Donate Help Contact The AHA Sign In Home
American Heart Association
Stroke
Search: search_blue_button Advanced Search
Table of Contents | Next Article »
Stroke. 2006;37:1955-1957
Published online before print July 6, 2006, doi: 10.1161/01.STR.0000234048.04053.39
This Article
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
37/8/1955    most recent
01.STR.0000234048.04053.39v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Worrall, B. B.
Right arrow Articles by Mychaleckyj, J. C.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Worrall, B. B.
Right arrow Articles by Mychaleckyj, J. C.
Right arrowPubmed/NCBI databases
Medline Plus Health Information
*Stroke
Related Collections
Right arrow Genetics of Stroke
Right arrow Risk Factors for Stroke

(Stroke. 2006;37:1955.)
© 2006 American Heart Association, Inc.

Editorials

PDE4D and Stroke

A Real Advance or a Case of the Emperor’s New Clothes?

Bradford B. Worrall, MD, MSc Josyf C. Mychaleckyj, MA, DPhil

From the University of Virginia Health System (B.B.W.), Departments of Neurology and Public Health Sciences, Charlottesville, Va; and the Center for Human Genomics (J.C.M.), Wake Forest University School of Medicine, Winston-Salem, NC.

Correspondence to Bradford B. Worrall, MD, MSc, University of Virginia Health System, Department of Neurology, Box 800394, Charlottesville, VA 22908. E-mail bbw9r{at}virginia.edu


Key Words: genetics • hypertension • phosphodiesterase • polymorphism, genetic • stroke

See related article, pages 2012–2017.

In Hans Christian Andersen’s beloved tale,1 it is the innocent child who finally reveals what others had been unable to admit. Deference to the King’s court and perceived wisdom discomforts other subjects in the kingdom from questioning the sovereign’s taste in garments. Since the original article identifying PDE4D as the putative stroke 1 (STRK1) locus,2 many groups from around the globe have attempted to validate the association. Stroke is a syndrome not a disease, with numerous interrelated phenotypes and subphenotypes. The challenges of sorting out the genetic contributions to complex diseases such as stroke are substantial, but the potential rewards in the forms of new treatments and improved understanding of pathophysiology are great. In the face of the great promise of the PDE4D tale, we need to assess the state of our knowledge clearly and honestly.

Before the report by deCODE Genetics, the PDE4 family of genes had not been tested as candidate genes for any disease or phenotype, although the biochemical role of PDE4D as a regulator of cAMP signal transduction was recognized. The PDE4D gene product (cAMP specific 3',5'-cyclic phosphodiesterase 4D) appears to be a secondary signal pathway regulator of phenotype, with indirect effects on cardiovascular or stroke biomarkers.3 Nonetheless, because PDE4 enzymes predominate cAMP metabolism in inflammatory cells, and PDE4D accounts for at least 80% of PDE activity in inflammatory cells,4,5 the PDE4D is a plausible candidate gene. PDE4D enzyme activity could play an important role in stroke risk through its effects on inflammation, plaque stability, response to injury, angiogenesis, and susceptibility and response to low grade infections.6,7 The deCODE investigators and others have argued that isoform expression may regulate PDE4D activity based on their relative expression profile.6,8 PDE4D clearly has a complex role in regulating biological activity of tissues in which it is expressed.

A fundamental flaw in the original deCODE article was the lack of independent replication. The deCODE team did survey PDE4D transcript expression in transformed B-cells, which appeared to corroborate the hypothesis that noncoding PDE4D variants are associated both with measurable PDE4D biological activity and ischemic stroke as a major outcome. The limited assay scope (only B-cell lines), the lack of clear relationship to genotype/haplotype, and the known complexity of the autoregulation of PDE4D via the cAMP feedback loop9 argues against drawing general conclusions.

