Hypercalcitoninaemia in pseudohypo-parathyroidism type 1A and type 1B

STX16 exon 5-7 deletion in a patient with pseudohypoparathyroidism type 1B

OBJECTIVES

Pseudohypoparathyroidism (PHP) comprises a cluster of heterogeneous diseases characterized by hypocalcemia and hyperphosphatemia due to parathyroid hormone (PTH) resistance. PHP type 1B (PHP1B) is caused by heterozygous maternal deletions within GNAS or STX16. STX16 exon 2-6 deletion is commonly observed in autosomal dominant (AD)-PHP1B, while sporadic PHP1B commonly results from methylation abnormalities of maternal differentially methylated regions and remains unclear at the molecular level.

CASE PRESENTATION

A 39-year-old male patient with PHP1B, who had his first seizure at 15 years of age, presented to our hospital. The methylation-specific multiplex ligation-dependent probe amplification results showed a half-reduced copy number of STX16 exon 5-7 and loss of methylation at GNAS exon A/B. His mother also had a half-reduced copy number of STX16 exon 5-7 but with normal methylation of GNAS. His father has a normal copy number of STX16 and normal methylation of GNAS.

CONCLUSIONS

For the recognition and early diagnosis of this kind of disease, here we report the clinical symptoms, auxiliary examinations, genetic testing characteristics, and treatment of the patient.

Autosomal dominant pseudohypoparathyroidism type 1b due to STX16 deletion: a case presentation and literature review

INTRODUCTION

Pseudohypoparathyroidism (PHP) is a heterogeneous group of rare, genetically related, endocrine disorders, characterized by end-organ resistance to parathyroid hormone (PTH) action and other G protein-coupled receptors (GPCRs) related hormones. The clinical variants of PHP are classified according to the presence of features of Albright's hereditary osteodystrophy (AHO) and in vivo response to exogenous PTH. Autosomal dominant PHP1b is often caused by a deletion in the syntaxin-16 (STX16) gene, leading to a loss of methylation in the A/B exon of the guanine nucleotide-binding protein a-stimulating polypeptide (GNAS) complex. Herein, we present a case of a 41-year-old man with familiar PHP1b due to a maternal inherited 3-kb STX16 deletion, who was referred to us for consultation by artificial reproductive technology specialists.

EVIDENCE ACQUISITION

A bibliographic search was performed in electronic databases (PubMed and Cochrane Library) to identify similar cases.

EVIDENCE SYNTHESIS

Twenty studies (case-series or reports) were eligible. These studies included collectively 120 patients; 46 patients (38.3%) presented with symptoms of hypocalcemia; 38 were asymptomatic (31.7%); data for 36 patients (30%) were unavailable. Thyroid-stimulating hormone (TSH) resistance was documented in 25 occasions (21%); growth hormone deficiency in 2 (1.7%); 3 patients shared features of the AHO (2.5%); 6 had abnormal bone mineral density test (5%). Notable is the development of tertiary hyperparathyroidism in 3 individuals (2.5%).

CONCLUSIONS

The present review confirms the heterogeneity in the clinical spectrum of familiar PHP1b. Future research should focus on the molecular characterization of the GNAS disorders, leading to a facile diagnosis and appropriate genetic counseling.

C-Cell Hyperplasia and Cystic Papillary Thyroid Carcinoma in a Patient with Type 1B Pseudohypoparathyroidism and Hypercalcitoninaemia: Case Report and Review of the Literature

Hypercalcitoninaemia has been described in patients with pseudohypoparathyroidism (PHP) type 1A and 1B. Elevated calcitonin levels are thought to result from impaired Gsα receptor signaling, leading to multiple hormone resistance. Evidence on the risk of medullary thyroid carcinoma (MTC) or C-cell hyperplasia in PHP patients with hypercalcitoninaemia is lacking. A 43-year-old Caucasian man was referred to our endocrinology clinic for chronic hypocalcemia associated with elevated serum parathormone levels and a single cystic thyroid nodule. The patient did not show skeletal deformities, and screening for concomitant hormone resistances was negative, except for the presence of elevated serum calcitonin levels. The workup led to a molecular diagnosis of sporadic PHP1B. Fine needle aspiration of the thyroid nodule was not diagnostic. The calcium stimulation test yielded an abnormal calcitonin response. Given the scarcity of data on the risk of thyroid malignancy in PHP and calcium stimulation test results, total thyroidectomy was performed. Histological examination revealed cystic papillary thyroid cancer in a background of diffuse C-cell hyperplasia. To our knowledge, we are the first to describe a rare form of thyroid cancer combined with C-cell hyperplasia in a patient with PHP and hypercalcitoninaemia. In the present case, a mere receptor resistance might not fully explain the elevated calcitonin levels, suggesting that hypercalcitoninaemia should be carefully evaluated in PHP patients, especially in the case of concomitant thyroid nodules. Further studies on larger cohorts are needed to elucidate this topic.