Reduced neutrophil count in people of African descent is due to a regulatory variant in the Duffy antigen receptor for chemokines gene.

Persistently low white blood cell count (WBC) and neutrophil count is a well-described phenomenon in persons of African ancestry, whose etiology remains unknown. We recently used admixture mapping to identify an approximately 1-megabase region on chromosome 1, where ancestry status (African or European) almost entirely accounted for the difference in WBC between African Americans and European Americans. To identify the specific genetic change responsible for this association, we analyzed genotype and phenotype data from 6,005 African Americans from the Jackson Heart Study (JHS), the Health, Aging and Body Composition (Health ABC) Study, and the Atherosclerosis Risk in Communities (ARIC) Study. We demonstrate that the causal variant must be at least 91% different in frequency between West Africans and European Americans. An excellent candidate is the Duffy Null polymorphism (SNP rs2814778 at chromosome 1q23.2), which is the only polymorphism in the region known to be so differentiated in frequency and is already known to protect against Plasmodium vivax malaria. We confirm that rs2814778 is predictive of WBC and neutrophil count in African Americans above beyond the previously described admixture association (P = 3.8 x 10(-5)), establishing a novel phenotype for this genetic variant.

The interaction of P160 BCR with BCR-ABL gene products unique to Philadelphia chromosome leukemias

The BCR gene is involved in the pathogenesis of Philadelphia chromosome-positive (Ph$\sp1$) leukemias. Typically, the 5$\sp\prime$ portion of BCR on chromosome 22 becomes fused to a 5$\sp\prime$ truncated ABL gene from chromosome 9 resulting in a chimeric BCR-ABL gene. To investigate the role of the BCR gene product, a number of BCR peptide sequences were used to generate anti-BCR antibodies for detection of BCR and BCR-ABL proteins. Since both BCR and ABL proteins have kinase activity, the anti-BCR antibodies were tested for their ability to immunoprecipitate BCR and BCR-ABL proteins from cellular lysates by use of an immunokinase assay. Antisera directed towards the C-terminal portions of P160 BCR, sequences not present in BCR-ABL proteins, were capable of co-immunoprecipitating P210 BCR-ABL from the Ph$\sp1$- positive cell line K562. Re-immunoprecipitation studies following complete denaturation showed that C-terminal BCR antisera specifically recognized P160 BCR but not P210 BCR-ABL. These and other results indicated the presence of a P160 BCR/P210 BCR-ABL protein complex in K562 cells. Experiments performed with Ph$\sp1$-positive ALL cells and uncultured Ph$\sp1$-positive patient white blood cells established the general presence of BCR/BCR-ABL protein complexes in BCR-ABL expressing cells. However, two cell lines derived from Ph$\sp1$-positive patients lacked P160 BCR/P210 BCR-ABL complexes. Lysates from one of these cell lines mixed with lysates from a cell line that expresses only P160 BCR failed to generate BCR/BCR-ABL protein complexes in vitro indicating that P160 BCR and P210 BCR-ABL do not simply oligomerize.^ Two-dimensional tryptic maps were performed on both BCR and BCR-ABL proteins labeled in vitro with $\sp{32}$P. These maps indicate that the autophosphorylation sites in BCR-ABL proteins are primarily located within BCR exon 1 sequences in both P210 and P185 BCR-ABL, and that P160 BCR is phosphorylated in trans in similar sites by the activated ABL kinase of both BCR-ABL proteins. These results provide strong evidence that P160 BCR serves as a target for the BCR-ABL oncoprotein.^ K562 cells, induced to terminally differentiate with the tumor promoter TPA, show a loss of P210 BCR-ABL kinase activity 12-18 hours after addition of TPA. This loss coincides with the loss of activity in P160 BCR/P210 BCR-ABL complexes but not with the loss of the P210 BCR-ABL, suggesting the existence of an inactive form of P210 BCR-ABL. However, a degraded BCR-ABL protein served as the kinase active form preferentially sequestered within the remaining BCR/BCR-ABL protein complex.^ The results described in this thesis form the basis for a model for BCR-ABL induced leukemias which is presented and discussed. ^

Adiposity and the perilipin gene: The role of single locus and multilocus variation, obesity-related quantitative traits, and disease-related phenotypes in the Atherosclerosis Risk in Communities (ARIC) study

Obesity is a complex multifactorial disease and is a public health priority. Perilipin coats the surface of lipid droplets in adipocytes and is believed to stabilize these lipid bodies by protecting triglyceride from early lipolysis. This research project evaluated the association between genetic variation within the human perilipin (PLIN) gene and obesity-related quantitative traits and disease-related phenotypes in Non-Hispanic White (NHW) and African American (AA) participants from the Atherosclerosis Risk in Communities (ARIC) Study. ^ Multivariate linear regression, multivariate logistic regression, and Cox proportional hazards models evaluated the association between single gene variants (rs2304794, rs894160, rs8179071, and rs2304795) and multilocus variation (rs894160 and rs2304795) within the PLIN gene and both obesity-related quantitative traits (body weight, body mass index [BMI], waist girth, waist-to-hip ratio [WHR], estimated percent body fat, and plasma total triglycerides) and disease-related phenotypes (prevalent obesity, metabolic syndrome [MetS], prevalent coronary heart disease [CHD], and incident CHD). Single variant analyses were stratified by race and gender within race while multilocus analyses were stratified by race. ^ Single variant analyses revealed that rs2304794 and rs894160 were significantly related to plasma triglyceride levels in all NHWs and NHW women. Among AA women, variant rs8179071 was associated with triglyceride levels and rs2304794 was associated with risk-raising waist circumference (>0.8 in women). The multilocus effects of variants rs894160 and rs2304795 were significantly associated with body weight, waist girth, WHR, estimated percent body fat, class II obesity (BMI ≥ 35 kg/m2), class III obesity (BMI ≥ 35 kg/m2), and risk-raising WHR (>0.9 in men and >0.8 in women) in AAs. Variant rs2304795 was significantly related to prevalent MetS among AA males and prevalent CHD in NHW women; multilocus effects of the PLIN gene were associated with prevalent CHD among NHWs. Rs2304794 was associated with incident CHD in the absence of the MetS among AAs. These findings support the hypothesis that variation within the PLIN gene influences obesity-related traits and disease-related phenotypes. ^ Understanding these effects of the PLIN genotype on the development of obesity can potentially lead to tailored health promotion interventions that are more effective. ^