNA-vaccine-induced protective immunity are still unclear.

METHODS

In our study, we used whole-RNA sequencing along with detailed immunophenotyping of antigen-specific T cells and humoral RBD-specific response to dual immunization with the Pfizer-BioNTech mRNA vaccine (BNT162b2) and correlated them with response to an additional dose, administered 10 months later, in order to comprehensively profile the immune response of healthy volunteers to BNT162b2.

RESULTS

Primary dual immunization induced upregulation of the Type I interferon pathway and generated spike protein (S)-specific IFN-γ+ and TNF-α+ CD4 T cells, S-specific memory CD4 T cells, and RBD-specific antibodies against SARS-CoV-2. S-specific CD4 T cells induced by the primary series correlated with the RBD-specific antibody titers to a third dose.

CONCLUSIONS

This study demonstrates the induction of both innate and adaptive immunity in response to the BNT162b2 mRNA vaccine in a coordinated manner and identifies the central role of primarily induced CD4+ T cells as a predictive biomarker of the magnitude of anamnestic immune response.

Novel Therapeutic Agents for Rare Diseases of Calcium and Phosphate Metabolism

The last decade has been revolutionary regarding the management of rare bone diseases caused by impaired calcium and phosphate metabolism. Elucidation of the underlying genetic basis and pathophysiologic alterations has been the determinant factor for the development of new, disease-specific treatment agents. The phosphaturic hormone Fibroblast Growth Factor 23 (FGF23) possesses a critical role in the pathogenesis of various hypophosphatemic disorders. Among them, the genetic disorder of X-linked hypophosphatemia and the acquired syndrome of tumor-induced osteomalacia, although very rare, have attracted the scientific community's attention towards designing an FGF23-inhibitor as a potential specific therapy. The monoclonal antibody burosumab was approved for the treatment of children and adult patients with X-linked hypophosphatemia and recently for tumor-induced osteomalacia patients, demonstrating benefits regarding their symptoms, biochemical profile and bone mineralization status. Asfotase alfa is a hydroxyapatite-targeted recombinant alkaline phosphatase, an enzymatic replacement therapy, substituting the defective activity of tissue non-specific alkaline phosphatase, in patients suffering from hypophosphatasia. Promising data regarding its favorable effect on survival rate, bone quality, fracture healing, muscle strength, mobility, respiratory function, and general quality of life have led to the approval of the drug for the treatment of childhood-onset hypophosphatasia. Given the high costs of treatment for both agents and their limited clinical use until now, more data are needed to define patients' characteristics that make them ideal candidates for therapy. Long-term safety issues also need to be clarified.