Since this initial report, the stroke genetics community has properly attempted to replicate these findings in other cohorts and populations. There are 10 published follow-up studies by independent groups attempting to reproduce and inform the original findings.9–18 Association studies have tested >55 distinct single-nucleotide proteins (SNPs) in the PDE4D gene although the majority has only been reported in 1 or 2 articles. These studies tested in cohorts of differing ethnicity and ascertainment criteria with nonstandardized adjustments for modifiable and nonmodifiable stroke risk factors. To date, none of these studies have found the same association of the high-risk haplotype and ischemic stroke or any subphenotype.10–15 Several SNPs have shown positive associations at the 0.05 level in some studies, although the effect size has generally been weaker than in the original report.

Adding to the recently burgeoning list of replication studies, in this issue of Stroke Zee et al report the results of a nested case-control study of 259 white men with incident adjudicated stroke drawn from the Physician’s Health Study, matched to an equal number of participants free of stroke or vascular disease, at the time of the primary qualifying event in the cases.16 They included adjustments for main study randomization arm (aspirin or beta carotene), diabetes, and BMI, and tested 9 SNP markers with prior evidence of association in either the deCODE cohort or in the recently published nested case-control analysis of women in the Study of Osteoporotic Fractures (SOF).2,15 After adjusting for traditional stroke risk factors, SNP56 showed nominal significance with ischemic stroke risk (recessive: odds ratio=2.26, 95% CI=1.11 to 4.61; P=0.03). In a stratified analysis of nonhypertensive individuals, SNP45 (dominant: odds ratio=2.24, 95% CI=1.00 to 5.00; P=0.05) and SNP56 (additive: odds ratio=1.77, 95% CI=1.02 to 3.10; P=0.04) showed modest association with increased risk of ischemic stroke. As Zee et al acknowledge, their SNP45 findings of allele A association with ischemic stroke represent a reversal of risk allele from that reported in the original2 and some12,17 but not all follow-up10,11,15,18,19 studies. Interpretation of these results is made more difficult by the observation that 2 groups found the SNP45 locus to be monomorphic in a Japanese and a biracial US population.13,14

The observation that variants in PDE4D manifest reversed direction of effects in differing studies suggests the possibility of spurious associations (Cardon LR, personal communication, 2006). Although hard to quantify, discrete variants that show a consistent effect direction across multiple independent studies20,21 are more likely to be ‘real’ as judged by meta-analysis. Race-specific interactions are sometimes advanced as a possible reason for inconsistency of results across studies, but experience suggests that true associated variants are robust to cross-race effects.22 In other words, race-dependent biological effects in common complex diseases arise from factors that affect the allelic frequencies in the population22 rather than through modulation or reversal of the effect itself.

The results of Zee et al corroborate an emerging view that the overall effects of genetic variation in PDE4D appear to be very modest at best relative to other risk factors in stroke populations defined by the broadest ischemic stroke inclusionary criteria. The difficulty in replicating the primary report of association of genetic variants with a complex disease has sadly been rehearsed many times over, and the possible statistical causes and epidemiological confounders recounted at some length. The initial report of any novel gene association must be treated with measured enthusiasm because the significance-based ranking of association test results across genes and markers inherently leads to bias in the estimated effect size, and concomitant inference of association.

One encouraging aspect of both the Zee study and a recently published analysis by the same authors of the SOF cohort is the suggestive increase in significance of test results for the nonhypertensive stratum, after stratifying the samples by history of hypertension, reflecting the relative importance of this factor in risk for ischemic stroke.23 There are 2 broad explanations for this gene-stratum interaction. Qualitatively, the effective removal of a major risk factor may help to reveal the influence of the underlying genetic variation with reduced confounding of the results ("swamping out" hypothesis). Alternatively, the physiological milieu of patients in this stratum may result in differential importance of PDE4D activity relative to nonstratum patients. In this sense, the analysis parallels approaches used in other complex diseases to disentangle genetic factors from modifiable behavioral or environmental effects.

