The effects of inheritance on constituents of plasma: a twin study on some biochemical variables

Genetic and Environmental Correlation Analysis of Serum Creatinine Levels in Chinese Twins

Almost all creatinine is excreted by the kidney in individuals. Serum creatinine concentration, a widely used renal function index in clinical practice, can be affected by both genetic and environmental factors, as evidenced by current research exploring the relationship between these factors and kidney function. However, few studies have explored the heritability of serum creatinine in Asian populations. Therefore, we explored the genetic and environmental factors that affect the serum creatinine level in Asian populations. Participants in this study came from the Qingdao Twin Registry in China, and 374 pairs of twins were included, of which 139 pairs were dizygotic twins, whose ages ranged from 40 to 80 years old, and the serum creatinine level ranged from 10 to 126 μmol/L. Structural equation models were constructed using Mx software to calculate heritability, with adjusted covariates being age, sex, and body mass index. The results of heritability analysis showed that ACE was the best fit model. Serum creatinine level is influenced by genetic and environmental factors. The result of heritability was 35.44%, and the influence of shared environmental factors accounted for 52.13%. This study provided the relevant basis for future research on genetic and environmental factors affecting serum creatinine levels in Asian populations.

The Heritability of Kidney Function Using an Older Australian Twin Population

Introduction

Twin studies are unique population models which estimate observed rather than inferred genetic components of complex traits. Nonmonogenic chronic kidney disease (CKD) is a complex disease process with strong genetic and environmental influences, amenable to twin studies. We aimed to assess the heritability of CKD using twin analysis and modeling within Older Australian Twin Study (OATS) data.

Methods

OATS had 109 dizygotic (DZ) and 126 monozygotic (MZ) twin pairs with paired serum creatinine levels. Heritability of kidney function as estimated glomerular filtration rate (eGFR CKD Epidemiology Collaboration [CKD-EPI]) was modeled using the ACE model to estimate additive heritability (A), common (C), and unique (E) environmental factors. Intratwin pair analysis using mixed effects logistic regression allowed analysis of variation in eGFR from established CKD risk factors.

Results

The median age was 69.71 (interquartile range 78.4-83.0) years, with 65% female, and a mean CKD-EPI of 82.8 ml/min (SD 6.7). The unadjusted ACE model determined kidney function to be 33% genetically determined (A), 18% shared genetic-environmental (C), and 49% because of unique environment (E). This remained unchanged when adjusted for age, hypertension, and sex. Hypertension was associated with eGFR; however, intertwin variance in hypertension did not explain variance in eGFR. Two or more hypertension medications were associated with decreased eGFR (P = 0.009).

Conclusion

This study estimates observed heritability at 33%, notably higher than inferred heritability in genome-wide association study (GWAS) (7.1%-18%). Epigenetics and other genomic phenomena may explain this heritability gap. Difference in antihypertension medications explains part of unique environmental exposures, though discordance in hypertension and diabetes does not.

The genetics of kidney stone disease and nephrocalcinosis

Kidney stones (also known as urinary stones or nephrolithiasis) are highly prevalent, affecting approximately 10% of adults worldwide, and the incidence of stone disease is increasing. Kidney stone formation results from an imbalance of inhibitors and promoters of crystallization, and calcium-containing calculi account for over 80% of stones. In most patients, the underlying aetiology is thought to be multifactorial, with environmental, dietary, hormonal and genetic components. The advent of high-throughput sequencing techniques has enabled a monogenic cause of kidney stones to be identified in up to 30% of children and 10% of adults who form stones, with ~35 different genes implicated. In addition, genome-wide association studies have implicated a series of genes involved in renal tubular handling of lithogenic substrates and of inhibitors of crystallization in stone disease in the general population. Such findings will likely lead to the identification of additional treatment targets involving underlying enzymatic or protein defects, including but not limited to those that alter urinary biochemistry.

Health Effects of Calcium: Evidence From Mendelian Randomization Studies

Calcium is widely used in conjunction with vitamin D to prevent osteoporosis. The use of calcium supplementation is also promoted for its potential benefits in lowering the risk for metabolic syndromes and cancers. However, the causal link between calcium and various health outcomes remains unclear. This review focuses on the evidence from 24 Mendelian randomization (MR) studies that were designed to minimize bias from confounding and reverse causation. These MR studies evaluated the effect of lifelong genetically higher serum calcium levels on various health outcomes. Overall, available MR studies found no conclusive effects of serum calcium levels on bone mineral density and fracture, ischemic stroke and heart failure, cancers, type 2 diabetes, Parkinson disease, or offspring birth weight. However, a higher serum calcium concentration was reported to have estimated causal effects on increased risks for coronary artery disease (especially myocardial infarction), migraine, renal colic, allergy/adverse effect of penicillin, and reduced risks for osteoarthrosis and osteoarthritis. In conclusion, supplementation of calcium in individuals from the general population is not predicted to influence the risk of most investigated diseases to date. Moreover, long-term high serum calcium concentrations may result in adverse health outcomes. © 2021 The Authors. JBMR Plus published by Wiley Periodicals LLC on behalf of American Society for Bone and Mineral Research.

Heterozygosity for a Pathogenic Variant in SLC12A3 That Causes Autosomal Recessive Gitelman Syndrome Is Associated with Lower Serum Potassium

BACKGROUND

Potassium levels regulate multiple physiologic processes. The heritability of serum potassium level is moderate, with published estimates varying from 17% to 60%, suggesting genetic influences. However, the genetic determinants of potassium levels are not generally known.

METHODS

A whole-exome sequencing association study of serum potassium levels in 5812 subjects of the Old Order Amish was performed. A dietary salt intervention in 533 Amish subjects estimated interaction between p.R642G and sodium intake.

RESULTS

A cluster of variants, spanning approximately 537 kb on chromosome 16q13, was significantly associated with serum potassium levels. Among the associated variants, a known pathogenic variant of autosomal recessive Gitelman syndrome (p.R642G SLC12A3) was most likely causal; there were no homozygotes in our sample. Heterozygosity for p.R642G was also associated with lower chloride levels, but not with sodium levels. Notably, p.R642G showed a novel association with lower serum BUN levels. Heterozygotes for p.R642G had a two-fold higher rate of self-reported bone fractures and had higher resting heart rates on a low-salt diet compared with noncarriers.

