Hereditary Hypercalcemia Caused by a Homozygous Pathogenic Variant in the CYP24A1 Gene: A Case Report and Review of the Literature

Infantile hypercalcemia type 1 (HCINF1): a rare disease resulting in nephrolithiasis and nephrocalcinosis caused by mutations in the vitamin D catabolic enzyme, CYP24A1

Infantile hypercalcemia type 1 (HCINF1), formerly known as Lightwood syndrome, is a subtype of hypercalcemia caused by loss-of-function biallelic mutations in the vitamin D catabolic enzyme, CYP24A1, which 24-hydroxylates the hormone 1,25-(OH)2D3. This short review focuses on the main features of the HCINF1 disease; emerging knowledge of the structure and function of the cytochrome P450, CYP24A1 and the location of inactivating mutations; the development of a rapid LC-MS/MS-based laboratory test for defective 24-hydroxylation; and future implications for bioanalytical assay and treatment of all types of vitamin D-related hypercalcemic conditions.

Persistent hypercalcaemia associated with two pathogenic variants in the CYP24A1 gene and a parathyroid adenoma-a case report and review

Introduction

24-Hydroxylase, encoded by the CYP24A1 gene, is a crucial enzyme involved in the catabolism of vitamin D. Loss-of-function mutations in CYP24A1 result in PTH-independent hypercalcaemia with high levels of 1,25(OH)2D3. The variety of clinical manifestations depends on age, and underlying genetic predisposition mutations can lead to fatal infantile hypercalcaemia among neonates, whereas adult symptoms are usually mild.

Aim of the study

We report a rare case of an adult with primary hyperparathyroidism and loss-of-function mutations in the CYP24A1 gene and a review of similar cases.

Case presentation

We report the case of a 58-year-old woman diagnosed initially with primary hyperparathyroidism. Preoperatively, the suspected mass adjoining the upper pole of the left lobe of the thyroid gland was found via ultrasonography and confirmed by 99mTc scintigraphy and biopsy as the parathyroid gland. The patient underwent parathyroidectomy (a histopathology report revealed parathyroid adenoma), which led to normocalcaemia. After 10 months, vitamin D supplementation was introduced due to deficiency, and the calcium level remained within the reference range. Two years later, biochemical tests showed recurrence of hypercalcaemia with suppressed parathyroid hormone levels and elevated 1,25(OH)2D3 concentrations. Further investigation excluded the most common causes of PTH-independent hypercalcaemia, such as granulomatous disease, malignancy, and vitamin D intoxication. Subsequently, vitamin D metabolites were measured using LC-MS/MS, which revealed high levels of 25(OH)D3, low levels of 24,25(OH)2D3 and elevated 25(OH)2D3/24,25(OH)2D3 ratios, suggesting a defect in vitamin D catabolism. Molecular analysis of the CYP24A1 gene using the NGS technique revealed two pathogenic variants: p.(Arg396Trp) and p.(Glu143del) (rs114368325 and rs777676129, respectively).

Conclusions

The diagnostic process for hypercalcaemia becomes complicated when multiple causes of hypercalcaemia coexist. The measurement of vitamin D metabolites using LC-MS/MS may help to identify carriers of CYP24A1 mutations. Subsequent molecular testing may contribute to establishing the exact frequency of pathogenic variants of the CYP24A1 gene and introducing personalized treatment.

When to suspect infantile hypercalcemia-1?

PURPOSE

The screening test to suspect infantile hypercalcemia-1 (HCINF1) is the measure of 25(OH)D3/24,25(OH)2D3 ratio at mass spectroscopy (MS). When the ratio is > 80, the gold standard for the diagnosis is genetic analysis. Given its limited availability, MS may not represent a screening test and most cases of HCINF1 remain undiagnosed. Aim of the study is to identify cut-offs of serum calcium and PTH useful to suspect patients with HCINF1.

METHODS

We compared the levels of total serum calcium and PTH of 6 patients with HCINF1 harboring biallelic CYP24A1 pathogenic variants with 3 different control groups: (1) 12 subjects wild type for CYP24A1; (2) 12 subjects matched for age and sex; (3) 12 subjects matched for vitamin D levels. We validated the cut-offs, testing the number of adult patients affected by HCINF1 reported in the literature that could be identified using these cut-offs.

RESULTS

A serum calcium level > 9.6 mg/dL showed the highest sensitivity (100%) and specificity (91%) in the comparison between homozygous and wild-type subjects. A serum PTH index < 0.315 showed the highest sensitivity (100%) and specificity (83.3%). A serum calcium level > 9.6 mg/dL was able to identify all adult HCINF1 patients whereas a PTH ratio < 0.315 identified 89.8% of the cases. Superimposable results were obtained using the other control groups.

CONCLUSION

Patients with serum calcium levels higher than 9.6 mg/dL and a PTH index lower than 0.315 are likely to be affected by HCINF1. Their diagnosis may be confirmed using MS and genetic analysis.

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.

