Novel Positional and Biological Candidate Gene for Grip Strength in Older Adults: The Long Life Family Study

Grip strength is a robust indicator of overall health, is moderately heritable and predicts longevity in older adults. Using genome-wide linkage analysis, we identified a novel locus on chromosome 18p linked to grip strength in 4534 individuals from 582 families (age 70.0 ± 15.8, range 24–110 years; 54% women). DNA sequencing was completed to identify single nucleotide variants (SNVs) in the 3.44 – 4.04 mega-basepair region on chromosome 18p. Using the sequencing data, we performed association analyses between the 7312 SNVs in the region and grip strength in families exhibiting evidence for linkage. Models were adjusted for age, age2, sex, height, field center and population substructure. There were 23 families (263 individuals) that contributed to the linkage peak (cumulative logarithm of the odds [LOD] score = 12.4). Six families (112 individuals) accounted for most of the linkage signal (LOD = 6.4). In these 6 families, we found highly significant associations between SNVs in the Disks Large-associated Protein 1 (DLGAP1) gene and grip strength (lead SNV: β= -0.75kg ± 0.15, p-value= 4.3*10-6). Correcting for the top SNV in DLGAP1 reduces the LOD by 72% in these families. Further, the effect allele frequency is much higher in these 6 families (39.7%) compared with both the NHLBI’s Trans-OMICs for Precision Medicine (23.5%) and 1000Genomes (28.0%) references panels. The DLGAP1 gene plays an important role in post-synaptic density of neurons; thus, it is a novel positional and biological candidate gene for follow-up studies aimed at uncovering genetic determinants of muscle strength.

Linkage Guided Sequence Analysis Revealed a Novel Gene PKD1L2 for Adiponectin: The Long Life Family Study (LLFS)

Adiponectin is involved in regulating insulin resistance (IR) and is a potential regulator of healthy aging and lifespan. To identify novel variants associated with adiponectin, we further assessed our previously identified linkage peak on 16q23.2 (LODs=3.8). We used sequence data of 632 participants (age, 24-110 years) from 47 families of European ancestry in the Long Life Family Study, a study with familial clustering of exceptional longevity in the US and Denmark. Adiponectin levels were log-transformed, and adjusted for age, sex, sites, and PCs for ancestry. We found a variant in the PKD1L2 (rs527459046, p=2e-8, MAF=3%, r2=1.5%, accounting for linkage=28%). The PKD1L2, 1.4 Mb upstream of the CDH13 (adiponectin receptor gene) is expressed in heart, liver, and adipocytes, known to function as an ion-channel regulator or a GPCR regulator for aging-related lipolysis, IR, and adiponectin/leptin secretion. Haplotyping, epistatic and bioinformatic analyses will be engaged to capture additional/functional variants and regulatory networks.

Identification of a Novel Locus for Gait Speed Decline with Aging: The Long Life Family Study

Background Gait speed is a powerful indicator of health with aging. Potential genetic contributions to gait speed and its decline with aging are not well defined. We determined the heritability of and potential genetic regions underlying change in gait speed using longitudinal data from 2379 individuals belonging to 509 families in the Long Life Family Study (mean age 64±12, range 30–110 years; 45% men). Methods Gait-speed was measured over 4 meters at baseline and follow up (7±1 years). Quantitative trait linkage analyses were completed using pedigree-based maximum-likelihood methods with logarithm of the odds (LOD) scores >3.0 indicating genome-wide significance. We also performed linkage analysis in the top 10% of families contributing to LOD scores to allow for heterogeneity among families (HLOD). Data were adjusted for age, sex, height, and field center. Results At baseline, 26.9% of individuals had “slow” gait-speed <1.0 m/s (mean: 1.1±0.2 m/s) and gait speed declined at a rate of -0.02±0.03 m/s per year (p<0.0001). Baseline and change in gait-speed were significantly heritable (h 2 = 0.24-0.32, p<0.05). We did not find significant evidence for linkage for baseline gait speed; however, we identified a significant locus for change in gait speed on chromosome 16p (LOD=4.2). A subset of 21 families contributed to this linkage peak (HLOD = 6.83). Association analyses on chromosome 16 showed that the strongest variant resides within the ADCY9 gene. Conclusion Further analysis of the chromosome 16 region, and ADCY9 gene, may yield new insight on the biology of mobility decline with aging.

