Reference
Complete the bibliographic reference for the article according to AJE format.

Mikkelsson J, Perola M, Penttila A, Karhunen, PJ.  Platelet Glycoprotein Ib a HPA-2 Met/VNTR B haplotype as a genetic predictor of myocardial infarction and sudden cardiac death.  Circulation 2001;104:876-80.

Category of HuGE information
Specify the types of information (from the list below) available in the article:

1. Prevalence of gene variant
2. Gene-disease association
3. Gene-environment interaction
4. Gene-gene interaction
5. Genetic test evaluation/monitoring

1. Gene prevalence
2. Gene-disease association
3. Gene-environment association

Study hypotheses or purpose
The authors study hypotheses or main purpose for conducting the study.

Hypothesis: Current studies have shown conflicting evidence about the relation of HPA-2/VNTR polymorphism and coronary heart disease (CHD) measures.  The authors hypothesize that the HPA-2 Met/VNTR B haplotype will be associated with an increased risk of CHD, including sudden cardiac death, myocardial infarction, coronary atherosclerosis, coronary stenosis, and coronary thrombosis.

Gene(s)
Identification of the following:

1. Gene name
2. Chromosome location
3. Gene product/function
4. Alleles
5. OMIM #

1. Gene: GP Ib alpha
2. Chromosome location:  17pter-p12
3. Gene product/function: The alpha chain of platelet glycoprotein Ib; the intact protein platelet glycoprotein Ib consists of a disulfide-linked alpha and beta chain and serves as the platelet receptor for the von Willebrand factor.  The alpha chain portion provides the binding site for the von Willebrand factor.  Platelet Glycoprotein Ib also serves as a thrombin receptor.
4. Allele
   • HPA-2 polymorphism (Thr to Met transition)
   • molecular weight polymorphism: alleles A, B, C, and D where there are a variable number of tandem repeats of 13 amino acids in the macroglycopeptide region of the protein.  The largest allele is A and the smallest D; each allele differs in size by 39 base pairs (i.e., A is larger than B by 39 base pairs, B larger than C by 39 base pairs, and C larger than D by 39 base pairs [1])
5. OMIM #: 231200

Environmental factor(s)
Identification of the major environmental factors studied (infectious, chemical, physical, nutritional, and behavioral)

Health outcome(s)
Identification of the major health outcome(s) studied

1. Sudden cardiac death (SCD)
2. Myocardial infarction (MI)
3. Coronary artery stenosis (CAS)
4. Coronary artery atherosclerosis (CAA)
5. Coronary thrombosis (CT)

1. Case-control
2. Cohort 
3. Cross-sectional
4. Descriptive or case series
5. Clinical trial
6. Population screening

Case definition
For study designs 2, 3, and 6, the following are defined, where available:

1. Case selection criteria
2. Exclusion criteria
3. Gender
4. Race/ethnicity
5. Age
6. Time period
7. Geographic location
8. Number of participants

The subjects were part of the Helsinki Sudden-Death Study, in which men who were subjected to a medicolegal autopsy at the Department of Forensic Medicine, University of Helsinki from1981 to 1982 (n=400) and from 1991 to 1992 (n=300) were included in the study.  Indications for autopsy included out-of-hospital death of a previously healthy man, suspected intoxication, suicide, or death in connection with medical treatment.  Causes of death included cardiovascular diseases (n=288), other diseases (n=140), and suicides and accidents (n=272). The mean age of those who died from sudden cardiac death was 56.5 (+/- 8.6) years; the mean age of those who died a violent death was 49.2 (+/- 9.4) years; the mean age of those who died from other diseases was 53.5 (+/- 8.9) years.

1. Disease case definition:  SCD was identified using autopsy data.
   MI was identified using macroscopic and histological examination of the myocardium; acute myocardial infarction (AMI) was determined by the presence or absence of neutrophil granulocytes and old MI by the presence/absence of fibrous scar tissue.  CAS was measured in the left anterior descending, left circumflex, and right coronary arteries using coronary angiography with simultaneous rubber casting of the arteries and was reported as the percent stenosis. Percent stenosis was calculated by dividing the diameter of greatest stenosis by the diameter of the nearest undamaged part of cast model of the artery.  CAA was determined using stains specific for fat and reported using the proportional area of each atherosclerotic change in the most-affected coronary artery.
2. Exclusion criteria:  Not mentioned
3. Gender:  Males only
4. Race/ethnicity:  Caucasians (Finnish)
5. Age:  Mean age of the entire group (cases and controls) was 53 years (range 33 to 70 years).
6. Time period:  Two autopsy series were conducted; the first from 1981 to 1982 and the second from 1991 to 1992.
7. Geographic location:  Helsinki , Finland and its surrounding area
8. Number of participants:  All MIs- 172

Control definition
For study design 1, the following are defined, if available:

1. Control selection criteria
2. Matching variables
3. Exclusion criteria 
4. Gender
5. Race/ethnicity
6. Age
7. Time period
8. Geographic location
9. Number of participants