Case report: Two heterozygous pathogenic variants of CYP24A1: A novel cause of hypercalcemia and nephrocalcinosis in adulthood

Background and aims

Vitamin D 24-hydroxylase is an enzyme encoded by the CYP24A1 gene, which inhibits the activation of vitamin D to form inactive metabolites. More than 20 currently described pathogenic variants (usually biallelic) of this gene are responsible for idiopathic infantile hypercalcemia manifested typically in childhood (often in newborns) with hypercalcemia, hypercalciuria, and nephrocalcinosis. However, a few patients (mostly with monoallelic heterozygous pathogenic variants) can develop mild symptoms in adulthood.

Case description

We present the case of a 43-year-old male patient with hypertension and heterozygous Leiden mutation, with mural thrombi in the common iliac artery, who was sent by a nephrologist to endocrinological examination due to hypoparathyroidism, progressive hypercalcemia, hypercalciuria, and CKDG2A1. Complete laboratory and imaging methods (including PET-CT) excluded PTH-related peptide-mediated hypercalcemia and granulomatosis. Finally, the genetic analysis of the CYP24A1 gene revealed the presence of a novel combination of two heterozygous pathogenic variants: CYP24A1: c. 443T>C p.(Leu148Pro) and c.1186C>T p.(Arg396Trp).

Conclusion

Differential diagnosis of patients with hypercalciuria, nephrocalcinosis, and hypercalcemia related to vitamin D exposure should include the CYP24A1 gene mutation. To the best of our knowledge, this is the first case of the novel combination of two heterozygous pathogenic variants of CYP24A1.

CYP24A1 and SLC34A1 Pathogenic Variants Are Uncommon in a Canadian Cohort of Children with Hypercalcemia or Hypercalciuria

OBJECTIVES

Biallelic pathogenic variants in CYPA24A1 and SLC34A1 are causes of idiopathic infantile hypercalcemia. Pathogenic variants in both may also give rise to hypercalciuria with nephrocalcinosis or nephrolithiasis without previous hypercalcemia (renal group). Our objective was to examine the frequency of CYP24A1 or SLC34A1 variants in children with early hypercalcemia or late-onset hypercalciuria.

METHOD

Forty-one children from 7 centers across Canada were recruited. Local investigations were undertaken. The serum was evaluated by liquid chromatography tandem-mass spectrometry for the ratio of 25-hydroxyvitamin D3 to 24,25-dihydroxyvitamin D3, (25-OH-D3:24,25-(OH)2D3), an elevation pathognomonic for the loss of function of the CYP24A1 enzyme. Mutational analyses were undertaken. Family cascade screening was performed if pathogenic variants were detected in probands.

RESULTS

Twenty-nine children had early-onset hypercalcemia; none had elevated 25-OH-D3:24,25-(OH)2D3 or variants. Interestingly, 2 of 12 in the renal group had elevated 25-OH-D3:24,25-(OH)2D3 and presented as preadolescents. In case 1, cascade testing revealed a sibling and parent with asymptomatic pathogenic variants in CYP24A1. Four CYP24A1 pathogenic variants were identified in these 2 probands: 3 have been described in European populations, and 1 is a rare variant in exon 7 (c931delC) that is likely pathogenic. No SLC34A1 pathogenic variants were detected.

CONCLUSION

In Canada, pathogenic variants in CYP24A1 appear to manifest with late-onset hypercalciuria and its sequelae. The 25-OH-D3:24,25-(OH)2D3 ratio is an excellent tool for screening for biallelic pathogenic variants in CYP24A1. We confirm that cascade testing is important for these variants.

Duplex high resolution melting analysis (dHRMA) to detect two hot spot CYP24A1 pathogenic variants (PVs) associated to idiopathic infantile hypercalcemia (IIH)

Pathogenic variants (PVs) in CYP24A1 gene are associated with Idiopathic Infantile Hypercalcemia disease (IIH). The identification of CYP24A1 PVs can be a useful tool for the improvement of target therapeutic strategies. Aim of this study is to set up a rapid and inexpensive High Resolution Melting Analysis (HRMA)-based method for the simultaneous genotyping of two hot spot PVs in CYP24A1 gene, involved in IIH. A duplex-HRMA (dHRMA) was designed in order to detect simultaneously CYP24A1 c.428_430delAAG, p.(Glu143del) (rs777676129) and c.1186C > T, p.(Arg396Trp) (rs114368325), in peculiar cases addressed to our Laboratory. dHRMA was able to identify clearly and simultaneously both hot spot CYP24A1 PVs evaluating melting curve shape and melting temperature (T_m). This is the first dHRMA approach to rapidly screen the two most frequent CYP24A1 PVs in peculiar case, providing useful information for diagnosis and patient management in IIH disease.

An Update on Vitamin D Metabolism

Vitamin D is a steroid hormone classically involved in the calcium metabolism and bone homeostasis. Recently, new and interesting aspects of vitamin D metabolism has been elucidated, namely the special role of the skin, the metabolic control of liver hydroxylase CYP2R1, the specificity of 1α-hydroxylase in different tissues and cell types and the genomic, non-genomic and epigenomic effects of vitamin D receptor, which will be addressed in the present review. Moreover, in the last decades, several extraskeletal effects which can be attributed to vitamin D have been shown. These beneficial effects will be here summarized, focusing on the immune system and cardiovascular system.

