Healthy African American Subjects Research Articles

Abstract B48: Similar prevalence of t(14,18) in African American and Caucasian subjects

Abstract Background: It has been shown that t(14;18), a translocation involving IgH and BCL-2 genes that is present in over 80% of all cases of follicular lymphomas, is detectable in the peripheral blood of up to 52% of normal Caucasian patients from Germany and up to 16% of normal individuals from Japan (Yasukawa et al, Blood 2001). The fact that follicular lymphoma is one of the two most common lymphomas in the USA and Germany and much less common in Japan, demonstrates that this molecular alteration is perhaps an early event in the development of this malignancy which is not sufficient for its causation. There have not been any studies evaluating the prevalence of this translocation in healthy African American (AA) subjects. We speculated that the prevalence of this translocation will be lower in healthy AA subjects given the findings of lower prevalence of IgH translocations in AA patients with multiple myeloma compared with Caucasian patients, which may explain the better outcome of myeloma in AA subjects (Baker et al, Blood 2013). This effort to evaluate the prevalence of t (14; 18) in AA subjects, was part of a pilot study in which we brought an educational program on the importance of cancer research together with concomitant access to a translational research project to AA churches utilizing a mobile research unit in an attempt to overcome some of the known barriers to AA subject participation in clinical research (Colon-Otero et al, Cancer2008; Colon-Otero et al, J Cancer Educ 2012). Methods: IRB approval of the project was obtained and peripheral blood samples collected from consented subjects during educational sessions in Northeast Florida AA Churches. Caucasian subjects were identified from the Mayo Clinic Bio-bank. DNA was isolated from the buffy coat fractions and a PCR quality control assay targeting a 293bp fragment of an HLA class II gene was used to determine acceptable DNA quality and quantity. Next, a two-step semi-nested PCR was performed on the t (14;18) major and minor breakpoint cluster regions using ~500ng of DNA for each assay. A consensus JH primer was used in combination with primers complementary to BCL-2 sequences for both, the major and minor breakpoint cluster regions. PCR products were run on a 1% agarose gel. In order to confirm the positive results, positive PCR products were analyzed by direct sequence by Sanger method and subsequently assembled to the human genome using BLAST tool. Results: A total of 110 blood samples from AA subjects were analyzed for the presence of t (14;18). A total of 13 of the samples were positive for the major breakpoint site (12%) and 4 were positive for the minor breakpoint site (4%), for a total of 17 positive samples (15%). In 167 Caucasian patients samples, a total of 22 (13%) were positive for the major breakpoint site and 5 (3%) were positive for the minor breakpoint site for a total of 27 positive samples (16%). All cases were confirmed by Sanger sequencing. Conclusions: The prevalence of t(14;18) is not significantly different among African American and Caucasian subjects from the USA based on our findings. This represents the first report of the prevalence of t(14;18) in an African American population. The prevalence found in our Caucasian subjects is significantly lower than what had been described in previous population series. A plausible explanation is the high heterogeneity of approaches used across studies, significantly affecting the assay sensitivity. Additional studies with larger series may reveal minor differences in the prevalence of t(14;18) among these populations. Citation Format: Scott Van Wier, Gerardo Colon-Otero, Gregory Ahmann, Esteban Braggio, Monica Albertie, Sikander Ailawadhi, Rafael Fonseca. Similar prevalence of t(14,18) in African American and Caucasian subjects. [abstract]. In: Proceedings of the Eighth AACR Conference on The Science of Health Disparities in Racial/Ethnic Minorities and the Medically Underserved; Nov 13-16, 2015; Atlanta, GA. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2016;25(3 Suppl):Abstract nr B48.

Abstract 16819: Sequencing of Genetic Loci Associated With Leukocyte Telomere Length Reveals New Intronic Variants in African Americans