CONCLUSIONS

This study provides evidence that heterozygosity for a pathogenic variant in SLC12A3 causing Gitelman syndrome, a canonically recessive disorder, contributes to serum potassium concentration. The findings provide insights into SLC12A3 biology and the effects of heterozygosity on electrolyte homeostasis and related subclinical phenotypes that may have implications for personalized medicine and nutrition.

Phosphate Metabolism in Health and Disease

Phosphorus, a 5A element with atomic weight of 31, comprises just over 0.6% of the composition by weight of plants and animals. Three isotopes are available for studying phosphorus metabolism and kinetics. ³¹P is stable, whereas the radioactive isotope ³³P has a half-life of 25 days and ³²P has a half-life of 14 days. Phosphate ester and phosphoanhydride are common chemical linkages and phosphorus is a key element in organic molecules involved in a wide variety of essential cellular functions. These include biochemical energy transfer via adenosine triphosphate (ATP), maintenance of genetic information with nucleotides DNA and RNA, intracellular signaling via cyclic adenosine monophosphate (cAMP), and membrane structural integrity via glycerophospholipids. However, this review focuses on the metabolism of inorganic phosphorus (Pi) acting as a weak acid. Phosphoric acid has all three hydrogens attached to oxygen and is a weak diprotic acid. It has 3 pKa values: pH 2.2, pH 7.2, and pH 12.7. At physiological pH of 7.4, Pi exists as both H₂PO₄^(-) and HPO₄^(2-) and acts as an extracellular fluid (ECF) buffer. Pi is the form transported across tissue compartments and cells. Measurement of Pi in biological fluids is based on its reaction with ammonium molybdate which does not measure organic phosphorus. In humans, 80% of the body phosphorus is present in the form of calcium phosphate crystals (apatite) that confer hardness to bone and teeth, and function as the major phosphorus reservoir (Fig. 1). The remainder is present in soft tissues and ECF. Dietary phosphorus, comprising both inorganic and organic forms, is digested in the upper gastrointestinal tract. Absorbed Pi is transported to and from bone, skeletal muscle and soft tissues, and kidney at rates determined by ECF Pi concentration, rate of blood flow, and activity of cell Pi transporters (Fig. 2). During growth, there is net accretion of phosphorus, and with aging, net loss of phosphorus occurs. The bone phosphorus reservoir is depleted and repleted by overall phosphorus requirement. Skeletal muscle is rich in phosphorus used in essential biochemical energy transfer. Kidney is the main regulator of ECF Pi concentration by virtue of having a tubular maximum reabsorptive capacity for Pi (TmPi) that is under close endocrine control. It is also the main excretory pathway for Pi surplus which is passed in urine. Transcellular and paracellular Pi transports are performed by a number of transport mechanisms widely distributed in tissues, and particularly important in gut, bone, and kidney. Pi transporters are regulated by a hormonal axis comprising fibroblast growth factor 23 (FGF23), parathyroid hormone (PTH), and 1,25 dihydroxy vitamin D (1,25D). Pi and calcium (Ca) metabolism are intimately interrelated, and clinically neither can be considered in isolation. Diseases of Pi metabolism affect bone as osteomalacia/rickets, soft tissues as ectopic mineralization, skeletal muscle as myopathy, and kidney as nephrocalcinosis and urinary stone formation. Fig. 1 Content of phosphorus in human adult: skeleton, soft tissue, and extracellular fluid (grams, log scale). Corresponding data for calcium are shown for comparison Fig. 2 Phosphate (Pi) transport to and from tissue compartments in mg/24 h. At a dietary phosphorus of 1400 mg, 1120 mg is absorbed in upper intestine to the ECF, 210 mg returned to intestine by endogenous secretion, resulting in 910 mg net Pi absorption and 490 mg fecal excretion. At bone, 180 mg is deposited by bone formation and 180 mg return to the ECF by bone resorption. At kidney, 5040 mg is filtered at the glomerulus and 4130 mg return to the ECF by tubular reabsorption with 910 mg excreted in the urine. In soft tissue, Pi is exchanged between ECF and cells.

Familial Aggregation of CKD and Heritability of Kidney Biomarkers in the General Population: The Lifelines Cohort Study

RATIONALE & OBJECTIVE

Chronic kidney disease (CKD) has a heritable component. We aimed to quantify familial aggregation of CKD in the general population and assess the extent to which kidney traits could be explained by genetic and environmental factors.

STUDY DESIGN

Cross-sectional 3-generation family study.

SETTING & PARTICIPANTS

Data were collected at entry into the Lifelines Cohort Study from a sample of the general population of the northern Netherlands, composed predominantly of individuals of European ancestry.

EXPOSURE

Family history of CKD.

OUTCOMES

The primary outcome was CKD, defined as estimated glomerular filtration rate (eGFR)<60mL/min/1.73m², where GFR was estimated using the CKD Epidemiology Collaboration creatinine equation. Among a subsample for which urinary albumin concentration was available (n=59,943), urinary albumin excretion was expressed as the rate of urinary albumin excretion (UAE) per 24 hours or urinary albumin-creatinine ratio (UACR).

ANALYTICAL APPROACH

Familial aggregation of CKD was assessed by calculating the recurrence risk ratio (RRR), using adapted Cox proportional hazards models. Heritability of continuous kidney-related traits was estimated using linear mixed models and defined as the ratio of the additive genetic variance to total phenotypic variance. All models were adjusted for age, sex, and known risk factors for kidney disease.

RESULTS

Among 155,911 participants with available eGFR data, the prevalence of CKD was 1.19% (1,862 cases per 155,911). The risk of CKD in those with an affected first-degree relative was 3 timeshigher than the risk in the total sample (RRR, 3.04 [95% CI, 2.26-4.09). In those with an affected spouse, risk of CKD was also higher (RRR, 1.56 [95% CI, 1.20-1.96]), indicative of shared environmental factors and/or assortative mating. Heritability estimates of eGFR, UAE, and UACR were 44%, 20%, and 18%, respectively. For serum urea, creatinine, and uric acid, estimates were 31%, 37%, and 48%, respectively, whereas estimates for serum electrolytes ranged from 22% to 28%.

