Dysregulation of calcium metabolism in type 1 myotonic dystrophy.

BACKGROUND: Patients with type 1 myotonic dystrophy (DM1) have a higher incidence of hypercalcaemia compared with the general population. The nature and effects of dysregulated calcium metabolism underpinning this phenomenon have not been fully characterised. AIMS: To determine the characteristics of dysregulated calcium metabolism in patients with DM1 and its association with bone mineral density. METHODS: A retrospective review of medical records of patients with DM1 attending a DM clinic at Logan Hospital, Brisbane, Queensland, between 2005 and 2018 and who had concurrent serum assays performed of corrected serum calcium, 25 hydroxyvitamin D, parathyroid hormone (PTH) and phosphate and for whom results were available for estimated glomerular filtration rate, bone mineral densitometry tests and urinary calcium clearance to creatinine clearance ratio (UCCR). RESULTS: Forty-four patients with DM1 (22 females, 22 males) were reviewed of whom 14 (32%) had elevated corrected serum calcium and inappropriate PTH. Another 10 patients (23%) had raised PTH with normocalcaemia. Eighteen of 19 (94.7%) patients with hypercalcaemia or high PTH level completed 24-h urinary calcium. All had UCCR ≤0.02. Twelve patients had UCCR <0.01. Seven of 44 (16%) had low 25 hydroxy vitamin D. All patients had normal estimated glomerular filtration rate. None was osteoporotic. CONCLUSIONS: One in three patients with DM1 was hypercalcaemic with unsuppressed PTH. Their clinical features and biochemical pictures resemble those of familial hypocalciuric hypercalcaemia (FHH) and raises the possibility that impaired activity of calcium-sensing receptors, due to abnormal splicing of the calcium-sensing receptor messenger RNA in DM1, causes a FHH-like syndrome ('pseudo-FHH of DM1').

Glucocorticoid receptor polymorphisms and post-traumatic stress disorder.

Post-traumatic stress disorder (PTSD) is reported in some studies to be associated with increased glucocorticoid (GC) sensitivity. Two common glucocorticoid receptor (GR) polymorphisms (N363S and BclI) appear to contribute to the population variance in GC sensitivity. There is some evidence that there may be a genetic predisposition to PTSD. Hence we studied 118 Vietnam war veterans with PTSD for (i) GR polymorphisms, particularly the N363S and the BclI polymorphisms which are thought to be GC sensitising, and (ii) two measures of GC sensitivity, the low-dose 0.25 mg dexamethasone suppression test (LD-DST) and the dermal vasoconstrictor assay (DVVA). The DST and GR polymorphisms were also performed in 42 combat exposed Vietnam war veterans without PTSD. Basal plasma cortisol levels were not significantly different in PTSD (399.5+/-19.2 nmol/L, N=75) and controls (348.6+/-23.0 nmol/L, N=33) and the LD-DST resulted in similar cortisol suppression in both groups (45.6+/-3.2 vs. 40.8+/-4.1%). The cortisol suppression in PTSD patients does not correlate with Clinician Administered PTSD Scores (CAPS), however there was a significant association between the BclI GG genotype and low basal cortisol levels in PTSD (P=0.048). The response to the DVVA was similar to controls (945+/-122, N=106 vs. 730+/-236, N=28, P=0.42). PTSD patients with the GG genotype, however, tended to be more responsive to DVVA and in this group the DVVA correlated with higher CAPS scores. The only exon 2 GR polymorphisms detected were the R23K and N363S. Heterozygosity for the N363S variant in PTSD, at 5.1% was not more prevalent than in other population studies of the N363S polymorphism in Caucasians (6.0-14.8%). The GG genotype of the BclI polymorphism found to be associated with increased GC sensitivity in many studies showed a tendency towards increased response with DVVA and correlated with higher CAPS scores. In conclusion, the N363S and BclI GR polymorphisms were not more frequent in PTSD patients than controls and reported population frequencies. Our PTSD group did not display GC hypersensitivity, as measured by the LD-DST and DVVA. In a subset of PTSD patients with the BclI GG genotype, CAPS scores and basal cortisol levels were negatively correlated.

New genetic insights in familial hyperaldosteronism.

Aldosterone, the major circulating mineralocorticoid, particiates in blood volume and serum potassium homeostasis. Primary aldosteronism is a disorder characterized by hypertension and, in more severe form, hypokalemia, due to autonomous aldosterone secretion from the adrenocortical zona glomerulosa. Improved screening techniques, particularly application of the plasma aldosterone: plasma renin activity ratio, has led to renewed interest in Conn's original proposal that primary aldosteronism may be the cause of increased blood pressure in about 10% of adults with hypertension. Glucocorticoid-remediable aldosteronism (GRA) was the first described familial form of hyperaldosteronism. The disorder is characterized by aldosterone secretory function regulated chronically by ACTH. Hence, aldosterone hypersecretion can be chronically suppressed by exogenous glucocorticoids such as dexamethasone in physiologic-range doses. This autosomal dominant disorder has been shown to be caused by a hybrid gene mutation formed by a cross-over of genetic material between the ACTH-responsive regulatory portion of the 11b-hydroxylase (CYP11B1) gene and the coding region of the aldosterone synthase (CYP11B2) gene. Familial hyperaldosteronism type II (FH-II), so named to distinguish the disorder from GRA or familial hyperaldosteronism type I (FH-I), is characterized by inheritance consistent with an autosomal dominant pattern of autonomous aldosterone hypersecretion which is not suppressible by dexamethasone. Linkage analysis in a single large kindred, and direct mutation screening, has shown that this disorder is unrelated to mutations in the genes for aldosterone synthase or the angiotensin II receptor. A recent genome-wide search has identified a genetic linkage between FH-II in this single large kindred and polymorphic gene markers on chromosome 7 in a region that corresponds to cytogenetic band 7p22. This is the first identified locus for FH-II. Several possible candidate genes have been localized to the 7p22 region. The precise genetic cause of FH-II remains to be elucidated.