Background: Shorter telomere length is associated with an increased risk of coronary artery disease (CAD). A prior genomewide association study (GWAS) on 37,684 European ancestry individuals identified seven loci determining leukocyte telomere length (LTL). A genetic risk score across all 7 loci showed an association with CAD. In this study we sequenced these loci to determine whether the same risk variants could be replicated in African admixed individuals. Methods: We used whole genome sequence data (WGS) in 127 healthy African American subjects from GeneSTAR, a family study of early-onset CAD. LTL was calculated from WGS raw bam data (>30x coverage on the Illumina HiSeq platform) for 7 contiguous repeats of the telomere motif (TTAGGG or CCCTAA, Ding et al., 2014). Tests for association for LTL adjusting for age and sex were performed for a total of 55,821 called variants from ~1Mb subset regions of WGS genotype data centered on each of the 7 European peak GWAS SNPs. Results: We identified a total of 17 variants with p<5x10 -4 mapping to 6 of the 7 regions examined; none of the prior European GWAS peak SNPs were significant. The peak SNP per region in the African Americans included intronic variants rs77138331 in ACYP2 (p=0.0005, MAF = 7%), rs149577640 in NAF1 (p=0.002, MAF=1%), rs35387865 in TERT (p=0.003, MAF = 1%) and rs186486116 in OBFC1 (p=0.004, MAF=1%). Additionally, novel intronic variants not previously observed in dbSNP located at chr19: 22190184 (p=0.005, MAF=1%) and chr2:62445438 (0.005, MAF=2%), mapping to ZNF208 and RTEL1 , were also identified as determinants of LTL. Discussion: This is the first study of telomere length in African Americans using a sequencing approach. We are unable to confirm the European-based GWAS variants but identify several associations mapping to genes of importance in telomere biology. Our results provide evidence that the set of SNPs to be included in calculation of a telomeric genetic CAD risk score may be different in populations of European and African ancestry.

Mitochondrial Uncoupling Protein 2 Is Present in Human Platelets and Regulates Platelet Activation

It has long been recognized that platelets contain functional mitochondria and accumulating data suggest that several aspects of mitochondrial function, including reactive oxygen species production, modulate platelet thrombotic function. We have recently shown that platelet mitochondria isolated from patients with Sickle Cell Disease generate significantly greater concentrations of reactive oxygen species than healthy African American subjects and that this mitochondrial oxidant generation contributes to higher levels of basal platelet activation in these patients (Blood. 2014 May 1;123(18):2864-72). Based on these data, we have now investigated the factors that regulate platelet mitochondrial superoxide generation in healthy and Sickle Cell Disease platelets. Here we demonstrate that human platelets express mitochondrial uncoupling protein-2 (UCP2), a protein that is known to decrease the efficiency of oxidative phosphorylation and oxidant generation in other cell types but has previously not been identified in platelets. In this study we show that UCP2 protein is expressed in healthy human platelets and is fully functional as it facilitates proton leak across the inner mitochondrial membrane, leading to decreased mitochondrial membrane potential. Further, we demonstrate that the expression of this protein attenuates platelet mitochondrial superoxide generation, as treatment of platelets with Genipin (2-10µM), a pharmacological inhibitor of UCPs, concentration-dependently increases mitochondrial membrane potential and reactive oxygen species production. Further, an approximately 70% inhibition of UCP activity results in platelet activation demonstrated by increased membrane p-selectin expression (65±7% versus 6±3% in untreated controls) and augmented glycoprotein IIb/IIIa activation (57±9% versus 9±4% in untreated controls). The use of the mitochondrial-targeted antioxidant mitoTEMPO (10µM) decreases genipin-induced superoxide generation and significantly attenuates platelet activation. Notably, preliminary data presented here also suggest that UCP expression is decreased in platelets isolated from Sickle Cell Disease patients (3-fold) compared to healthy African American subjects. Additionally, ongoing studies are investigating platelet function in mice deficient in UCP2. Taken together, these data demonstrate a novel mechanism of regulation of platelet thrombotic function whose physiological relevance is apparent in the context of Sickle Cell Disease. More broadly this study advances the understanding of the role of the mitochondrion in platelet biology and thrombotic disease. DisclosuresNo relevant conflicts of interest to declare.

Fourteen Percent of Healthy African Americans Participating In the Zimmerman Program for the Molecular and Clinical Biology of VWD (ZPMCB VWD) Are Heterozygous for the VWF Gene Mutation H817Q Associated with Type 2N Von Willebrand Disease