Genome-Wide Linkage Analysis Identifies a Novel Locus for Grip Strength: The Long Life Family Study

Grip strength declines with aging, is an indicator of overall health, and predicts mortality among older adults. Herein, we quantified the genetic contributions to grip strength among 4534 individuals, belonging to 574 families in the Long Life Family Study (age 70.3 ± 15.7, range 24–110 years; 56% women). Grip strength was measured using a handheld dynamometer, and the maximum value of two trials in the stronger hand was used. Quantitative trait linkage analysis was completed using pedigree-based maximum-likelihood methods with logarithm of the odds (LOD) scores >3.0 indicating genome-wide significance. Linkage analysis in the top 10% of families contributing to LOD scores was also performed to allow for heterogeneity among families (HLOD). All analyses were adjusted for age, sex, height and field center. Grip strength was lower per one year of older age (β: -0.34 ± 0.01kg, p <0.01), and overall: 24.3% of men and 19.3% of women had “low” grip strength according to European Working Group on Sarcopenia definitions. Grip strength was highly heritable (h2 = 0.37, p<0.05). We identified a potentially novel locus for grip strength on chromosome 18p (LOD 3.18) with 26 families contributing to this linkage peak (HLOD = 10.94). Deep sequencing of the chromosome 18 region may yield fundamental insight on the biology of muscle weakness with aging, and may help identify novel therapeutic targets for treatment and prevention of this common condition.

Clinical and pathologic phenotype of a large family with heterozygous STUB1 mutation

ObjectiveTo describe the clinical and pathologic features of a novel pedigree with heterozygous STUB1 mutation causing SCA48.MethodsWe report a large pedigree of Dutch decent. Clinical and pathologic data were reviewed, and genetic analyses (whole-exome sequencing, whole-genome sequencing, and linkage analysis) were performed on multiple family members.ResultsPatients presented with adult-onset gait disturbance (ataxia or parkinsonism), combined with prominent cognitive decline and behavioral changes. Whole-exome sequencing identified a novel heterozygous frameshift variant c.731_732delGC (p.C244Yfs*24) in STUB1 segregating with the disease. This variant was present in a linkage peak on chromosome 16p13.3. Neuropathologic examination of 3 cases revealed a consistent pattern of ubiquitin/p62-positive neuronal inclusions in the cerebellum, neocortex, and brainstem. In addition, tau pathology was present in 1 case.ConclusionsThis study confirms previous findings of heterozygous STUB1 mutations as the cause of SCA48 and highlights its prominent cognitive involvement, besides cerebellar ataxia and movement disorders as cardinal features. The presence of intranuclear inclusions is a pathologic hallmark of the disease. Future studies will provide more insight into its pathologic heterogeneity.

GENOME-WIDE LINKAGE ANALYSIS IDENTIFIES A NOVEL LOCUS FOR LONGITUDINAL GAIT SPEED CHANGE WITH AGING

Gait speed is an indicator of health and function with aging. The potential genetic contributions to gait speed and its decline with aging are not well characterized. We sought to better quantify the genetic contributions to and identify potential genes and genetic variants underlying change in gait speed among older adults. To accomplish these aims, we used data from 2379 individuals belonging to 509 families in the Long Life Family Study (mean age 64 ± 12, range 30–110 years; 45% men). Gait-speed was measured over 4 meters at baseline and after an average of 7±1.1 years. Quantitative trait linkage analyses were completed using pedigree-based maximum-likelihood methods with logarithm of the odds (LOD) scores > 3.3 indicating genome-wide significance. We also performed linkage analysis in the top 10% of families contributing to LOD scores to allow for heterogeneity among families (HLOD). Data were adjusted for age, sex, height and field center. At baseline, 26.9% of individuals had “low” gait-speed <1.0 m/s (mean: 1.1±0.2 m/s) and gait speed declined at a rate of -0.02±0.03 m/s per year (p<0.0001). Baseline and change in gait-speed were significantly heritable (h2 = 0.24-0.32, p<0.05). We did not find significant evidence for linkage for baseline gait speed; however, we identified a potentially novel locus for change in gait speed on chromosome 16p (LOD 4.2). A subset of 21 families contributed to this linkage peak (HLOD = 6.83). Sequence analysis of the chromosome 16 region may yield new insight on the biology of age-related mobility decline.