LIMITATIONS

Use of estimated rather than measured GFR. UAE data only available in a subsample.

CONCLUSIONS

In this large population-based family study, a positive family history was strongly associated with increased risk of CKD. We observed moderate to high heritability of kidney traits and related biomarkers. These results indicate an important role of genetic factors in CKD risk.

A critical evaluation of results from genome-wide association studies of micronutrient status and their utility in the practice of precision nutrition

Rapid advances in ‘omics’ technologies have paved the way forward to an era where more ‘precise’ approaches – ‘precision’ nutrition – which leverage data on genetic variability alongside the traditional indices, have been put forth as the state-of-the-art solution to redress the effects of malnutrition across the life course. We purport that this inference is premature and that it is imperative to first review and critique the existing evidence from large-scale epidemiological findings. We set out to provide a critical evaluation of findings from genome-wide association studies (GWAS) in the roadmap to precision nutrition, focusing on GWAS of micronutrient disposition. We found that a large number of loci associated with biomarkers of micronutrient status have been identified. Mean estimates of heritability of micronutrient status ranged between 20 and 35 % for minerals, 56–59 % for water-soluble and 30–70 % for fat-soluble vitamins. With some exceptions, the majority of the identified genetic variants explained little of the overall variance in status for each micronutrient, ranging between 1·3 and 8 % (minerals), <0·1–12 % (water-soluble) and 1·7–2·3 % for (fat-soluble) vitamins. However, GWAS have provided some novel insight into mechanisms that underpin variability in micronutrient status. Our findings highlight obvious gaps that need to be addressed if the full scope of precision nutrition is ever to be realised, including research aimed at (i) dissecting the genetic basis of micronutrient deficiencies or ‘response’ to intake/supplementation (ii) identifying trans-ethnic and ethnic-specific effects (iii) identifying gene–nutrient interactions for the purpose of unravelling molecular ‘behaviour’ in a range of environmental contexts.

Heritability and individuality of the plasma sodium concentration: a twin study in the United States veteran population

Little is known about the population genetics of water balance. A recent meta-genome-wide association study on plasma sodium concentration identified novel loci of high biological plausibility, yet heritability of the phenotype has never been convincingly shown in European ancestry. The present study linked the Vietnam Era Twin Registry with the Department of Veterans Affairs VistA patient care clinical database. Participants (n = 2,370, 59.6% monozygotic twins and 40.4% dizygotic twins) had a median of seven (interquartile range: 3-14) plasma sodium determinations between October 1999 and March 2017. Heritability of the mean plasma sodium concentration among all twins was 0.41 (95% confidence interval: 0.35-0.46) and 0.49 (95% confidence interval: 0.43-0.54) after exclusion of 514 twins with only a single plasma sodium determination. Heritability among Caucasian (n = 1,958) and African-American (n = 268) twins was 0.41 (95% confidence interval: 0.34-0.47) and 0.36 (95% confidence interval: 0.17-0.52), respectively. Exclusion of data from twins who had been prescribed medications known to impact systemic water balance had no effect. The ability of the present study to newly detect substantial heritability across multiple racial groups was potentially a function of the cohort size and relatedness, exclusion of sodium determinations confounded by elevated plasma glucose and/or reduced glomerular filtration rate, transformation of plasma sodium for the independent osmotic effect of plasma glucose, and use of multiple laboratory determinations per individual over a period of years. Individual-level plasma sodium concentration exhibited longitudinal stability (i.e., individuality); the degree to which individual-level means differed from the population mean was substantial, irrespective of the number of determinations. In aggregate, these data establish the heritability of plasma sodium concentration in European ancestry and corroborate its individuality.

Heritable traits that contribute to nephrolithiasis

Urinary stones tend to cluster in families. Of the known risk factors, evidence is strongest for heritability of urinary calcium excretion. Recent studies suggest that other stone risk factors may have heritable components including urinary pH, citrate and magnesium excretion, and circulating vitamin D concentration. Several risk factors assumed purely environmental may also have heritable components, including dietary intake and thirst. Thus, future studies may reveal that genetics plays an even stronger role in urinary stone pathogenesis than previously known.

A Mendelian randomization study of the effect of calcium on coronary artery disease, myocardial infarction and their risk factors

Meta-analyses of randomized controlled trials (RCTs) suggest calcium could have adverse effects on cardiovascular disease, although these findings are controversial. To clarify, we assessed whether people with genetically higher calcium had a higher risk of coronary artery disease (CAD), myocardial infarction (MI) and their risk factors. We used a two-sample Mendelian randomization study. We identified genetic variants (single nucleotide polymorphisms (SNPs)) that independently contributed to serum calcium at genome-wide significance which we applied to large extensively genotyped studies of CAD, MI, diabetes, lipids, glycaemic traits and adiposity to obtain unconfounded estimates, with body mass index (BMI) as a control outcome. Based on 4 SNPs each 1 mg/dl increase in calcium was positively associated with CAD (odds ratio (OR) 1.49, 95% confidence interval (CI) 1.02–2.17), MI (OR 1.58, 95% CI 1.06–2.35), LDL-cholesterol (0.21 standard deviations, 95% CI 0.01–0.4), total cholesterol (0.21 standard deviations, 95% CI 0.03-0.38) and possibly triglycerides (0.19 standard deviations, 95% CI −0.1–0.48), but was unlikely related to BMI although the estimate lacked precision. Sensitivity analysis using 13 SNPs showed a higher risk for CAD (OR 1.87, 95% CI 1.14–3.08). Our findings, largely consistent with the experimental evidence, suggest higher serum calcium may increase the risk of CAD.

