Vitamin D is a pro-hormone characterized by an intricate metabolism and regulation. It is well known for its role in calcium and phosphate metabolism, and in bone health. However, several studies have assessed a huge number of extra-skeletal functions, ranging from cell proliferation in some oncogenic pathways to antioxidant and immunomodulatory functions. Vitamin D exerts its role by binding to VDRs (vitamin D receptors), which are located in many different tissues. Moreover, VDRs are able to bind hundreds of genomic loci, modulating the expression of various primary target genes. Interestingly, plenty of gene polymorphisms regarding VDRs are described, each one carrying a potential influence against gene expression, with relapses in several chronic diseases and metabolic complications. In this review, we provide an overview of the genetic aspects of vitamin D and VDR, emphasizing the gene regulation of vitamin D, and the genetic modulation of VDR target genes. In addition, we briefly summarize the rare genetic disease linked to vitamin D metabolism.

Purpose: This study investigates the role of CASR gene polymorphisms (A986S, R990G, Q1011E) in PHPT genetic susceptibility and its clinical variability. The aim is to evaluate the prevalence of these polymorphisms in patients with sporadic PHPT and their impact on clinical course, biochemistry, and histological features. Methods: 106 patients underwent clinical and anamnestic evaluations, focusing on major PHPT complications, as well as biochemical analyses of blood and urine. Genetic testing was conducted for CASR gene polymorphisms. Histological data were available for 68 patients who underwent parathyroidectomy. Results: The sample included 83 women and 23 men; mean age at diagnosis was 54.5 years. 55 patients carried CASR gene polymorphisms, while 51 were wild-type. Prevalence rates of polymorphisms were consistent with data for the Caucasian population, with A986S being the most common (31%). No significant associations were found between polymorphisms and increased levels of ionized calcium or other blood phospho-calcium metabolism parameters. However, 24-h urinary calcium levels were higher in patients with polymorphisms (p = 0.0185), particularly in those older than 50 years (p = 0.030) and with the A986S variant. Hypercalciuria was predictive of CASR polymorphism presence (OR = 2.76, p = 0.003). No significant association with PHPT complications, such as renal calculi or bone involvement, was confirmed. Histological data revealed no clear links between polymorphisms and more aggressive variants. Conclusions: CASR gene polymorphisms are associated with hypercalciuria but do not significantly influence age of onset or clinical phenotype in PHPT. Genetic analysis may be useful in selected cases to better understand individual clinical profiles.

Background/Objectives: X-linked hypophosphatemia (XLH), the most frequent heritable cause of hypophosphatemic rickets, is characterized by impaired linear growth and skeletal deformities, that can lead to disproportionate short stature. Linear growth depends on the coordinated regulation of systemic endocrine signals and local growth plate regulatory mechanisms controlling chondrocyte proliferation, differentiation, and apoptosis. This review critically discusses the molecular processes underlying growth impairment in XLH, with particular emphasis on growth plate dysfunction. Methods: A narrative review of experimental and clinical studies was conducted, focusing on growth plate biology, and on pathophysiology of XLH. Particular attention was given to the interaction between systemic phosphate-regulating hormones, local paracrine factors, and intracellular signaling pathways, as well as the effects of current therapeutic strategies on linear growth. Results: Excess fibroblast growth factor 23 (FGF23) in XLH disrupts phosphate homeostasis and vitamin D metabolism, impairing skeletal mineralization and growth plate signaling. Beyond FGF23-related dysregulation, additional FGF23-independent mechanisms directly affect growth plate chondrocyte function and extracellular matrix composition, further contributing to growth plate disorganization. Current therapeutic approaches, including conventional phosphate and active vitamin D supplementation, FGF23 inhibition with human monoclonal antibody, and combination with recombinant human growth hormone, exert heterogeneous effects on linear growth through distinct biological mechanisms. Conclusions: Growth impairment in XLH reflects the combined impact of alteration of calcium-phosphate metabolism, systemic endocrine dysregulation, and intrinsic growth plate dysfunctions. A better understanding of these mechanisms may facilitate the development of targeted therapeutic strategies, improving growth outcomes in individuals with XLH.

Background/Objectives: X-linked hypophosphatemia (XLH), the most frequent heritable cause of hypophosphatemic rickets, is characterized by impaired linear growth and skeletal deformities, that can lead to disproportionate short stature. Linear growth depends on the coordinated regulation of systemic endocrine signals and local growth plate regulatory mechanisms controlling chondrocyte proliferation, differentiation, and apoptosis. This review critically discusses the molecular processes underlying growth impairment in XLH, with particular emphasis on growth plate dysfunction. Methods: A narrative review of experimental and clinical studies was conducted, focusing on growth plate biology, and on the pathophysiology of XLH. Particular attention was given to the role of systemic phosphate-regulating hormones, local paracrine factors, and intracellular signaling pathways, as well as the effects of current therapeutic strategies on linear growth. Results: Excess fibroblast growth factor 23 (FGF23) in XLH disrupts phosphate homeostasis and vitamin D metabolism, impairing skeletal mineralization and growth plate signaling. Beyond FGF23-related dysregulation, additional FGF23-independent mechanisms directly affect growth plate chondrocyte function and extracellular matrix composition, further contributing to growth plate disorganization. Current therapeutic approaches, including conventional phosphate and active vitamin D supplementation, FGF23 inhibition with human monoclonal antibody, and combination with recombinant human growth hormone, exert heterogeneous effects on linear growth through distinct biological mechanisms. Conclusions: Growth impairment in XLH reflects the combined impact of systemic endocrine dysregulation, and intrinsic growth plate dysfunctions. A better understanding of these mechanisms may facilitate the development of targeted therapeutic strategies, improving growth outcomes in individuals with XLH.