Browsing by Author "Thakker, Rajesh V."

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    Mutations affecting G-protein subunit α11 in hypercalcemia and hypocalcemia
    (Massachusetts Medical Society, 2013) Nesbit, M. Andrew; Hannan, Fadil M.; Howles, Sarah A.; Babinsky, Valerie N.; Head, Rosie A.; Cranston, Treena; Rust, Nigel; Hobbs, Maurine R.; Heath, Hunter, III; Thakker, Rajesh V.; Medicine, School of Medicine
    Background: Familial hypocalciuric hypercalcemia is a genetically heterogeneous disorder with three variants: types 1, 2, and 3. Type 1 is due to loss-of-function mutations of the calcium-sensing receptor, a guanine nucleotide-binding protein (G-protein)-coupled receptor that signals through the G-protein subunit α11 (Gα11). Type 3 is associated with adaptor-related protein complex 2, sigma 1 subunit (AP2S1) mutations, which result in altered calcium-sensing receptor endocytosis. We hypothesized that type 2 is due to mutations effecting Gα11 loss of function, since Gα11 is involved in calcium-sensing receptor signaling, and its gene (GNA11) and the type 2 locus are colocalized on chromosome 19p13.3. We also postulated that mutations effecting Gα11 gain of function, like the mutations effecting calcium-sensing receptor gain of function that cause autosomal dominant hypocalcemia type 1, may lead to hypocalcemia. Methods: We performed GNA11 mutational analysis in a kindred with familial hypocalciuric hypercalcemia type 2 and in nine unrelated patients with familial hypocalciuric hypercalcemia who did not have mutations in the gene encoding the calcium-sensing receptor (CASR) or AP2S1. We also performed this analysis in eight unrelated patients with hypocalcemia who did not have CASR mutations. In addition, we studied the effects of GNA11 mutations on Gα11 protein structure and calcium-sensing receptor signaling in human embryonic kidney 293 (HEK293) cells. Results: The kindred with familial hypocalciuric hypercalcemia type 2 had an in-frame deletion of a conserved Gα11 isoleucine (Ile200del), and one of the nine unrelated patients with familial hypocalciuric hypercalcemia had a missense GNA11 mutation (Leu135Gln). Missense GNA11 mutations (Arg181Gln and Phe341Leu) were detected in two unrelated patients with hypocalcemia; they were therefore identified as having autosomal dominant hypocalcemia type 2. All four GNA11 mutations predicted disrupted protein structures, and assessment on the basis of in vitro expression showed that familial hypocalciuric hypercalcemia type 2-associated mutations decreased the sensitivity of cells expressing calcium-sensing receptors to changes in extracellular calcium concentrations, whereas autosomal dominant hypocalcemia type 2-associated mutations increased cell sensitivity. Conclusions: Gα11 mutants with loss of function cause familial hypocalciuric hypercalcemia type 2, and Gα11 mutants with gain of function cause a clinical disorder designated as autosomal dominant hypocalcemia type 2.
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    Presentation of Hypoparathyroidism: Etiologies and Clinical Features
    (Endocrine Society, 2016-06) Shoback, Dolores M.; Bilezikian, John P.; Costa, Aline G.; Dempster, David; Dralle, Henning; Khan, Aliya A.; Peacock, Munro; Raffaelli, Marco; Silva, Barbara C.; Thakker, Rajesh V.; Vokes, Tamara; Bouillon, Roger; Department of Medicine, IU School of Medicine
    tanding the etiology, diagnosis, and symptoms of hypoparathyroidism may help to improve quality of life and long-term disease outcomes. This paper summarizes the results of the findings and recommendations of the Working Group on Presentation of Hypoparathyroidism. Evidence Acquisition: Experts convened in Florence, Italy, in May 2015 and evaluated the literature and recent data on the presentation and long-term outcomes of patients with hypoparathyroidism. Evidence Synthesis: The most frequent etiology is surgical removal or loss of viability of parathyroid glands. Despite precautions and expertise, about 20–30% of patients develop transient and 1–7% develop permanent postsurgical hypoparathyroidism after total thyroidectomy. Autoimmune destruction is the main reason for nonsurgical hypoparathyroidism. Severe magnesium deficiency is an uncommon but correctable cause of hypoparathyroidism. Several genetic etiologies can result in the loss of parathyroid function or action causing isolated hypoparathyroidism or a complex syndrome with other symptoms apart from those of hypoparathyroidism or pseudohypoparathyroidism. Neuromuscular signs or symptoms due to hypocalcemia are the main characteristics of the disease. Hyperphosphatemia can contribute to major long-term complications such as ectopic calcifications in the kidney, brain, eye, or vasculature. Bone turnover is decreased, and bone mass is increased. Reduced quality of life and higher risk of renal stones, renal calcifications, and renal failure are seen. The risk of seizures and silent or symptomatic calcifications of basal ganglia is also increased. Conclusions: Increased awareness of the etiology and presentation of the disease and new research efforts addressing specific questions formulated during the meeting should improve the diagnosis, care, and long-term outcome for patients.