AbstractAbstract 239Von Willebrand disease (VWD) is a common hereditary bleeding disorder caused by reduced concentration or abnormal structure/function of von Willebrand Factor (VWF). Most published studies of normal VWF have been carried out in European or North American subjects without regard to racial differences. In the process of studying healthy controls in the Zimmerman Program for the Molecular and Clinical Biology of VWD (ZPMCB-VWD), we identified a common polymorphism (D1472H) in the VWF A1-domain in African Americans that affects the measurement of VWF function by ristocetin cofactor (VWF:RCo) but does not appear associated with increased bleeding risk. We therefore explored whether other polymorphisms or mutations were identified more frequently in African Americans. VWF sequencing was performed on 191 healthy controls including 66 that were self-identified as African American. European Bleeding Score was obtained and normal in all healthy subjects. Among the African Americans, 9 individuals were heterozygous for the reported type 2N H817Q mutation and one was homozygous. Factor VIII binding to VWF (VWF:F8B) was determined with a standard FVIII binding assay using the subject's plasma VWF and recombinant FVIII. The VWF:F8B was significantly reduced in H817Q heterozygotes when compared to 10 healthy study subjects without the H817Q mutation (65 ± 11 versus 108 ± 11, p=0.003). The VWF:F8B was further reduced to 37 using the plasma VWF from the homozygous H817Q subject. However, the observed VWF:F8B in these individuals with H817Q are still considerably higher that that observed in patients enrolled in ZPMCB-VWD that are either homozygous or compound heterozygous with the common R854Q type 2N VWD (VWF:F8B < 13). Of the 116 self-identified Caucasian healthy subjects, none had the H817Q mutation, but 3 were heterozygous for the R854Q mutation; their mean plasma VWF:F8B was reduced to 51. While the homozygous R854Q patients had reduced plasma FVIII levels (mean FVIII=24 IU/dL), none of the sequenced healthy control subjects had plasma FVIII levels below 53 IU/dL, Some have advocated FVIII/VWF:Ag ratios as a screen for type 2N VWD. The subject with homozygous H817Q had only a mildly reduced FVIII/VWF:Ag ratio (0.59), while the heterozygous H817Q were not reduced (mean=0.90), thereby demonstrating that the VWF:F8B assay has greater sensitivity for type 2N VWF binding defects than the FVIII/VWF:Ag ratio. Since the previously reported A1-domain D1472H polymorphism was common in African Americans, we explored the prevalence of this polymorphism in the healthy subjects with the H817Q mutation. All H817Q heterozygous subjects were either homozygous (4) or heterozygous (5) for the D1472H polymorphism. The one individual who was H817Q homozygous was also D1472H homozygous, suggesting that there may be an extended haplotype present in African Americans. In summary, an H817Q type 2N mutation is commonly found in healthy African American subjects with an allele frequency of 0.083, predicting that approximately 7 in 1,000 African Americans would be homozygous for the H817Q type 2N mutation. Our data, and the rarity of diagnosis of type 2N VWD in African Americans suggests that while mutation H817Q may interfere with the interaction of FVIII with VWF, this mutation appears to confer little or no clinical symptoms. Disclosures:No relevant conflicts of interest to declare.

Filaggrin mutations that confer risk of atopic dermatitis confer greater risk for eczema herpeticum

Loss-of-function null mutations R501X and 2282del4 in the skin barrier gene, filaggrin (FLG), represent the most replicated genetic risk factors for atopic dermatitis (AD). Associations have not been reported in African ancestry populations. Atopic dermatitis eczema herpeticum (ADEH) is a rare but serious complication of AD resulting from disseminated cutaneous herpes simplex virus infections. We aimed to determine whether FLG polymorphisms contribute to ADEH susceptibility. Two common loss-of-function mutations plus 9 FLG single nucleotide polymorphisms were genotyped in 278 European American patients with AD, of whom 112 had ADEH, and 157 nonatopic controls. Replication was performed on 339 African American subjects. Significant associations were observed for both the R501X and 2282del4 mutations and AD among European American subjects (P = 1.46 x 10(-5), 3.87 x 10(-5), respectively), but the frequency of the R501X mutation was 3 times higher (25% vs 9%) for ADEH than for AD without eczema herpeticum (EH) (odds ratio [OR], 3.4; 1.7-6.8; P = .0002). Associations with ADEH were stronger with the combined null mutations (OR, 10.1; 4.7-22.1; P = 1.99 x 10(-11)). Associations with the R501X mutation were replicated in the African American population; the null mutation was absent among healthy African American subjects, but present among patients with AD (3.2%; P = .035) and common among patients with ADEH (9.4%; P = .0049). However, the 2282del4 mutation was absent among African American patients with ADEH and rare (<1%) among healthy individuals. The R501X mutation in the gene encoding filaggrin, one of the strongest genetic predictors of AD, confers an even greater risk for ADEH in both European and African ancestry populations, suggesting a role for defective skin barrier in this devastating condition.