Genome-wide association study of serum minerals levels in children of different ethnic background

Calcium, magnesium, potassium, sodium, chloride and phosphorus are the major dietary minerals involved in various biological functions and are commonly measured in the blood serum. Sufficient mineral intake is especially important for children due to their rapid growth. Currently, the genetic mechanisms influencing serum mineral levels are poorly understood, especially for children. We carried out a genome-wide association (GWA) study on 5,602 European-American children and 4,706 African-American children who had mineral measures available in their electronic medical records (EMR). While no locus met the criteria for genome-wide significant association, our results demonstrated a nominal association of total serum calcium levels with a missense variant in the calcium –sensing receptor (CASR) gene on 3q13 (rs1801725, P = 1.96 × 10^-3) in the African-American pediatric cohort, a locus previously reported in Caucasians. We also confirmed the association result in our pediatric European-American cohort (P = 1.38 × 10^-4). We further replicated two other loci associated with serum calcium levels in the European-American cohort (rs780094, GCKR, P = 4.26 × 10^-3; rs10491003, GATA3, P = 0.02). In addition, we replicated a previously reported locus on 1q21, demonstrating association of serum magnesium levels with MUC1 (rs4072037, P = 2.04 × 10^-6). Moreover, in an extended gene-based association analysis we uncovered evidence for association of calcium levels with the previously reported gene locus DGKD in both European-American children and African-American children. Taken together, our results support a role for CASR and DGKD mediated calcium regulation in both African-American and European-American children, and corroborate the association of calcium levels with GCKR and GATA3, and the association of magnesium levels with MUC1 in the European-American children.

Meta-analysis of genome-wide association studies identifies six new Loci for serum calcium concentrations

Calcium is vital to the normal functioning of multiple organ systems and its serum concentration is tightly regulated. Apart from CASR, the genes associated with serum calcium are largely unknown. We conducted a genome-wide association meta-analysis of 39,400 individuals from 17 population-based cohorts and investigated the 14 most strongly associated loci in ≤ 21,679 additional individuals. Seven loci (six new regions) in association with serum calcium were identified and replicated. Rs1570669 near CYP24A1 (P = 9.1E-12), rs10491003 upstream of GATA3 (P = 4.8E-09) and rs7481584 in CARS (P = 1.2E-10) implicate regions involved in Mendelian calcemic disorders: Rs1550532 in DGKD (P = 8.2E-11), also associated with bone density, and rs7336933 near DGKH/KIAA0564 (P = 9.1E-10) are near genes that encode distinct isoforms of diacylglycerol kinase. Rs780094 is in GCKR. We characterized the expression of these genes in gut, kidney, and bone, and demonstrate modulation of gene expression in bone in response to dietary calcium in mice. Our results shed new light on the genetics of calcium homeostasis.

F, Glazer N, Kapur K, Kema I, Lopez L, Schillert A, Smith A, Winkler C, Zgaga L, Bandinelli S, Bergmann S, Boban M, Bochud M, Chen Y, Davies G, Dehghan A, Ding J, Doering A, Durda J, Ferrucci L, Franco O, Franke L, Gunjaca G, Hofman A, Hsu FC, Kolcic I, Kraja A, Kubo M, Lackner K, Launer L, Loehr L, Li G, Meisinger C, Nakamura Y, Schwienbacher C, Starr J, Takahashi A, Torlak V, Uitterlinden A, Vitart V, Waldenberger M, Wild P, Kirin M, Zeller T, Zemunik T, Zhang Q, Ziegler A, Blankenberg S, Boerwinkle E, Borecki I, Campbell H, Deary I, Frayling T, Gieger C, Harris T, Hicks A, Koenig W, O’Donnell C, Fox C, Pramstaller P, Psaty B, Reiner A, Rotter J, Rudan I, Snieder H, Tanaka T, van Duijn C, Vollenweider P, Waeber G, Wilson J, Witteman J, Wolffenbuttel B, Wright A, Wu Q, Liu Y, Jenny N, North K, Felix J, Alizadeh B, Cupples L, Perry J, Morris A. Discovery and fine mapping of serum protein loci through transethnic meta-analysis

Many disorders are associated with altered serum protein concentrations, including malnutrition, cancer, and cardiovascular, kidney, and inflammatory diseases. Although these protein concentrations are highly heritable, relatively little is known about their underlying genetic determinants. Through transethnic meta-analysis of European-ancestry and Japanese genome-wide association studies, we identified six loci at genome-wide significance (p < 5 × 10(-8)) for serum albumin (HPN-SCN1B, GCKR-FNDC4, SERPINF2-WDR81, TNFRSF11A-ZCCHC2, FRMD5-WDR76, and RPS11-FCGRT, in up to 53,190 European-ancestry and 9,380 Japanese individuals) and three loci for total protein (TNFRS13B, 6q21.3, and ELL2, in up to 25,539 European-ancestry and 10,168 Japanese individuals). We observed little evidence of heterogeneity in allelic effects at these loci between groups of European and Japanese ancestry but obtained substantial improvements in the resolution of fine mapping of potential causal variants by leveraging transethnic differences in the distribution of linkage disequilibrium. We demonstrated a functional role for the most strongly associated serum albumin locus, HPN, for which Hpn knockout mice manifest low plasma albumin concentrations. Other loci associated with serum albumin harbor genes related to ribosome function, protein translation, and proteasomal degradation, whereas those associated with serum total protein include genes related to immune function. Our results highlight the advantages of transethnic meta-analysis for the discovery and fine mapping of complex trait loci and have provided initial insights into the underlying genetic architecture of serum protein concentrations and their association with human disease.

Heritability of serum sodium concentration: evidence for sex- and ethnic-specific effects

Serum sodium concentration is the clinical index of systemic water balance. Although disordered water balance is common and morbid, little is known about genetic effects on serum sodium concentration at the population level. Prior studies addressed only participants of European descent and either failed to demonstrate significant heritability or showed only modest effect. We investigated heritability of serum sodium concentration in large cohorts reflecting a range of races/ethnicities, including the Framingham Heart Study (FHS, non-Hispanic Caucasian), the Heredity and Phenotype Intervention Heart Study (HAPI, Amish Caucasian), the Jackson Heart Study (JHS, African American), the Strong Heart Family Study (SHFS, American Indian), and the Genetics of Kidney Disease in Zuni Indians Study (GKDZI, American Indian). Serum sodium was transformed for the osmotic effect of glucose, and participants with markedly elevated glucose or reduced estimated glomerular filtration rate (eGFR) were excluded. Using a standard variance components method, incorporating covariates of age, glucose, and eGFR, we found heritability to be high in African American and American Indian populations and much more modest in non-Hispanic Caucasian populations. Estimates among females increased after stratification on sex and were suggestive among female participants in FHS (0.18 ± 0.12, P = 0.057) and male participants in JHS (0.24 ± 0.16, P = 0.067) and statistically significant among female participants in JHS (0.44 ± 0.09, P = 1 × 10 ⁻⁷), SHFS (0.59 ± 0.05, P = 9.4 × 10⁻⁴⁶), and GKDZI (0.46 ± 0.15, P = 1.7 × 10⁻⁴), and male participants in HAPI (0.18 ± 0.12, P = 0.03) and SHFS (0.67 ± 0.07, P = 5.4 × 10⁻²⁶). Exclusion of diuretic users increased heritability among females and was significant in all cohorts where data were available. In aggregate, these data strongly support the heritability of systemic water balance and underscore sex and ethnicity-specific effects.

