No Association of PLIN Polymorphisms With Hemorrhagic and Ischemic Stroke
Background and Purpose— Perilipin is encoded by the gene PLIN and mediates lipid metabolism. Its upregulation has been linked to the formation of foam cells, rupture of atherosclerotic plaques, and perhaps acute coronary syndrome. We hypothesized that genetic variations in PLIN might contribute to the susceptibility to stroke. The hypothesis was tested in 2 case–control studies.
Methods— Six PLIN tag single nucleotide polymorphisms (rs7176403, rs8179078, rs6496589, rs8179043, rs894160, rs1052700) were genotyped in 1571 patients with stroke (690 cerebral thrombosis, 429 lacunar infarction, 452 intracerebral hemorrhage) and 1638 control subjects. A SHEsis software platform was used to analyze pairwise linkage disequilibrium and haplotype association in the case–control study. The study was replicated in another independent case–control study including 120 patients with stroke and 240 control subjects.
Results— No association of the PLIN variants with stroke (P>0.05) or with stroke subtypes (P>0.05) was found in the first study. The findings were confirmed in the second population (P>0.05).
Conclusions— The data represent an important negative finding that the common variants of PLIN do not have a major effect on susceptibility to stroke in a Chinese population.
Perilipin is encoded by gene PLIN and mediates lipid metabolism. Upregulation of perilipin has been linked to abnormal lipid metabolism, the development of atherosclerosis, and destabilizing atherosclerotic plaque1–6 such as the formation of foam cells, rupture of atherosclerotic plaques, and perhaps acute coronary syndrome. We hypothesized that genetic variations in PLIN might contribute to the susceptibility to stroke. The hypothesis was tested in 2 case–control studies.
Patients With Stroke and Control Subjects
Initially, 2000 patients with stroke and 2000 control subjects were recruited in the first study as described previously.7–9 A total of 791 subjects were excluded at different experimental stages: lack of definite diagnosis (24), absence of plasma (76 cases and 93 control subjects), or failure to detect PLIN genotypes (349 cases, 249 control subjects). No significant difference was found in the characteristics between the included and excluded subjects. The characteristics of cases and control subjects in the first study are shown in Table 1. In the second population, the patients (120) and control subjects (240) were recruited following the criteria of the first study.
No Obvious Population Stratification in the Case–Control Study
In minimizing population stratification confounding effects, each of the 2 study populations is a single Han nationality. The cases and control subjects were matched by specific geographic regions. We additionally genotyped 11 unlinked microsatellite markers in the first population and found no significant allele-frequency differences between control subjects and patients with stroke within each clinic center and between these centers (χ2=62.1, df=60, P=0.40), indicating no obvious genetic stratification in the first study population.
No Association of PLIN Polymorphism With Stroke
To better cover the common variations across the PLIN, the selection of the single nucleotide polymorphisms (SNPs) was based on the HapMap CHB sample using the pairwise option of the Haploview version of the Tagger program. A minimum r2 of 0.8 was chosen as a threshold for all analyses. Six tagSNPs with a minor allele frequency more than 5% were genotyped within a 35.99-kilobase region spanning the PLIN and PEX11A on chromosome 15 (87999045… 88035030). SNP rs7176403 is located in PEX11A intron 2 and in strong linkage disequilibrium with the SNPs rs7169981, rs1972435, and rs1561725 in the PEX11A, 5′ adjacent region of the PLIN and rs4578621 in the first intron. These 5 SNPs are in complete association with one another (D′=1.0, r2=1.0). SNP rs8179078 is located in the PLIN promoter region; rs6496589 in PLIN exon 5; rs8179043 in PLIN intron 6; rs894160 in PLIN intron 6; rs1052700 in PLIN exon 9; and PEX11A is adjacent to PLIN. SNPs rs8179043, rs1052700, and rs6496589 capture rs2289487, rs12595195, and rs894161, respectively. The other 2 tag SNPs (rs8179078 and rs894160) do not capture the other SNPs. The selective neutrality of the polymorphisms under investigation was confirmed by using ARLEQUIN (Ewens-Watterson neutrality tests, supplemental Table I, available online at http://stroke.ahajournals.org).
To avoid false-positive association, all aspects of DNA source, preparation, and genotyping were controlled using the paradigms of blindness and randomization. The genotype frequencies for all 6 polymorphisms are in accordance with Hardy-Weinberg equilibrium (P>0.05) in both cases and control subjects. The lowest frequency threshold for haplotype analysis was 0.05. Assuming a dominant model, the study had more than 80% statistical power to detect an association (at P=0.05) with ORs of 1.3 to 2.5 for alleles at 12% to 33% frequency, indicating a low risk of a false-negative result.
No linkage disequilibrium was found between any pairwise among the 6 selected SNPs using a SHEsis software platform.10 Neither the genotype nor the allele frequencies of studied polymorphisms were significantly different between the patients and the control subjects and between subtypes of stroke and control subjects before and after adjustment for the conventional cardiovascular risk factors (including age, sex, history of hypertension, diabetes, blood pressure, body mass index, cigarette smoking, glucose, total cholesterol, high-density lipoprotein cholesterol, and triglycerides, lipoprotein[a], and alcohol use) (Table 2). Six major haplotypes with frequencies >5% were identified, accounting for more than 80% of all chromosomes in the 2 study populations. No significant difference was found in haplotype frequencies between cases and control subjects in the first study (Table 3).
The observation was confirmed in the second study (supplemental Table II).
Our results reject our hypothesis. Although perilipin has been linked to the formation of foam cells, rupture of atherosclerotic plaques, and perhaps acute coronary syndrome, the PLIN polymorphisms do not have a major effect on susceptibility to stroke at least in Chinese population. To our knowledge, the role of genetic variation in PLIN in susceptibility of stroke has not been investigated before.
We express our sincere thanks to Drs Lin Wang, Xue Wang, Dongmei Meng, Guolu Meng, Luhong Wan, Shihao Zhang, Weili Zhang, and Chaoshu Tang for their help.
Source of Funding
This research was supported by 973 Project from the Ministry of Science and Technology of China (2006CB503805 to R.H.).
- Received June 11, 2007.
- Revision received July 11, 2007.
- Accepted July 17, 2007.
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