Normative values for exhaled breath condensate pH and its relationship to exhaled nitric oxide in healthy African Americans

Exhaled breath condensate (EBC) pH and exhaled nitric oxide (FeNO) have been proposed as markers of asthma severity. EBC pH values below 6.5 have been associated with asthma exacerbations. Protonation of airway nitrite occurs at low pH and may contribute to FeNO. To establish normative EBC pH values and to determine the contribution of EBC pH to FeNO in healthy African Americans. Two hundred seventy healthy African American subjects without asthma between 18 and 40 years old were evaluated. Subjects had simultaneous measurement of EBC pH, EBC nitrite, nitrate, and FeNO. The median EBC pH was 8.14 (interquartile range, 7.83-8.28). Of subjects, 11.9% had an EBC pH < or = 6.5. In subjects with EBC pH values below 6.5, there was an inverse correlation between EBC pH and FeNO (r(2) = 0.158; P = .0245; n = 32). In the entire cohort, there was a direct correlation between EBC pH and EBC nitrite (r(2) = 0.163; P < .0001), but there was no correlation between EBC nitrite and FeNO. In multivariate analyses, EBC pH and nitrite did not contribute significantly to FeNO variation while controlling for other confounders of FeNO. There was an increased prevalence (11.9%) of low EBC pH (less than 6.5) in healthy African American subjects compared with white subjects (<5%). EBC pH and nitrite were directly correlated, but there was no correlation between EBC nitrite and FeNO. FeNO correlated with EBC pH at pH values less than 6.5 in univariate but not multivariate analyses. This suggests that EBC pH and nitrite are not significant determinants of FeNO in healthy subjects.

Identification of functionally variant MDR1 alleles among European Americans and African Americans.

MDR1 (P-glycoprotein) is an important factor in the disposition of many drugs, and the involved processes often exhibit considerable interindividual variability that may be genetically determined. Single-strand conformational polymorphism analysis and direct sequencing of exonic MDR1 deoxyribonucleic acid from 37 healthy European American and 23 healthy African American subjects identified 10 single nucleotide polymorphisms (SNPs), including 6 nonsynonymous variants, occurring in various allelic combinations. Population frequencies of the 15 identified alleles varied according to racial background. Two synonymous SNPs (C1236T in exon 12 and C3435T in exon 26) and a nonsynonymous SNP (G2677T, Ala893Ser) in exon 21 were found to be linked (MDR1*2 ) and occurred in 62% of European Americans and 13% of African Americans. In vitro expression of MDR1 encoding Ala893 (MDR1*1 ) or a site-directed Ser893 mutation (MDR1*2 ) indicated enhanced efflux of digoxin by cells expressing the MDR1-Ser893 variant. In vivo functional relevance of this SNP was assessed with the known P-glycoprotein drug substrate fexofenadine as a probe of the transporter's activity. In humans, MDR1*1 and MDR1*2 variants were associated with differences in fexofenadine levels, consistent with the in vitro data, with the area under the plasma level-time curve being almost 40% greater in the *1/*1 genotype compared with the *2/*2 and the *1/*2 heterozygotes having an intermediate value, suggesting enhanced in vivo P-glycoprotein activity among subjects with the MDR1*2 allele. Thus allelic variation in MDR1 is more common than previously recognized and involves multiple SNPs whose allelic frequencies vary between populations, and some of these SNPs are associated with altered P-glycoprotein function.

Dextromethorphan O-demethylation polymorphism in an African-American population.

One hundred eighty-one (97 F, 84 M) unrelated healthy African-American subjects (aged 18-41 years) were phenotyped based on their dextromethorphan (DMP) O-demethylation ability. Each subject was given 15 mg DMP orally and collected 8-h urine. The concentrations of DMP and its metabolite dextrophan (DOP) were determined by HPLC with ultraviolet detection. Metabolic ratio (MR) was expressed as the ratio of DMP to DOP molar amount in urine. The frequency distribution histogram of the MR was bimodal, and probit analysis of this frequency gave an antimode value of 0.34. Seven subjects [3.9%, 95% confidence interval (CI) 1.1%-6.7%] were classified as poor metabolizers (PMs). This deficient frequency is in complete agreement with the reported ones in two smaller investigations in the African-American populations.