Primary hyperparathyroidism in a patient with familial hypocalciuric hypercalcaemia due to a novel mutation in the calcium-sensing receptor gene

Prevalence and characteristics of genetic disease in adult kidney stone formers

BACKGROUND

Molecular mechanisms of kidney stone formation remain unknown in most patients. Previous studies have shown a high heritability of nephrolithiasis, but data on the prevalence and characteristics of genetic disease in unselected adults with nephrolithiasis are lacking. This study was conducted to fill this important knowledge gap.

METHODS

We performed whole exome sequencing in 787 participants in the Bern Kidney Stone Registry, an unselected cohort of adults with one or more past kidney stone episodes [kidney stone formers (KSFs)] and 114 non-kidney stone formers (NKSFs). An exome-based panel of 34 established nephrolithiasis genes was analysed and variants assessed according to American College of Medical Genetics and Genomics criteria. Pathogenic (P) or likely pathogenic (LP) variants were considered diagnostic.

RESULTS

The mean age of KSFs was 47 ± 15 years and 18% were first-time KSFs. A Mendelian kidney stone disease was present in 2.9% (23/787) of KSFs. The most common genetic diagnoses were cystinuria (SLC3A1, SLC7A9; n = 13), vitamin D-24 hydroxylase deficiency (CYP24A1; n = 5) and primary hyperoxaluria (AGXT, GRHPR, HOGA1; n = 3). Of the KSFs, 8.1% (64/787) were monoallelic for LP/P variants predisposing to nephrolithiasis, most frequently in SLC34A1/A3 or SLC9A3R1 (n = 37), CLDN16 (n = 8) and CYP24A1 (n = 8). KSFs with Mendelian disease had a lower age at the first stone event (30 ± 14 versus 36 ± 14 years; P = .003), were more likely to have cystine stones (23.4% versus 1.4%) and less likely to have calcium oxalate monohydrates stones (31.9% versus 52.5%) compared with KSFs without a genetic diagnosis. The phenotype of KSFs with variants predisposing to nephrolithiasis was subtle and showed significant overlap with KSFs without diagnostic variants. In NKSFs, no Mendelian disease was detected and LP/P variants were significantly less prevalent compared with KSFs (1.8% versus 8.1%).

CONCLUSION

Mendelian disease is uncommon in unselected adult KSFs, yet variants predisposing to nephrolithiasis are significantly enriched in adult KSFs.

Coexistence of a Calcium-Sensing Receptor Mutation and Primary Hyperparathyroidism

Primary hyperparathyroidism (PHPT) and familial hypocalciuric hypercalcemia (FHH) are the main differential diagnoses in a patient presenting with parathyroid hormone (PTH)-mediated hypercalcemia. PHPT is most often caused by a single-gland parathyroid adenoma and FHH is the result of an inactivating mutation of the calcium-sensing receptor (CaSR) gene. In this paper, we present a unique case of the co-existence of an inactivating CaSR gene mutation and PHPT due to a single-gland parathyroid adenoma. The patient is a 67-year-old female with a history of recurrent nephrolithiasis who presented with hypercalcemia, elevated PTH level, and hypocalciuria. As a result of the patient's hypocalciuria, familial hypocalciuric hypercalcemia was suspected, and genetic testing was pursued. CaSR gene analysis revealed a heterogeneous inactivating mutation of the CaSR gene. Additionally, nuclear imaging with technetium sestamibi revealed a large focus of activity on the right side of the neck suspicious of a parathyroid adenoma. This was resected and confirmed to be a hypercellular parathyroid adenoma. Two years after her surgery, the patient continues to have normal calcium levels with no further episodes of nephrolithiasis. She is currently undergoing treatment for osteoporosis and is being periodically monitored for recurrence of hypercalcemia due to the presence of the inactivating CaSR gene mutation. This case highlights an exceedingly rare case of a patient with both an inactivating CaSR gene mutation and PHPT due to a single parathyroid adenoma, and it underscores the importance of further research to determine any potential relationship between the two.

Case Report: Unusual Presentations of Loss-of-Function Mutations of the Calcium-Sensing Receptor

Background

In recent years, heterozygous loss-of-function mutations of the Calcium Sensing Receptor gene (CaSR) were implicated in different hypercalcemic syndromes besides familial hypocalciuric hypercalcemia (FHH), including neonatal severe primary hyperparathyroidism (NSHPT) and primary hyperparathyroidism (PHPT).

Cases presentation

Here we describe two unusual presentations of heterozygous inactivating CaSR mutations. Case 1: a case of NSHPT due to a de novo, p.(ArgR185Gln) CaSR mutation and successfully treated with cinacalcet monotherapy for 8 years until definitive surgical resolution. Case 2: a 37 years-old woman with PHPT complicated with hypercalcemia and nephrocalcinosis with a novel heterozygous p.(Pro393Arg) CaSR mutation and cured with parathyroidectomy.