Common variants in the calcium-sensing receptor gene are associated with total serum calcium levels

Serum calcium levels are tightly regulated. We performed genome-wide association studies (GWAS) in population-based studies participating in the CHARGE Consortium to uncover common genetic variations associated with total serum calcium levels. GWAS of serum calcium concentrations was performed in 20 611 individuals of European ancestry for ∼2.5 million genotyped and imputed single-nucleotide polymorphisms (SNPs). The SNP with the lowest P-value was rs17251221 (P = 2.4 * 10(-22), minor allele frequency 14%) in the calcium-sensing receptor gene (CASR). This lead SNP was associated with higher serum calcium levels [0.06 mg/dl (0.015 mmol/l) per copy of the minor G allele] and accounted for 0.54% of the variance in serum calcium concentrations. The identification of variation in CASR that influences serum calcium concentration confirms the results of earlier candidate gene studies. The G allele of rs17251221 was also associated with higher serum magnesium levels (P = 1.2 * 10(-3)), lower serum phosphate levels (P = 2.8 * 10(-7)) and lower bone mineral density at the lumbar spine (P = 0.038), but not the femoral neck. No additional genomic loci contained SNPs associated at genome-wide significance (P < 5 * 10(-8)). These associations resemble clinical characteristics of patients with familial hypocalciuric hypercalcemia, an autosomal-dominant disease arising from rare inactivating mutations in the CASR gene. We conclude that common genetic variation in the CASR gene is associated with similar but milder features in the general population.

Genome-wide meta-analysis for serum calcium identifies significantly associated SNPs near the calcium-sensing receptor (CASR) gene

Calcium has a pivotal role in biological functions, and serum calcium levels have been associated with numerous disorders of bone and mineral metabolism, as well as with cardiovascular mortality. Here we report results from a genome-wide association study of serum calcium, integrating data from four independent cohorts including a total of 12,865 individuals of European and Indian Asian descent. Our meta-analysis shows that serum calcium is associated with SNPs in or near the calcium-sensing receptor (CASR) gene on 3q13. The top hit with a p-value of 6.3×10^-37 is rs1801725, a missense variant, explaining 1.26% of the variance in serum calcium. This SNP had the strongest association in individuals of European descent, while for individuals of Indian Asian descent the top hit was rs17251221 (p = 1.1×10^-21), a SNP in strong linkage disequilibrium with rs1801725. The strongest locus in CASR was shown to replicate in an independent Icelandic cohort of 4,126 individuals (p = 1.02×10^-4). This genome-wide meta-analysis shows that common CASR variants modulate serum calcium levels in the adult general population, which confirms previous results in some candidate gene studies of the CASR locus. This study highlights the key role of CASR in calcium regulation.

Calcium levels in blood serum play an important role in many biological processes. The regulation of serum calcium is under strong genetic control. This study describes the first meta-analysis of a genome-wide association study from four cohorts totaling 12,865 participants of European and Indian Asian descent. Confirming previous results in some candidate gene studies, we find that common polymorphisms at the calcium-sensing receptor (CASR) gene locus are associated with serum calcium concentrations. We show that CASR variants give rise to the strongest signals associated with serum calcium levels in both European and Indian Asian populations, while no other locus reaches genome-wide significance. Our results show that CASR is a key player in genetic regulation of serum calcium in the adult general population.

A meta-analysis of genome-wide data from five European isolates reveals an association of COL22A1, SYT1, and GABRR2 with serum creatinine level

BACKGROUND

Serum creatinine (S CR) is the most important biomarker for a quick and non-invasive assessment of kidney function in population-based surveys. A substantial proportion of the inter-individual variability in S CR level is explicable by genetic factors.

METHODS

We performed a meta-analysis of genome-wide association studies of S CR undertaken in five population isolates ('discovery cohorts'), all of which are part of the European Special Population Network (EUROSPAN) project. Genes showing the strongest evidence for an association with SCR (candidate loci) were replicated in two additional population-based samples ('replication cohorts').

RESULTS

After the discovery meta-analysis, 29 loci were selected for replication. Association between SCR level and polymorphisms in the collagen type XXII alpha 1 (COL22A1) gene, on chromosome 8, and in the synaptotagmin-1 (SYT1) gene, on chromosome 12, were successfully replicated in the replication cohorts (p value = 1.0 x 10(-6) and 1.7 x 10(-4), respectively). Evidence of association was also found for polymorphisms in a locus including the gamma-aminobutyric acid receptor rho-2 (GABRR2) gene and the ubiquitin-conjugating enzyme E2-J1 (UBE2J1) gene (replication p value = 3.6 x 10(-3)). Previously reported findings, associating glomerular filtration rate with SNPs in the uromodulin (UMOD) gene and in the schroom family member 3 (SCHROOM3) gene were also replicated.

CONCLUSIONS

While confirming earlier results, our study provides new insights in the understanding of the genetic basis of serum creatinine regulatory processes. In particular, the association with the genes SYT1 and GABRR2 corroborate previous findings that highlighted a possible role of the neurotransmitters GABAA receptors in the regulation of the glomerular basement membrane and a possible interaction between GABAA receptors and synaptotagmin-I at the podocyte level.

