T h e new england journal o f medicine of a meta-analysis of studies of the effect of re- terone levels were increased. Although long- duced dietary salt on the incidence of cardiovas- term, modest reductions in salt intake result in cular events and death.1 The authors of the Co- small, physiologic increases in plasma renin ac- chrane report wrote that there was “no strong tivity,3 the preponderance of evidence suggests evidence of benefit.” In a summary statement, we that a reduced salt intake is associated with a wrote that this particular Cochrane analysis con- decreased risk of cardiovascular events and cluded that reducing dietary salt intake did not death. Furthermore, it is worth remembering decrease the risk of death or cardiovascular dis- that diuretics remain one of the most effective ease. Stigler et al. suggest that “indeterminate antihypertensive therapies, and their beneficial results,” rather than no significant effect, would effect on cardiovascular disease is well docu- be a more appropriate interpretation of the analy- mented.4 Nevertheless, as we suggested, in sis. Both interpretations may be correct. Although terms of safety, the lower limit of salt consump- it may not be possible to reject the null hypothe- tion has not been clearly defined. sis with certainty (i.e., no effect of reduced salt), Theodore A. Kotchen, M.D. the analysis should have been powered to detect Allen W. Cowley, Jr., Ph.D. a clinically meaningful difference, and the con- Medical College of Wisconsin clusion of no effect provides more guidance than Milwaukee, WI “indeterminate results” to clinical decision mak- [email protected] ers. Focusing on these subtleties, however, miss- Edward D. Frohlich, M.D. es the point we made regarding the Cochrane re- Ochsner Medical Center port. As analyzed by others2 and as cited in our New Orleans, LA review, after the exclusion of a trial involving pa- Since publication of their article, the authors report no fur- ther potential conflict of interest. tients with heart failure who received aggressive diuretic therapy and combining data for patients 1. Taylor RS, Ashton KE, Moxham T, Hooper L, Ebrahim S. Reduced dietary salt for the prevention of cardiovascular dis- with and without hypertension, reduced salt in- ease: a meta-analysis of randomized controlled trials (Cochrane take was shown to be associated with a signifi- review). Am J Hypertens 2011;24:843-53. cant reduction in the rate of cardiovascular 2. He FJ, MacGregor GA. Salt reduction lowers cardiovascular risk: meta-analysis of outcome trials. Lancet 2011;378:380-2. events. 3. He FJ, Li J, Macgregor GA. Effect of longer term modest salt Thornton raises important questions: do rec- reduction on blood pressure: Cochrane systematic review and ommended reductions of dietary sodium stimu- meta-analysis of randomised trials. BMJ 2013;346:f1325. 4. Chobanian AV, Bakris GL, Black HR, et al. The Seventh Re- late the renin–angiotensin–aldosterone axis, and port of the Joint National Committee on Prevention, Detection, does this in turn contribute to cardiovascular Evaluation, and Treatment of High Blood Pressure: the JNC 7 disease? In trials of abrupt and severe salt re- report. JAMA 2003;289:2560-72. [Erratum, JAMA 2003;290:197.] striction, plasma renin activity and serum aldos- DOI: 10.1056/NEJMc1305326 Germline Mutations Affecting Gα11 in Hypoparathyroidism To the Editor: Extracellular calcium levels are laboratory findings consistent with autosomal tightly regulated by parathyroid hormone (PTH). dominant isolated hypoparathyroidism (Fig. 1). Insufficient production of this hormone, as ob- After ruling out the presence of mutations in served in nonsyndromic isolated hypoparathy- CaSR, PTH, and GCM2 in the index cases (not roidism, can be caused by mutations in PTH or shown), a genomewide scan revealed linkage the genes encoding the parathyroid-specific to a single chromosomal region for Family A transcription factor glial cells missing 2 (GCM2) (19p13.3; LOD score, 3.0). Candidate gene se- or the calcium-sensing receptor (CaSR). However, quencing resulted in the identification of a hetero- most cases of isolated hypoparathyroidism re- zygous nucleotide change in exon 2 of GNA11 main genetically undefined.1 (c.178C→T; p.Arg60Cys), the gene encoding the We investigated two unrelated white families α subunit of the guanine nucleotide-binding in which 15 living members had clinical and protein G11 (Gα11) (Fig. S1 in the Supplementary 2532 n engl j med 368;26 nejm.org june 27, 2013 correspondence Family A Family B 21 11 12 13 2 5 5 31 37 38 32 21 23 24 27 26 25 41 42 43 44 32 31 Patient No. Patient No. Variable 31 42 21 41 32 43 44 37 38 Variable 