Conclusions

These cases reinforce the fact that the clinical spectrum of inactivating mutations of the CaSR has widened and, although carrying a mutation suggestive of FHH, some patients may have different clinical phenotypes and complications requiring individualized therapies.

Concomitant familial hypocalciuric hypercalcemia and single parathyroid adenoma: a case report

Background

Primary hyperparathyroidism (PHPT) is a common endocrine disorder and the most frequent benign cause of hypercalcemia. PHPT is characterized by autonomous hypersecretion of parathyroid hormone (PTH), regardless of serum calcium levels. Familial hypocalciuric hypercalcemia (FHH) is a rare, benign syndrome only affecting the regulation of calcium metabolism. FHH is an autosomal-dominant genetic disease with high penetrance, caused by an inactivating variant in the CASR gene encoding the calcium-sensing receptor (CaSR). We present a unique case of concomitant PHPT and FHH without clinically actionable variants in MEN1.

Case presentation

A 47-year-old Caucasian man with severe hypercalcemia, genetic FHH, and initially normal parathyroid scintigraphy was referred for endocrine evaluation due to nonspecific symptoms. Biochemical evaluation showed elevated serum ionized calcium and PTH. The calcium–creatinine clearance ratio was low. All other biochemical measures were normal, including kidney function. Genetic evaluation was redone and confirmed FHH. A new parathyroid scintigraphy showed a significant single adenoma corresponding to the lower left gland. The patient underwent parathyroidectomy, and a parathyroid adenoma was removed. A reduced level of hypercalcemia persisted due to FHH.

Conclusions

The correct diagnosis of the underlying cause of hypercalcemia is important to ensure the right treatment. Patients with FHH should avoid operative treatment, and PHPT should be differentiated from MEN1 to determine whether surgery should include parathyroidectomy with removal of one adenoma or 3.5 hyperplastic parathyroid glands.

Clinical characteristics of familial hypocalciuric hypercalcaemia type 1: A multicentre study of 77 adult patients

OBJECTIVE

Familial hypocalciuric hypercalcaemia type 1 (FHH1), related to heterozygous loss-of-function mutations of the calcium-sensing receptor gene, is the main differential diagnosis for primary hyperparathyroidism. The aim of our study was to describe clinical characteristics of adult patients living in France with a genetically confirmed FHH1.

DESIGN AND PATIENTS

This observational, retrospective, multicentre study included 77 adults, followed up in 32 clinical departments in France, with a genetic FHH1 diagnosis between 2001 and 2012.

RESULTS

Hypercalcaemia was diagnosed at a median age of 53 years [IQR: 38-61]. The diagnosis was made after clinical manifestations, routine analysis or familial screening in 56, 34 and 10% of cases, respectively, (n = 58; data not available for 19 patients). Chondrocalcinosis was present in 11/51 patients (22%), bone fractures in 8/56 (14%) and renal colic in 6/55 (11%). The median serum calcium was 2.74 mmol/L [IQR: 2.63-2.86 mmol/L], the median plasma parathyroid hormone level was 4.9 pmol/L [3.1-7.1], and the median 24-hour urinary calcium excretion was 2.8 mmol/24 hours [IQR: 1.9-4.0]. Osteoporosis (dual X-ray absorptiometry) or kidney stones (renal ultrasonography) were found in 6/38 patients (16%) and 9/32 patients (28%), respectively. Fourteen patients (18%) underwent parathyroid surgery; parathyroid adenoma was found in three patients (21%) and parathyroid hyperplasia in nine patients (64%). No correlation between genotype and phenotype was established.

CONCLUSION

This large cohort study demonstrates that FHH1 clinical characteristics can be atypical in 33 patients (43%). Clinicians should be aware of this rare differential diagnosis in order to adopt an appropriate treatment strategy.

Case Report: Familial Hypocalciuric Hypercalcaemia and Hashimoto's Thyroiditis

Introduction: Hypercalcaemia can be caused by many disorders. Primary hyperparathyroidism is the leading cause with parathyroidectomy being the definitive management. Familial hypocalciuric hypercalcaemia is a rarer cause in which resection of the parathyroid tissue does not result in normalized serum calcium.

Case presentation: We report the unusual case of a 53-year-old lady who presented with hypercalcaemia and elevated parathyroid hormone with a presumed diagnosis of primary hyperparathyroidism. She remained hypercalcaemic after parathyroidectomy and was later diagnosed with familial hypocalciuric hypercalcaemia. During the first operation, a lymph node was also removed, and the histopathology report suggested a metastasis of follicular variant papillary thyroid carcinoma (FVPTC). After multi-disciplinary team (MDT) discussion, the patient underwent a second exploration where total thyroidectomy and removal of the other parathyroid glands were performed. Hypercalcaemia completely resolved on surgical resection of the thyroid and parathyroid tissue, however histopathology revealed normal parathyroid glands and florid Hashimoto's thyroiditis. The initial diagnosis of FVPTC in the lymph node was revisited and the final histopathology report suggested an accessory thyroid nodule with florid Hashimoto's thyroiditis mimicking a lymph node.