Determinants of kidney function in Swedish families: role of heritable factors

The aim of this study was to evaluate the determinants of kidney function and the role of heritable factors in a sample of 249 siblings free from known cardiovascular disease and without antihypertensive drugs belonging to 110 families. Four different measures and estimates of kidney function were considered. Blood pressure was recorded during 24 h by ambulatory blood pressure monitoring. Heritability was estimated with and without adjustment for significant covariates.In multivariate analysis, in addition to age, sex, BMI, HDL-cholesterol, 24-h systolic and mean blood pressure, systolic nocturnal blood pressure dipping resulted independently related to serum creatinine, estimated Cockcroft-Gault-creatinine clearance and estimated by the modification of diet in renal disease-glomerular filtration rate. After full adjustment, the heritability values were 51% for the measured creatinine clearance (P < 0.01), 58% for the estimated Cockcroft-Gault-creatinine clearance (P < 0.001), 40% for the estimated by the modification of diet in renal disease-glomerular filtration rate (P < 0.001), but 8% (P = 0.34) for serum creatinine.Our data confirm that kidney function is partially under genetic control and that genetic variants of importance for this trait could be mapped. The association of the circadian rhythm of blood pressure with kidney function in this sample deserves further investigation.

Linkage analysis of glomerular filtration rate in American Indians

American Indians have a disproportionately high rate of kidney disease likely due to a combination of environmental and genetic factors. We performed a genome wide scan of estimated glomerular filtration rate in 3665 participants of the Strong Heart Family Study to localize genes influencing kidney disease risk factors. The participants were men and women from 13 American Indian tribes recruited from 3 centers located in Arizona, the Dakotas and Oklahoma. Multipoint variance component linkage analysis was performed for each center and on the entire cohort after controlling for center effects. Modeling strategies that incorporated age, gender and interaction terms (model 1) and another that also controlled for diabetes mellitus, systolic and diastolic blood pressure, body mass index, low density and high density lipoproteins, triglycerides and smoking status (model 2) were used. Significant evidence for linkage in the Arizona group was found on chromosome 12p12.2 at 39cM (nearest marker D12S310) using model 1. Additional loci with very suggestive evidence for linkage were detected at 1p36.31 for all groups using both models and at 2q33.3 and 9q34.2 for the Dakotas group each using model 1. No significant evidence for additive interaction with diabetes, hypertension or obesity was noted. This evidence for linkage of a quantitative trait locus influencing estimated glomerular filtration rate to a region of chromosome 12p in a large cohort of American Indians will be worth studying in more detail in the future.

Plasma potassium level is associated with common genetic variation in the beta-subunit of the epithelial sodium channel

Plasma potassium is a moderately heritable phenotype, but no robust associations between common single nucleotide polymorphisms (SNPs) and plasma potassium have previously been described. Genetic influences on renal potassium handling could be important in the etiology of hypertension. We have tested whether common genetic variation in the gene encoding the beta-subunit of the epithelial sodium channel (SCNN1B) affects plasma potassium and blood pressure level in a study of 1,425 members of 248 families ascertained on a proband with hypertension. We characterized family members for blood pressure using ambulatory monitoring, measured plasma potassium in venous blood samples, and genotyped four SNPs that spanned the SCNN1B gene. We found highly significant association between genotype at the SCNN1B rs889299 SNP situated in intron 4 of the gene and plasma potassium. Homozygotes for the rarer T allele had on average a 0.15 mM lower plasma potassium than homozygotes for the common C allele, with an intermediate value for heterozygotes (trend, P = 0.0003). Genotype at rs889299 accounted for approximately 1% of the total variability in plasma potassium, or around 3% of the total heritable fraction. There was no association between genotype at any SCNN1B SNP and blood pressure considered as a quantitative trait, or with hypertension affection status. We have shown a modest sized but highly significant effect of common genetic variation in the SCNN1B gene on plasma potassium. Interaction between the rs889299 SNP and functional SNPs in other genes influencing aldosterone-responsive distal tubular electrolyte transport may be important in the etiology of essential hypertension.

Primary hyperparathyroidism and the presence of kidney stones are associated with different haplotypes of the calcium-sensing receptor

INTRODUCTION

Three single-nucleotide polymorphisms in the calcium-sensing receptor gene (CASR) encoding the missense substitutions A986S, R990G, and Q1011E have been associated with normal variation in extracellular calcium homeostasis, both individually and in haplotype combination. The aim of this study was to examine haplotype associations in primary hyperparathyroidism (PHPT).

PATIENTS AND METHODS

Patients with sporadic PHPT (n = 237) were recruited from endocrine clinics and healthy controls (n = 433) from a blood donor clinic, and levels of serum calcium, albumin, and PTH were measured. In PHPT patients, urinary calcium/creatinine clearances and bone mineral density at spine and femoral neck were measured and the presence of kidney stones and vertebral fractures identified. The CASR single-nucleotide polymorphisms were haplotyped by allele-specific sequencing.

RESULTS

Four haplotypes (ARQ, SRQ, AGQ, and ARE) of eight were observed, in keeping with significant linkage disequilibrium, but haplotype frequencies did not show significant Hardy-Weinberg disequilibrium. The SRQ haplotype was more common in PHPT (125 of 474 alleles) than in controls (170 of 866 alleles, P = 0.006) and showed a significant (P = 0.006) gene-dosage effect. There was no significant association between haplotype and bone mineral density or fractures, but association with kidney stones was significant (P = 0.0007). In the stone-forming subgroup, the SRQ haplotype was underrepresented and AGQ overrepresented. Patients bearing the AGQ haplotype had an odds ratio of 3.8 (95% confidence interval, 1.30-11.3) for presentation with renal stones compared with the rest.

CONCLUSION

Our data indicate that the CASR SRQ haplotype is significantly associated with PHPT in our population. Within the PHPT patient population, the AGQ haplotype is significantly associated with kidney stones.

Heritable Components of Feline Hematology, Clinical Chemistry, and Acid–Base Profiles

Four erythrocyte variables (erythrocyte count, hemoglobin, mean cell volume, packed cell volume), 14 serum variables (alanine transferase, albumin, alkaline phosphatase, calcium, chloride, cholesterol, creatinine, glucose, phosphorus, potassium, sodium, total protein, triglycerides, urea nitrogen), and 7 venous acid-base variables (base excess, bicarbonate, carbon dioxide partial pressure, oxygen partial pressure, oxygen saturation, pH, and total carbon dioxide) were evaluated for heritability in domestic cats (Felis catus). Values used for individual cats were expressed as the mean over all lifetime measurements, using 444-530 animals for clinical chemistry, 629 animals for acid-base, and 564 animals for erythrocyte metrics. Gender and age at death (where applicable) also were evaluated for correlation with variables. Heritabilities for clinical chemistry, acid-base, and erythrocyte variables ranged, respectively, from 0.13 to 0.78, from 0.23 to 0.59, and from 0.41 to 0.69 (P < 0.05). This result indicates that serum variability has a genetic basis and is segregating in this feline population. These findings may have important implications in both research and clinical medicine.