32 21 31 23 11 24 27 26 25 12 13 Calcium 2.25 2.10 2.19 2.27 2.08 2.25 2.16 2.06 1.98 Calcium 1.92 1.88 1.84 1.90 1.81 1.80 2.12 2.00 2.40 low nl. (2.15–2.70 mM) (2.10–2.55 mM) Phosphorus 1.25 2.30 n.d. 1.16 1.39 1.75 3.06 1.63 1.23 Phosphorus 2.37 1.48 2.35 1.48 1.72 1.58 1.79 1.58 0.99 elev. nl. (0.70–1.40 mM) (0.80–1.50 mM) PTH 5.90 1.20 3.00 8.20 0.90 4.10 1.70 n.d. n.d. PTH 3.00 0.90 1.50 0.90 1.60 0.90 0.64 1.16 0.90 nl. nl. (1.0–7.0 pmol/liter) (1.6–6.9 pmol/liter) bp bp 646 — 360 — 509 202 — 158 — 137 — 360 bp 646 bp Mutated Mutated 158 bp 202 bp 509 bp 137 bp Nonmutated Nonmutated FspI BsiEI Figure 1. Pedigrees and Laboratory and Genetic Findings for Two Families with Autosomal Dominant Isolated Hypoparathyroidism. Squares indicate male family members, circles female family members, black symbols affected family members, and white symbols un- affected family members; slashes indicate deceased family members; numbers outside squares and circles indicate family members for whom DNA was available for testing; numbers within white rhombi indicate the number of unaffected siblings. Arrows point to the index cases. Measurements for calcium, phosphorus, and parathyroid hormone (PTH) are shown (with adult normal ranges in parentheses) and reflect values at presentation except in the case of Patients 21 and 32, from whom samples were drawn after treatment was initiated. For affected members, mean (±SE) pretreatment serum levels of calcium were 2.15±0.02 mmol per liter in Family A and 1.91±0.04 mmol per liter in Family B, mean levels of phosphorus were 2.06±0.40 and 1.79±0.13 mmol per liter, respectively, and mean levels of PTH were 1.97±0.42 and 1.33±0.27 pmol per liter, respectively. Values for other variables among patients with autosomal dominant isolated hypo- parathyroidism for whom mean pretreatment levels were available were as follows: magnesium, 0.77±0.02 mmol per liter (10 patients; normal range, 0.7 to 1.0); 1,25-dihydroxyvitamin D, 81.8±10.0 pmol per liter (8 patients; normal range, 40 to 150); and urinary calcium:creatinine ratio, normal when measured (8 patients; normal range, <0.6 mmol:mmol). Two novel mutations affecting Gα11 (R60C and S211W) were identified by means of genetic linkage analysis for Family A and exome sequencing of a DNA sample from two affected members of Families A and B (see Fig. 1 in the Supplementary Appendix). Digestion of DNA (amplified by means of polymerase chain reaction) with the endonucleases FspI and BsiEI, respectively, confirmed the two mutations and revealed their segregation with the disease. Appendix, available with the full text of this let- identified. The nucleotide changes were present ter at NEJM.org). Whole-exome sequencing of only in affected family members, and both two affected members of Family A (Patients 37 changes affect amino acid residues that are and 44) confirmed this nucleotide transition. highly conserved in Gα11 and the closely relat- Exome sequencing of two members of Family B ed Gαq. (Patients 26 and 31) revealed a heterozygous Gα11 and Gαq mediate the intracellular sig- nucleotide transversion in exon 5 of GNA11 naling that depends on the generation of inositol (c.632C→G; p.Ser211Trp); no additional variant 1,4,5-trisphosphate and the activation of protein that affects the same gene in both families was kinase C and occurs downstream of CaSR,2 the n engl j med 368;26 nejm.org june 27, 2013 2533 T h e new england journal o f medicine main regulator of PTH synthesis and secretion. bined with whole-exome sequencing, revealed Homozygous inactivating CaSR mutations cause two different heterozygous mutations affecting severe neonatal hyperparathyroidism, as does the Gα11 as novel causes of autosomal dominant combined parathyroid-specific ablation of Gα11 isolated hypoparathyroidism. 3,4 and Gαq in mice. Conversely, activating CaSR Michael Mannstadt, M.D. mutations lead to hypocalcemia because of inap- Massachusetts General Hospital propriate PTH secretion.1 The latter findings Boston, MA are similar to those reported for our families Mark Harris, M.D. with autosomal dominant isolated hypoparathy- Mater Children’s Hospital roidism, thus making it plausible to suggest that Brisbane, QLD, Australia the identified Gα11 mutants increase signaling Bert Bravenboer, M.D., Ph.D. at this receptor. Catharina Ziekenhuis To evaluate this hypothesis, we analyzed both Eindhoven, the Netherlands mutants with the use of molecular modeling Sridhar Chitturi, M.B., B.S., M.D. (Fig. S2 in the Supplementary Appendix). On the Royal Darwin Hospital Tiwi, NT, Australia basis of the proposed crystal structure of Gα11, it is probable that the replacement of arginine 60 Koen M.A.