Linkage Analysis of Genomic Regions Contributing to the Expression of Type 1 Diabetes Microvascular Complications and Interaction with HLA

We conducted linkage analysis to follow up earlier work on microvascular complications of type 1 diabetes (T1D). We analyzed 415 families (2,008 individuals) previously genotyped for 402 SNP markers spanning chromosome 6. We did linkage analysis for the phenotypes of retinopathy and nephropathy. For retinopathy, two linkage peaks were mapped: one located at the HLA region and another novel locus telomeric to HLA. For nephropathy, a linkage peak centromeric to HLA was mapped, but the linkage peak telomeric to HLA seen in retinopathy was absent. Because of the strong association of T1D with DRB1*03:01 and DRB1*04:01, we stratified our analyses based on families whose probands were positive for DRB1*03:01 or DRB1*04:01. When analyzing the DRB1*03:01-positive retinopathy families, in addition to the novel telomeric locus, one centromeric to HLA was identified at the same location as the nephropathy peak. When we stratified on DRB1*04:01-positive families, the HLA telomeric peak strengthened but the centromeric peak disappeared. Our findings showed that HLA and non-HLA loci on chromosome 6 are involved in T1D complications’ expression. While the HLA region is a major contributor to the expression of T1D, our results suggest an interaction between specific HLA alleles and other loci that influence complications’ expression.

Abstract 151: A Polymorphic T-Rich Element in ATP1B1 Is Associated with Blood Pressure and Regulates Alternative Polyadenylation

Genome-wide linkage and association studies of hypertension (HTN) aim to uncover loci that are involved in blood pressure (BP) regulation and the pathophysiology of HTN. However, even when such loci are successfully identified, the mechanism by which the implicated genes increase HTN susceptibility is not well understood. ATP1B1, which encodes the beta subunit of Na+, K+ ATPase, a co-transporter involved in multiple BP-regulating physiological processes, is located within a well-established BP linkage peak. Although a single nucleotide polymorphism (rs12079745) in the 3’UTR of ATP1B1 has previously been shown to be associated with BP levels, the molecular mechanism underlying this association is unknown. We identified a multi-allelic T-rich element (TRE) in the 3’UTR of ATP1B1 that varies in length and sequence composition (T22-27 and T12GT3GT6). The 3’UTR of ATP1B1 contains 2 functional polyadenylation signals and the TRE is downstream of the proximal site (A2). Because U-rich elements (UREs) in 3’UTRs are known to play a role in the cleavage and polyadenylation of mRNA, and ATP1B1 transcripts with shorter 3’UTRs are translationally more efficient, we hypothesized that alleles of this TRE might influence ATP1B1 expression by regulating alternative polyadenylation. Consistent with our hypothesis, the A2-polyadenylated mRNA isoform was more abundant in human kidneys with at least one copy of T12GT3GT6 than in those homozygous for the T22-27 alleles. Functionally, in vitro, we demonstrated that the T12GT3GT6 allele has greater luciferase activity than the T22 allele and that the T12GT3GT6 allele shows increased polyadenylation at the A2 site than the T22 allele. In addition, the TRE element is associated with systolic BP in European Americans of the GenNet network of the NHLBI Family Blood Pressure Program, with the T12GT3GT6 allele being associated with higher BP (effect size = 2.4 mmHg SBP, P = 0.003). Sharing strong linkage disequilibrium with rs12079745, this TRE is likely the functional site underlying the original association. In summary, we have identified a novel multi-allelic TRE in the 3’UTR of ATP1B1. Alleles at this site are associated with HTN and may mediate their effect on BP by regulating polyadenylation of the ATP1B1 mRNA.