Abnormal calcium metabolism in myotonic dystrophy (II): Increased level of nephrogenous cyclic AMP and serum immunoreactive parathyroid hormone

Abstract

Myotonic dystrophy (MyD) is a multisystemic disorder characterized by muscle atrophy, myotonia and cataract. Although a number of reports have been accumulated showing the presence of bone changes in MyD patients, there are few published papers in which calcium metabolism was precisely examined. In the previous paper, we reported that intestinal calcium absorption was increased in MyD patients due to the elevation of plasma 1,25(OH)2D level. The present study was designed to elucidate the mechanism of increased level of serum 1,25(OH)2D concentration in MyD patients. Calcium tolerance tests were performed in 13 patients with MyD, 13 patients with other neuromuscular disorders (non-MyD) and 12 healthy control subjects according to the method of Broadus et al. Immunoreactive PTH (iPTH) levels and cyclic AMP (cAMP) levels were measured using commercially available RIA kits. The basal plasma calcium levels in MyD were slightly higher than those in the other two groups, but the difference was not statistically significant. The plasma 1,25(OH)2D levels, calcemic responses and calciuric responses in MyD were significantly higher than those in the other two groups. Serum iPTH levels in MyD (0.462 +/- 0.320 ng/ml, Mean +/- SD) were significantly higher than those in the other two groups (normal subjects 0.175 +/- 0.092, non-MyD 0.200 +/- 0.111; p less than 0.02). Nephrogenous cyclic AMP (NcAMP) levels in MyD (2.094 +/- 3.244 nmol/100 ml GF) were also higher than those in normal subjects (0.907 +/- 0.212, p less than 0.05) and in non-MyD (0.929 +/- 0.335, p less than 0.05). There was a significant correlation between serum iPTH levels and NcAMP levels, and therefore it might be possible to accept that these two measurements reflect the level of parathyroid function.(ABSTRACT TRUNCATED AT 250 WORDS)