Biallelic CYP24A1 variants presenting during pregnancy: clinical and biochemical phenotypes

INTRODUCTION

Inactivating mutations in CYP24A1, encoding vitamin D-24-hydroxylase, can lead to an accumulation of active vitamin D metabolites and consequent hypercalcaemia. Patient (infantile and adult) presentation is varied and includes mild-severe hypercalcaemia, hypercalciuria, nephrocalcinosis and nephrolithiasis. This study aimed to characterize the clinical and biochemical phenotypes of a family with two CYP24A1 missense variants.

METHODS

The proband and seven family members underwent detailed clinical and biochemical evaluation. Laboratory measurements included serum calcium, intact parathyroid hormone (iPTH), vitamin D metabolites and urine calcium and creatinine.

RESULTS

The proband presented during the second trimester of a planned pregnancy with flu-like symptoms. Laboratory tests showed elevated adjusted calcium of 3.27 (upper reference limit (URL: 2.30) mmol/L), suppressed iPTH (<6 ng/L), elevated 25(OH)D (264 (URL: 55) nmol/L) and elevated 1,25(OH)D (293 (URL: <280) pmol/L). Ionized calcium was 1.55 (URL: 1.28) mmol/L. Sanger sequencing revealed two heterozygous missense variants in the CYP24A1: p.(Arg439Cys), R439C and p.(Trp275Arg), W275R. The proband's brother and sister had the same genotype. The brother had intermittent hypercalcaemia and hypervitaminosis D. Only the sister had a history of nephrolithiasis. The proband's daughter and two nephews were heterozygous for the R439C variant. The proband and her brother frequently had elevated 25(OH)D:24,25(OH)2D ratios (>50) during follow-up.

CONCLUSIONS

W275R is a new pathogenic CYP24A1 mutation in compound heterozygotic form with R439C in this family.

Consensus statement from 2nd International Conference on Controversies in Vitamin D

The 2nd International Conference on Controversies in Vitamin D was held in Monteriggioni (Siena), Italy, September 11-14, 2018. The aim of this meeting was to address ongoing controversies and timely topics in vitamin D research, to review available data related to these topics and controversies, to promote discussion to help resolve lingering issues and ultimately to suggest a research agenda to clarify areas of uncertainty. Several issues from the first conference, held in 2017, were revisited, such as assays used to determine serum 25-hydroxyvitamin D [25(OH)D] concentration, which remains a critical and controversial issue for defining vitamin D status. Definitions of vitamin D nutritional status (i.e. sufficiency, insufficiency and deficiency) were also revisited. New areas were reviewed, including vitamin D threshold values and how they should be defined in the context of specific diseases, sources of vitamin D and risk factors associated with vitamin D deficiency. Non-skeletal aspects related to vitamin D were also discussed, including the reproductive system, neurology, chronic kidney disease and falls. The therapeutic role of vitamin D and findings from recent clinical trials were also addressed. The topics were considered by 3 focus groups and divided into three main areas: 1) "Laboratory": assays and threshold values to define vitamin D status; 2) "Clinical": sources of vitamin D and risk factors and role of vitamin D in non-skeletal disease and 3) "Therapeutics": controversial issues on observational studies and recent randomized controlled trials. In this report, we present a summary of our findings.

The association analysis between CYP24A1 genetic polymorphisms and the risk of ischemic stroke in Chinese Han population

AIMS

Stroke is a complicated neurological disease and the second leading cause of death in the world. We aimed to investigate the association between CYP24A1 genetic polymorphisms and ischemic stroke risk.

METHODS

In this case-control study, four single-nucleotide polymorphisms of CYP24A1 were selected and genotyped by MassARRAY platform in Chinese Han population. Odds ratios and 95% confidence intervals were calculated via logistic regression analysis with adjustment in genetic models.

RESULTS

Our results indicated that CYP24A1 variant (rs1570669) was associated with the decreased risk of ischemic stroke (OR = 0.60, p < .001). Stratification analysis showed that the rs6068816 could enhance the ischemic stroke risk by 1.64 times (OR = 1.64, p = .028), while rs1570669 played protective role (OR = 0.63, p = .044) in age >64 years. The rs2762934 had an increased ischemic stroke susceptibility (OR = 1.62, p = .033); however, rs1570669 might reduce stroke risk (OR = 0.61, p = .015) in age ≤64 years. The rs1570669 depressed ischemic stroke susceptibility both in female and male patients (OR = 0.46, p = .002; OR = 0.69, p = .033, respectively), and rs2296241 would weaken the risk in male (OR = 0.63, p = .012). The rs1570669 was associated with decreased risk of ischemic stroke with hypertension (OR = 0.56, p = .042).

CONCLUSION

Our study gave the evidences that CYP24A1 genetic polymorphisms were significantly associated with ischemic stroke patients, which would provide useful information of assessment or possible diagnostic markers for ischemic stroke.