Hyperparathyroid and hypoparathyroid disorders

Hyperparathyroidism in elderly osteopenic women

Raised levels of parathyroid hormones (PTH) predispose to osteoporotic fracture particularly in the elderly. The true prevalence of primary or secondary hyperparathyroidism is unknown, as PTH evaluation is not performed as a screening test in the elderly. We report raised PTH levels in 27 of 190 (14.2%) community living fully mobile postmenopausal women with densitometrically established osteopenia, consuming an average of 645 (+/-191) mg of calcium per day. Twenty-five of the 27 women with raised PTH were normocalcaemic, hypercalcaemia been found only in two. Serum 25 hydroxy vitamin D levels were all within the normal range (above 22 nmol/l). Women with a raised PTH were significantly older and their serum 25 hydroxy vitamin D levels were significantly lower than those women with normal PTH values. These data suggest that in community leaving healthy postmenopausal women, normocalcaemic hyperparathyroidism, in the presence of what are still considered normal vitamin D levels, may be common. This may suggests that widespread supplementation with calcium and vitamin D may be required in postmenopausal women for PTH suppression and preservation of bone mass.

HRPT2, encoding parafibromin, is mutated in hyperparathyroidism-jaw tumor syndrome

We report here the identification of a gene associated with the hyperparathyroidism-jaw tumor (HPT-JT) syndrome. A single locus associated with HPT-JT (HRPT2) was previously mapped to chromosomal region 1q25-q32. We refined this region to a critical interval of 12 cM by genotyping in 26 affected kindreds. Using a positional candidate approach, we identified thirteen different heterozygous, germline, inactivating mutations in a single gene in fourteen families with HPT-JT. The proposed role of HRPT2 as a tumor suppressor was supported by mutation screening in 48 parathyroid adenomas with cystic features, which identified three somatic inactivating mutations, all located in exon 1. None of these mutations were detected in normal controls, and all were predicted to cause deficient or impaired protein function. HRPT2 is a ubiquitously expressed, evolutionarily conserved gene encoding a predicted protein of 531 amino acids, for which we propose the name parafibromin. Our findings suggest that HRPT2 is a tumor-suppressor gene, the inactivation of which is directly involved in predisposition to HPT-JT and in development of some sporadic parathyroid tumors.

Independent genetic events associated with the development of multiple parathyroid tumors in patients with primary hyperparathyroidism

Multiple parathyroid tumors, as opposed to hyperplasia, have been reported in a subset of patients with sporadic primary hyperparathyroidism (PHPT). It is not clear whether these multiple tumors are representative of a neoplastic process or whether they merely represent hyperplasia that has affected the parathyroid glands differentially and resulted in asynchronous growth. The molecular genetic techniques of comparative genomic hybridization (CGH), loss of heterozygosity (LOH), and MEN1 mutation analysis were performed on a series of five patients with multiglandular PHPT, each of which had two parathyroid tumors removed. Analysis of these multiple parathyroid tumors from patients with PHPT revealed that independent genetic events were associated with the development of a subset of these tumors. The DNA sequence copy number changes, identified by CGH analyses, either involved different chromosomal regions in the paired glands of a patient (two patients), or those regions implicated in one gland were not changed in a second gland from the same patient (two patients). Each of the three patients exhibiting LOH demonstrated different changes between the paired glands. Where LOH was detected in one gland from a patient, the other gland from the same patient either exhibited no allelic loss or the loss detected was in another region. Each of the three tumors exhibiting LOH at 11q13 was found to contain a somatic MEN1 mutation in the remaining allele, however these mutations were not present in the germline or in the paired gland from the same patient. Although it is possible that a separate series of genetic changes has arisen randomly in two separate glands within the same individual, it seems more likely that the development of these multiple tumors has arisen because of the involvement of other unknown factors. These factors may be genetic [such as the involvement of one or more germline mutations in an unknown low-penetrance gene(s), germline mosaicism or alterations in calcium-sensing receptor gene(s)], epigenetic, physiological, or environmental.

Hypercalcemia in malignant and inflammatory diseases

Hypercalcemia is one of the most common metabolic abnormalities in human disease. Although there are many causes, most cases are due to neoplasia. Understanding the pathophysiology can lead to correct diagnosis and effective therapy for most patients.

Chronic hypocalcaemia due to selective skeletal resistance to parathyroid hormone

A 71-year-old man was referred for evaluation of asymptomatic hypocalcaemia dating back at least 20 years. There were no somatic abnormalities and Chvostek and Trousseau signs were negative. Serum total calcium varied from 1.88 to 2.03 mmol/l, albumin 37-44 g/l, phosphate 0.54-1.12 mmol/l and ionized calcium 1-1.13 mmol/l. Serum intact PTH levels were 69 and 55 ng/l (10-65), 25-OHD was 40 nmol/l (2.25-107.5) and 1,25-(OH)2D was 54.6 nmol/l (39-156). Serum and urine magnesium and creatinine clearance were normal. Twenty-four-hour urine calcium was 2.15 mmol and calcium/creatinine ratio 0.07. TM phosphate (maximal rate of tubular reabsorption of phosphate in mmol/l glomerular filtrate (GF)) was 0.84 mmol/l GF (0.80-1.34). Bone formation and resorption markers were normal. Bone mineral densities measured by dual-energy X-ray absorptiometry (DEXA) were within normal limits at the hip, forearm and lumbar spine. Infusion of 200 units of synthetic 1-34 PTH was associated with a rise in urinary cyclic AMP from 43 mmol/l GF to 344 mmol/l GF and TM phosphate fell from 0.93 to 0.76 mmol/l GF; 1-34 PTH infusions of 300 units twice daily for 5 days were associated with an increase in serum 1,25-(OH)2D from 80.6 to 114.4 pmol/l but no increase in serum calcium. This is a most unusual case of chronic hypocalcaemia similar to that reported by Frame et al. resulting from isolated skeletal resistance to PTH that is not related to renal insufficiency, osteomalacia or a magnesium-deficient state. These two cases appear to represent a new variant of pseudohypoparathyroidism ?type III.

Hypocalcemia in the newborn

Healthy term babies undergo a physiological nadir in serum calcium levels by 24-48 hours of age. This nadir may be related to the delayed response of parathyroid and calcitonin hormones in a newborn. This nadir may drop to hypocalcemic levels in high-risk neonates including infants of diabetic mothers, preterm infants and infants with perinatal asphyxia. This early onset hypocalcemia which presents within 72 hours, requires treatment with calcium supplementation for at least 72 hours. In contrast late onset hypocalcemia usually presents after 7 days and requires long term therapy. Ionized calcium is crucial for many biochemical processes and total serum calcium is a poor substitute for the diagnosis of hypocalcemia.