24-Hydroxylase Deficiency Due to CYP24A1 Sequence Variants: Comparison With Other Vitamin D-mediated Hypercalcemia Disorders

Clinical heterogeneity and therapeutic options for idiopathic infantile hypercalcemia caused by CYP24A1 pathogenic variant

OBJECTIVES

Infantile hypercalcemia-1 (HCINF1) is a rare disease caused by pathogenic variants in the CYP24A1 gene, resulting in the inability to metabolize active vitamin D. This leads to hypercalcemia and severe complications.

CONTENT

On December 8th, 2022, a systematic literature search was conducted in PubMed, Wanfang, and CNKI using the keywords "hypercalcemia" and "CYP24A1". Data extraction included patient demographics, clinical presentation, treatment medications, and outcomes. The findings were synthesized to identify common patterns and variations among cases and to assess the efficacy of different therapies in reducing serum calcium. Our findings revealed two distinct peaks in the incidence of HCINF1 caused by CYP24A1 pathogenic variant. Kidney stones or renal calcifications were the most common clinical manifestations of the disease, followed by polyuria and developmental delay. Laboratory investigations showed hypercalcemia, elevated vitamin D levels, hypercalciuria, and low parathyroid hormone. Genetic analysis remains the only reliable diagnostic tool. Although there is no definitive cure for HCINF1, multiple drugs, including bisphosphonates, calcitonin, and rifampicin, have been used to control its symptoms. Blocking the production and intake of vitamin D is the preferred treatment option.

SUMMARY AND OUTLOOK

Our review highlights the basic clinical and biochemical features of HCINF1 and suggests that targeted diagnostic and therapeutic strategies are needed to address the clinical heterogeneity of the disease. The insights gained from this study may facilitate the development of innovative treatments for HCINF1.

Impaired Vitamin D Metabolism in Hospitalized COVID-19 Patients

There is increasing data regarding the association between vitamin D and COVID-19. This study aimed to reveal the alterations of vitamin D metabolism in the setting of COVID-19. We examined 119 adult COVID-19 inpatients and 44 apparently healthy adult individuals with similar serum 25OH-D3 levels as a reference group. The assessment included serum biochemical parameters (total calcium, albumin, phosphorus, creatinine), parathyroid hormone (PTH), vitamin D-binding protein (DBP), vitamin D metabolites (25OH-D3, 25OH-D2, 1,25(OH)2D3, 3-epi-25OH-D3, 24,25(OH)2D3 and D3) and free 25OH-D. COVID-19 patients had in general very low vitamin D levels (median 25OH-D3 equals 10.8 ng/mL), accompanied by an increased production of the active vitamin D metabolite (1,25(OH)2D3), estimated as higher 1,25(OH)2D3 serum levels (61 [44; 81] vs. 40 [35; 50] pg/mL, p < 0.001) and lower 25OH-D3/1,25(OH)2D3 ratio (175 [112; 260] vs. 272 [200; 433], p < 0.001) which is presumably aimed at preventing hypocalcemia. Patients with COVID-19 also had elevated DBP (450 [386; 515] vs. 392 [311; 433] mg/L, p < 0.001) and low free 25OH-D levels (<LoB vs. 3.9 [3.2; 4.4] pg/mL, p < 0.001). Follow-up assessment of the COVID-19 inpatients showed recovery of the observed changes. Overall, hospitalized patients with an acute course of COVID-19 have not only very low levels of 25OH-D but also profound abnormalities in the metabolism of vitamin D regardless of the clinical course of the disease. These alterations might exacerbate existing vitamin D deficiency and its negative impact.

Rapidly Increasing Serum 25(OH)D Boosts the Immune System, against Infections-Sepsis and COVID-19

Vitamin D deficiency is a global public health problem, a pandemic that commonly affects the elderly and those with comorbidities such as obesity, diabetes, hypertension, respiratory disorders, recurrent infections, immune deficiency, and malignancies, as well as ethnic minorities living in temperate countries. The same groups were worst affected by COVID-19. Since vitamin D deficiency weakens the immune system, it increases the risk of infections, complications, and deaths, such as from sepsis and COVID-19. Deficiency can be remedied cost-effectively through targeted food fortification, supplementation, and/or daily safe sun exposure. Its endocrine functions are limited to mineral metabolism, musculoskeletal systems, specific cell membrane interactions, and parathyroid gland functions. Except for the rapid, endocrine, and cell membrane-based non-genomic functions, all other biological and physiological activities of vitamin D depend on the adequate intracellular synthesis of 1,25(OH)2D (calcitriol) in peripheral target cells via the genome. Calcitriol mediates autocrine (intracrine) and paracrine signalling in immune cells, which provides broader, protective immune functions crucial to overcoming infections. The synthesis of 1,25(OH)2D (calcitriol) in peripheral target cells is dependent on diffusion and endocytosis of D3 and 25(OH)D from the circulation into them, which requires maintenance of serum 25(OH)D concentration above 50 ng/mL. Therefore, in acute infections such as sepsis and respiratory infections like COVID-19, it is necessary to rapidly provide its precursors, D3 and 25(OH)D, through the circulation to generate adequate intracellular calcitriol. Immune defence is one of the crucial non-hormonal functions of vitamin D. A single oral (bolus) dose or divided upfront loading doses between 100,000 and 500,000 IU, using 50,000 IU vitamin D3 increase the serum 25(OH)D concentrations to a therapeutic level of above 50 ng/mL that lasts between two to three months. This takes three to five days to raise serum 25(OH)D. In contrast, a single oral dose of calcifediol (0.014 mg/kg body weight) can generate the needed 25(OH)D concentration within four hours. Considering both D3 and 25(OH)D enter immune cells for generating calcitriol, using the combination of D3 (medium-term) and calcifediol (immediate) is cost-effective and leads to the best clinical outcome. To maximise protection against infections, particularly to reduce COVID-19-associated complications and deaths, healthcare workers should advise patients on safe sun exposure, adequate vitamin D supplementation and balanced diets containing zinc, magnesium, and other micronutrients to support the immune system. Meanwhile, governments, the World Health Organisation, the Centers for Disease Control, and governments should consider similar recommendations to physicians and the public, change the outdated vitamin D and other micronutrient recommendations directed to their population, and organise targetted food fortification programs for the vulnerable groups. This article discusses a rational approach to maintaining a sustained serum 25(OH)D concentration above 50 ng/mL, necessary to attain a robust immune system for overcoming infections. Such would cost-effectively improve the population’s health and reduce healthcare costs. It also describes three cost-effective, straightforward protocols for achieving and sustaining therapeutic serum 25(OH)D concentrations above 50 ng/mL (>125 nmol/L) to keep the population healthy, reduce absenteeism, improve productivity, and lower healthcare costs.