1. Control selection criteria: Controls were defined as controls if their cause of death was noncardiac and if they had little or no significant coronary disease or MI at autopsy.
2. Matching variables: none
3. Exclusion criteria: none mentioned
4. Gender: Males 
5. Race/ethnicity: Caucasian 
6. Age: Mean age of the entire group (cases and controls) was 53 years (range 33 to 70 years).  
7. Time period: Two autopsy series were conducted; the first between 1981 and 1982 and the second between 1991 and 1992.
8. Geographic location: Helsinki , Finland and its surrounding area
9. Number of participants: 367 men

1. Environmental factor
2. Exposure assessment
3. Exposure definition
4. Number of participants with exposure data (%
   of total eligible)

1. Environmental factor: Cigarette smoking, alcohol consumption
2. Exposure assessment: A spouse, relative, or friend was interviewed.
3. Exposure definition: Men were defined either as smokers (79.6%) or nonsmokers, with ex-smokers being placed in the category of smoker. History of alcohol consumption was defined as average drinks per day.
4. Number of participants with exposure data: 500 (71.4%) men

1. Gene
2. DNA source
3. Methodology
4. Number of participants genotyped (% of total eligible) 

1. Gene: GP Ib alpha
2. DNA source: In the 1981-to-1982 series, DNA was extracted from paraffin-embedded samples of cardiac muscle, and in the 1991-to-1992 series, DNA was isolated from frozen       (-70ºC) cardiac muscle samples.
3. Methodology: The HPA-2 polymorphism was performed with restriction polymorphism analysis with slight modifications from Kekomaki et al., and the VNTR polymorphism genotyping was done directly using the procedure of Kekomaki et al. (2).
4. Participants genotyped: Successful genotyping data for both polymorphisms was obtained for 626 participants (89.4%).

1. Prevalence of gene variant
2. Gene-disease association
3. Gene-environment interaction
4. Gene-gene interaction
5. Genetic test evaluation/monitoring

1. Prevalence of gene variant in 626 men:

Linkage disequilibrium between the VNTR and HPA-2 polymorphisms of GP Ib

HPA-2 Genotype Prevalence

Allele frequencies for Thr and Met were 0.88 and 0.12, respectively. VNTR Genotype Prevalence

No men had A/A, A/B, or A/D genotypes.  The allele frequencies for the A, B, C and D alleles were 0.0008, 0.13, 0.78, and 0.087, respectively.

Because of the anticipated strong linkage disequilibrium between HPA-2 and the VNTR (a haplotype effect confined to HPA - Met/ VNTR B versus Met-negative/VNTR B-negative), the investigators were unable to distinguish independent effects of the two polymorphisms; thus, all analyses were conducted using only the HPA-2 genotyping data.*

2. Gene-disease association

* Analysis adjusted for risk factor data: smoking, hypertension, alcohol consumption, and diabetes.

Similar associations to those shown above were observed in the separate analyses of both autopsy series.

There was an interaction between age groups (< 55 years of age  versus > 55 years of age) and the HPA-2 polymorphism on SCD, coronary thrombosis, and acute MI.

The frequency of the HPA-2 Met allele in men > 55 years of age was similar among the men with SCD, coronary thrombosis, AMI, or any MI when compared to controls.  The frequency of this allele was significantly higher in men < 55 years of age with SCD, coronary thrombosis, and AMI compared to controls in the same age group. In addition, men < 55 with the HPA-2 allele had more severe stenosis and a larger vessel-wall area covered by raised lesions compared to noncarrier of this allele (data not shown).

3.  Gene-environment interaction

The authors conclude that the HPA-2 Met/VNTR B of the platelet von Willebrand factor and the thrombin receptor GP Ib-V-IX is associated with coronary thrombosis, AMI and SCD among early middle-aged men (< 55 years of age).

Comments
Provide additional insight, including methodologic issues and/or concerns about the study

Of note is that the population of individuals in the Helsinki Sudden-Death Study have a high proportion of smokers (prevalence of smoking 79.6% in entire group and 79.3% in those younger than age of 55 years) and have high alcohol consumption (mean number of drinks per day ranged from five for those who died of SCD to 10 for those who had violent deaths).  Further, the prevalence of hypertension and diabetes are both relatively high, especially amongst those younger than 55 years of age; the diabetes prevalence amongst those younger than 55 years of age was 20.8% and the hypertension prevalence was 16.5%. Given the distribution of these risk factors, the generalizability of the study results to other populations may be somewhat limited.  Furthermore, since the study only included deceased men from Finland , the relation between the polymorphism in living, diverse populations needs to be studied.

One of the biggest challenges to studying the GP Ib alpha HPA/VNTR haplotypes and their association with disease risk is the linkage disequilibrium that exists between HPA and the VNTR.   Discovery of an association does not reveal which one is the polymorphism responsible for the increased risk; nor does the finding of an increased risk necessarily implicate only the HPA or the VNTR as the responsible polymorphism.

Other rare variants of the GP Ib alpha exist; these variants play a role in Bernard-Soulier syndrome and Von Willebrand disease.  These variants can be found in OMIM 231200.

A weakness of the presentation of this study is knowing exactly how many subjects had data on both the polymorphisms and the covariates.

Finally, the deceased men in the Helsinki Sudden-Death Study have been investigated for associations between other genetic polymorphisms and various disease endpoints. (3,4,5,6)  Thus, the potential may exist to eventually investigate gene-gene interactions in this study group.