Although disappointing overall, the Zee et al article offers some useful lessons and suggestions about how to design and perform these studies in the future. We recognize that investigators may have little control over the phenotypes and data that are available in existing stroke cohorts. However, we urge investigators that are planning new studies to include collection of data that will allow for satisfactory adjustment of nongenetic confounding and risk factors. Because common sporadic stroke cases occur in late adulthood, there will be a lifetime of accumulated background risk, and testing selective secondary hypotheses requires correspondingly larger total sample sizes. The stratified analysis of Zee et al was probably underpowered to achieve more compelling significance, given the reasonable estimated odds ratios range 1.6 to 2.2 (at least by complex disease standards) and allele frequencies for the associated SNPs. We remind the community of the following basic principles for conducting genetics studies:

1. Standardize epidemiological and statistical models to incorporate minimal set of recognized risk factors, both modifiable and not.

2. Perform power analyses for all studies, especially negative reports of association, preferably using shrunken estimates of effect size. At a minimum, studies should be powered to allow analysis of the subtype that is most relevant to the study population.

3. Continue to report negative results, particularly well-powered studies, to avoid publication bias.

4. Evaluate study design and results honestly in articles and discussions with reviewers.

5. Characterize study-sample phenotypes, and perform analyses based on rational mechanistic principles to minimize type 1 error, rather than exhaustively testing all possibilities.

Although replication of putative association results is necessary to establish the robustness and generality of a result, and to estimate effect sizes less tainted by biases, we should remember that PDE4D is only the first candidate of a new era in stroke genetics. From a public health perspective, variation in the PDE4D locus seems to contribute only modestly to overall stroke risk in the North American populations tested so far, but with national and international studies reaching maturity, and the availability of very large data sets from whole genome association studies within the next few years, the community will have other candidates and pathways to pursue. Pathways of inflammation, coagulation, cysteine metabolism, atherogenesis, and lipid metabolism may yet yield genes that contribute to a broad stroke outcome or stroke sub(pheno)types. From the existing literature, there are already suggestions that the single extended STRK1 locus may contain multiple loci that contribute to discrete linkage peaks.13,19

So after all of the admiring peeks and compliments, is the King really bare? As the first gene linked to ischemic stroke, the identification of PDE4D has been rightly heralded as a major milestone in the nascent field of stroke genetics. This gene and its associated molecular pathways may still prove to be important in cerebrovascular disease, but will require a concerted systematic and rigorous approach to collecting and analyzing data to disentangle the contributing factors.

Stroke is a youthful member of a widening family of diseases with a complex genetic epidemiology, a family which includes diabetes, obesity, cardiovascular disease, hypertension, asthma, schizophrenia, and autoimmune diseases. If the genetics research on more established complex diseases is any guide, there will be many new suits that are discarded as fashions change, hopefully interspersed with classic and more enduring attire. Realizing these successes may require more finely nuanced hypotheses based on the pathways involved and the physiological milieu in which the genetic variation is exercised. The court and the public await the tale to play out.

Acknowledgments

Sources of Funding

Dr Worrall’s work has been supported in part by National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) grant P50DK0636091 and NINDS grants K08NS45802 and R01NS42733. Dr Mychaleckyj is supported in part by R01NS39987 and R01NS34447.

Disclosure

None.

Footnotes

The opinions in this editorial are not necessarily those of the editors or of the American Heart Association.