Genomewide linkage analysis of soluble transferrin receptor plasma levels

Genetic control of soluble transferrin receptor (sTfR) levels was demonstrated using family-based studies (GAIT, Genetic Analysis of Idiopathic Thrombophilia project); moreover, a genetic relationship was observed between sTfR and the risk for thrombosis, suggesting that these phenotypes shared genetic determinants. We studied the regions that control sTfR. To assess such regions, a full genome scan was carried out using 604 highly polymorphic deoxyribonucleic acid markers (resolution 7.3 cM) in 21 extended pedigrees (358 individuals). Then, a quantitative trait linkage analysis was performed using variance components methods. The genomewide scan linkage analysis showed two regions (quantitative trait locus or QTL) with significant limit of detection (LOD) scores (2q23.14, LOD score = 2.64, nominal p = 0.00024; 3q21.2, LOD score = 1.94, nominal p = 0.0014). There were no obvious candidate genes in these regions. In conclusion, this linkage analysis suggested the existence of a QTL in 2q23.14 that probably harbored a gene (or genes) controlling sTfR levels. Moreover, a second linkage signal was observed in 3q21.2; albeit the evidence for this second locus was lower. The next step will be to identify the gene(s) and its possible involvement in thrombosis and iron homeostasis.

Heritability of biochemical kidney markers and relation to survival in the elderly--results from a Danish population-based twin study

BACKGROUND AND AIM

We performed a twin study to assess the relative contribution of genetic and environmental factors to serum levels of urea, creatinine, urate and sodium in a population of 688 elderly twins (73-95 years). Furthermore, we tested the association between these biochemical values and mortality to examine the consequence of an abnormal biochemical kidney parameter in an aging population.

RESULTS

A third to a half of the variation in the biochemical kidney tests is due to genetic factors except for creatinine in males. Survival analysis show that all four parameters influence mortality and values below reference interval for urea and urate have a more pronounced impact on survival [hazard ratios (95% confidence interval): 2.32 (1.03-5.26) and 3.56 (1.46-8.69), respectively] than values above [1.20 (0.87-1.64) and 1.50 (1.11-2.02), respectively]. Increased creatinine (above 130 micromol/l) and decreased sodium (below 136 mmol/l) also have a significant impact on survival with hazard ratios on 1.83 (1.13-2.95) and 1.56 (1.22-1.99), respectively. Between 5% and 44% of the measured values are outside the established reference interval.

CONCLUSION

This study provides evidence for the importance of genetic factors in determining the biochemical kidney parameters in an aging population. Furthermore, our data shows that abnormal kidney parameters are common in older adults and results in a significant increase in mortality risk.

Blood ionized calcium is associated with clustered polymorphisms in the carboxyl-terminal tail of the calcium-sensing receptor

Blood ionized calcium (iCa) is a quantitative trait subject to genetic influence. iCa is maintained in a narrow range through the action of the calcium-sensing receptor (CASR) controlling PTH secretion and calcium excretion. A CASR single nucleotide polymorphism (SNP) prevalent in Caucasian populations (A986S) has shown significant association with iCa in a cohort of young women, but association with the neighboring SNPs, R990G and Q1011E, has not been examined. We studied 377 unrelated adults (184 men and 193 women) recruited as healthy adults from a blood donor clinic. The subjects were not taking any medications, nor did they have disorders of calcium metabolism. Relative frequencies for the CASR 986S, 990G, and 1011E minor alleles were 24%, 4%, and 3% respectively. At the A986S locus, subjects with the AA genotype had significantly lower iCa (P = 0.0001) than subjects with one or two S alleles (mean +/- se, 1.221 +/- 0.003 vs. 1.239 +/- 0.003 mmol/liter). For the R990G site, subjects with the RR genotype had higher iCa than those with one copy of the 990G allele (1.230 +/- 0.002 vs. 1.213 +/- 0.007 mmol/liter; P = 0.032). With respect to the 1011 locus, iCa was lower in QQ genotype subjects than in the QE group (1.227 +/- 0.002 vs. 1.255 +/- 0.008 mmol/liter; P = 0.002). After resolution of phase for the doubly heterozygous subjects, analysis was conducted on haplotypes across all three loci. As expected, subjects with SRQ and ARE haplotypes are relatively hypercalcemic, and those with AGQ are hypocalcemic, relative to subjects with the common ARQ haplotype. Multiple regression analysis with clinical covariates (age, sex and menopausal status, creatinine, and PTH) showed that 16.5% of the total variance in iCa may be explained, and the seven CASR haplotypes contribute significantly (P < 0.0001) and substantially (49.1% of the explained variance) to the model, with the following corrected iCa means: ARQ/AGQ, 1.21 +/- 0.01; ARQ/ARQ, 1.22 +/- 0.01; ARQ/SRQ, 1.24 +/- 0.01; SRQ/AGQ, 1.24 +/- 0.03; SRQ/SRQ, 1.25 +/- 0.01; ARQ/ARE, 1.25 +/- 0.01; and SRQ/ARE, 1.27 +/- 0.01. Our data confirm the association between iCa and the A986S locus and suggest that R990G and Q1011E are also predictive. Given the significant between-population variations in frequency of variant alleles in this CASR SNP cluster, tri-locus haplotyping may prove to be more informative in studies of association between variation in CASR and disease.