Conclusion: Our case demonstrates the diagnostic dilemma in hypercalcaemia that may lead a patient to undergo unnecessary invasive procedures; the misdiagnosis of FVPTC after the first operation resulted in a second more extensive procedure. Patients with no clear surgical target and urine CCCR in the gray/non-diagnostic area should be routinely offered genetic testing despite negative family history.

Diseases associated with calcium-sensing receptor

The calcium-sensing receptor (CaSR) plays a pivotal role in systemic calcium metabolism by regulating parathyroid hormone secretion and urinary calcium excretion. The diseases caused by an abnormality of the CaSR are genetically determined or are more rarely acquired. The genetic diseases consist of hyper- or hypocalcemia disorders. Hypercalcaemia disorders are related to inactivating mutations of the CASR gene either heterozygous (autosomal dominant familial benign hypercalcaemia, still named hypocalciuric hypercalcaemia syndrome type 1) or homozygous (severe neonatal hyperparathyroidism). The A986S, R990G and Q1011E variants of the CASR gene are associated with higher serum calcium levels than in the general population, hypercalciuria being also associated with the R990G variant. The differential diagnosis consists in the hypocalciuric hypercalcaemia syndrome, types 2 (involving GNA11 gene) and 3 (involving AP2S1 gene); hyperparathyroidism; abnormalities of vitamin D metabolism, involving CYP24A1 and SLC34A1 genes; and reduced GFR. Hypocalcemia disorders, which are more rare, are related to heterozygous activating mutations of the CASR gene (type 1), consisting of autosomal dominant hypocalcemia disorders, sometimes with a presentation of pseudo-Bartter’s syndrome. The differential diagnosis consists of the hypercalciuric hypocalcaemia syndrome type 2, involving GNA11 gene and other hypoparathyroidism aetiologies. The acquired diseases are related to the presence of anti-CaSR antibodies, which can cause hyper- or especially hypocalcemia disorders (for instance in APECED syndromes), determined by their functionality. Finally, the role of CaSR in digestive, respiratory, cardiovascular and neoplastic diseases is gradually coming to light, providing new therapeutic possibilities. Two types of CaSR modulators are known: CaSR agonists (or activators, still named calcimimetics) and calcilytic antagonists (or inhibitors of the CasR). CaSR agonists, such as cinacalcet, are indicated in secondary and primary hyperparathyroidism. Calcilytics have no efficacy in osteoporosis, but could be useful in the treatment of hypercalciuric hypocalcaemia syndromes.

Multiple endocrine neoplasia phenocopy revealed as a co-occurring neuroendocrine tumor and familial hypocalciuric hypercalcemia type 3

Familial hypocalciuric hypercalcemia type 3 should be considered as differential diagnosis in patients with suspected primary hyperparathyroidism and/or suspected multiple neoplasia syndrome, as correct diagnosis will spare the patients for going through multiple futile parathyroidectomies and for the worry of being diagnosed with a cancer susceptibility syndrome.

Parathyroid adenoma in a patient with familial hypocalciuric hypercalcaemia

A 57-year-old man with symptoms of fatigue, joint pains and insomnia was found to have hypercalcaemia secondary to hyperparathyroidism with a corrected calcium of 2.61 mmol/L (2.2-2.6 mmol/L) and a serum parathyroid hormone (PTH) of 86 pg/mL (10-65 pg/mL). Preoperative workup demonstrated a parathyroid adenoma in the right upper position and he proceeded to surgery. Postoperatively, however, his symptoms remained unchanged and the corrected calcium remained elevated at 2.87 mmol/L with a PTH of 59 pg/mL. He had no family history of hypercalcaemia. Further investigations revealed low 24 h urinary calcium level and a low urine calcium to creatinine ratio. Genetic testing revealed a mutation in exon 4 of the calcium sensing receptor (CaSR) confirming a diagnosis of familial hypocalciuric hyercalcaemia (FHH). The case is an example of a rare phenomenon when a parathyroid adenoma develops in patients with FHH.

Novel inactivating mutation of the calcium-sensing receptor in a young woman with mild hypercalcaemia

A young woman with mild hypercalcaemia and an inappropriately normal serum parathyroid hormone had parathyroid scintigraphy suggestive of an active ectopic parathyroid tissue in the superior mediastinum. Urinary calcium to creatinine clearance ratio was low, and a subsequent genetic analysis confirmed a novel mutation (Q164K) in the calcium sensing receptor gene, consistent with familial hypocalciuric hypercalcaemia. We propose that this mutation accounts for her clinical and investigational findings, although a double pathology of Q164K and an ectopic parathyroid adenoma is also conceivable.