Familial and genetic determinants of systemic markers of inflammation: the NHLBI family heart study

Inflammation is thought to play a central role in the etiology and outcome of atherosclerosis. Animal studies as well as in vitro and in vivo human studies suggest that host factors modulate the magnitude and extent of inflammatory responses. We investigated familial aggregation of three systemic markers of inflammation (C-reactive protein (CRP), white blood cell count (WBC), and albumin) in a large, cross-sectional study conducted in four US communities. We found evidence of substantial heritability (35-40%) for CRP levels as well as for WBC and albumin levels. Negligible spouse correlations suggested little influence of shared household environment on these traits. The combination of sociodemographic factors (age, center, education), behavioral and lifestyle factors (cigarette smoking, alcohol intake, hormone replacement therapy), obesity and fat patterning, and prevalent diabetes explained 13-30% the interindividual variability of these traits. There was no evidence that these inflammation phenotypes were linked to a microsatellite marker in the interleukin-1 gene cluster on chromosome 2q, a region that includes several candidate genes for chronic inflammatory diseases. Our findings suggest that CRP levels, albumin levels, and WBC are determined at least partially by genetic factors. Further efforts to identify gene loci affecting these traits are warranted.

Association between total serum calcium and the A986S polymorphism of the calcium-sensing receptor gene

Serum calcium is under tight physiological control, but it is also a quantitative trait with substantial genetic regulation. Mutations of the CASR gene cause familial hypocalciuric hypercalcemia or autosomal dominant hypoparathyroidism, depending on whether they decrease or increase, respectively, ligand binding to the receptor protein. We described an association between ionized calcium and a common polymorphism (A986S) found in the cytoplasmic tail of this G protein-coupled receptor. We report here on an independent study of 387 healthy young women. Genotyping was performed by allele-specific amplification and serum chemistries were measured by automated clinical assay. Frequencies of SS, AS, and AA genotypes were 6, 107, and 274, respectively, yielding a 986S allele frequency of 15.4%. Mean total serum calcium (Ca(T)) was significantly higher in the SS (9.88 +/- 0.29 mg/dL, P = 0.015) and AS groups (9.45 +/- 0.05 mg/dL, P = 0.002), than in the AA group (9.23 +/- 0.04 mg/dL). In multiple regression modeling, the A986S genotype remained an independently significant predictor of Ca(T) (P < 0.0001) when serum albumin, globulin, inorganic phosphate, and creatinine covariates were included. These data are the first to show significant association between a common polymorphism and concentrations of a serum electrolyte. The A986S polymorphism is also a potential predisposing factor in disorders of bone and mineral metabolism.

A986S polymorphism of the calcium-sensing receptor and circulating calcium concentrations

BACKGROUND

The regulation of extracellular calcium concentration by parathyroid hormone is mediated by a calcium-sensing, G-protein-coupled cell-surface receptor (CASR). Mutations of the CASR gene alter the set-point for extracellular ionised calcium [Ca2+]o and cause familial hypercalcaemia or hypocalcaemia. The CASR missense polymorphism, A986S, is common in the general population and is, therefore, a prime candidate as a genetic determinant of extracellular calcium concentration.

METHODS

We genotyped the CASR A986S variant (S allele frequency of 16.3%) in 163 healthy adult women and tested samples of their serum for total calcium, albumin, total protein, creatinine, phosphate, pH, and parathyroid hormone. A prospectively generated, random subset of 84 of these women provided a whole blood sample for assay of [Ca2+]o.

FINDINGS

The A986S genotype showed no association with total serum concentration of calcium, until corrected for albumin. In a multivariate regression model, biochemical and genetic variables accounted for 74% of the total variation in calcium. The significant predictors of serum calcium were: albumin (p<0.001), phosphate (p=0.02), parathyroid hormone (p=0.007), pH (p=0.001), and A986S genotype (p=0.009). Fasting whole-blood [Ca2+]o also showed an independent positive association with the 986S variant (p=0.013).

INTERPRETATION

The CASR A986S variant has a significant effect on extracellular calcium. The CASR A986S polymorphism is a likely candidate locus for genetic predisposition to various bone and mineral disorders in which extracellular calcium concentrations have a prominent part.

Dementias: the role of magnesium deficiency and an hypothesis concerning the pathogenesis of Alzheimer's disease

Evidence is presented indicating that dementias are associated with a relative insufficiency of Magnesium (Mg) in the brain. Such insufficiency may be attributable to low intake or retention of Mg; high intake of a neurotoxic metal, such as aluminum (Al), which inhibits activity of Mg-requiring enzymes; or impaired transport of Mg and/or enhanced transport of the neurotoxic metal into brain tissue. It is proposed that Alzheimer's disease (AD) involves a defective transport process, characterized by both an abnormally high incorporation of Al and an abnormally low incorporation of Mg into brain neurons. The hypothesis is advanced that an altered serum protein contributes to the progression of AD by having a greater affinity for Al than for Mg, in contrast to the normal protein, which binds Mg better than Al. The altered protein crosses the blood-brain barrier more efficiently than the normal protein and competes with the normal protein in binding to brain neurons. Binding of the altered protein to the target neurons would both facilitate Al uptake and impede Mg uptake. Evidence suggests that albumin is the serum protein that is altered.

Heritability of clinical chemistries in an older twin cohort: the NHLBI Twin Study

Heritability analyses were performed with clinical chemistry data collected on 360 twin pairs of white, middle-aged male veterans during the second examination of the NHLBI Twin Study, a multicenter study of cardiovascular disease risk factors. Significant genetic variability was present for albumin, alkaline phosphatase, blood urea nitrogen, 1-hr postload glucose, phosphorus, total protein, and uric acid. Calcium and aspartate aminotransferase had significantly different means by zygosity, which precluded further analysis. Total bilirubin and lactate dehydrogenase did not show evidence for genetic variation at this examination. Comparisons are made to results from similar twin studies and the first examination of the NHLBI Twin Study. Heritability estimates for phosphorus and blood urea nitrogen exhibited marked stability across studies, while heritability estimates for total bilirubin, total protein, and uric acid decreased in older study populations. The heritability of 1-hr postload blood glucose decreased from 0.88 at the first NHLBI examination to 0.52 at the second one. Interpretation of these results requires consideration of possible selection biases, methodologic and demographic issues, and the view that for some clinical chemistries, biological aging along with prolonged environmental exposures may alter the amount of phenotypic variation explained by the additive effect of genes alone.

Blood pressure and chemistry: some correlations and apparent correlations

The reported correlation between plasma calcium and blood pressure has been investigated in 412 young men and women. In this sample, it seemed to be due to a stronger correlation between blood pressure and plasma albumin. Blood pressures were also significantly correlated with plasma high-density lipoprotein in men and with plasma uric acid in women.