References

  1. Andersen HC. Keiserens nye klæder (the emperor’s new clothes). In: Eventyr, fortalte for børn, tredie hefte. Kjøbenhavn: Trykt hos Bianco Luno & Schneider, Forlagt af Universitets-Boghandler C.A. Reitzel; 1837.
  2. Gretarsdottir S, Thorleifsson G, Reynisdottir ST, Manolescu A, Jonsdottir S, Jonsdottir T, Gudmundsdottir T, Bjarnadottir SM, Einarsson OB, Gudjonsdottir HM, Hawkins M, Gudmundsson G, Gudmundsdottir H, Andrason H, Gudmundsdottir AS, Sigurdardottir M, Chou TT, Nahmias J, Goss S, Sveinbjornsdottir S, Valdimarsson EM, Jakobsson F, Agnarsson U, Gudnason V, Thorgeirsson G, Fingerle J, Gurney M, Gudbjartsson D, Frigge ML, Kong A, Stefansson K, Gulcher JR. The gene encoding phosphodiesterase 4D confers risk of ischemic stroke. Nat Genet. 2003; 35: 131–138.[CrossRef][Medline] [Order article via Infotrieve]
  3. Schubert P, Morino T, Miyazaki H, Ogata T, Nakamura Y, Marchini C, Ferroni S. Cascading glia reactions: A common pathomechanism and its differentiated control by cyclic nucleotide signaling. Ann N Y Acad Sci. 2000; 903: 24–33.[Abstract/Free Full Text]
  4. Jacob C, Martin-Chouly C, Lagente V. Type 4 phosphodiesterase-dependent pathways: Role in inflammatory processes. Therapie. 2002; 57: 163–168.[Medline] [Order article via Infotrieve]
  5. Liu H, Maurice DH. Phosphorylation-mediated activation and translocation of the cyclic amp-specific phosphodiesterase PDE4D3 by cyclic amp-dependent protein kinase and mitogen-activated protein kinases. A potential mechanism allowing for the coordinated regulation of PDE4D activity and targeting. J Biol Chem. 1999; 274: 10557–10565.[Abstract/Free Full Text]
  6. Gulcher JR, Gretarsdottir S, Helgadottir A, Stefansson K. Genes contributing to risk for common forms of stroke. Trends Mol Med. 2005; 11: 217–224.[CrossRef][Medline] [Order article via Infotrieve]
  7. Hakonarson H. Role of FLAP and PDE4D in myocardial infarction and stroke: target discovery and future treatment options. Curr Treat Options Cardiovasc Med. 2006; 8: 183–192.[CrossRef][Medline] [Order article via Infotrieve]
  8. Wang D, Deng C, Bugaj-Gaweda B, Kwan M, Gunwaldsen C, Leonard C, Xin X, Hu Y, Unterbeck A, De Vivo M. Cloning and characterization of novel PDE4D isoforms PDE4D6 and PDE4D7. Cell Signal. 2003; 15: 883–891.[CrossRef][Medline] [Order article via Infotrieve]
  9. Hill EV, Houslay MD, Baillie GS. Investigation of extracellular signal-regulated kinase 2 mitogen-activated protein kinase phosphorylation and regulation of activity of PDE4 cyclic adenosine monophosphate-specific phosphodiesterases. Methods Mol Biol. 2005; 307: 225–237.[Medline] [Order article via Infotrieve]
  10. Bevan S, Porteous L, Sitzer M, Markus HS. Phosphodiesterase 4D gene, ischemic stroke, and asymptomatic carotid atherosclerosis. Stroke. 2005; 36: 949–953.[Abstract/Free Full Text]
  11. Kuhlenbaumer G, Berger K, Huge A, Lange E, Kessler C, John U, Funke H, Nabavi DG, Stogbauer F, Ringelstein EB, Stoll M. Evaluation of single nucleotide polymorphisms in the phosphodiesterase 4D gene (PDE4D) and their association with ischaemic stroke in a large German cohort. J Neurol Neurosurg Psychiatry. 2006; 77: 521–524.[Abstract/Free Full Text]
  12. Meschia JF, Brott TG, Brown RD Jr, Crook R, Worrall BB, Kissela B, Brown WM, Rich SS, Case LD, Evans EW, Hague S, Singleton A, Hardy J. Phosphodiesterase 4D and 5-lipoxygenase activating protein in ischemic stroke. Ann Neurol. 2005; 58: 351–361.[CrossRef][Medline] [Order article via Infotrieve]
  13. Nakayama T, Asai S, Sato N, Soma M. Genotype and haplotype association study of the STRK1 region on 5q12 among Japanese: A case-control study. Stroke. 2006; 37: 69–76.[Abstract/Free Full Text]
  14. Woo D, Kaushal R, Kissela B, Sekar P, Wolujewicz M, Pal P, Alwell K, Haverbusch M, Ewing I, Miller R, Kleindorfer D, Flaherty M, Chakraborty R, Deka R, Broderick J. Association of phosphodiesterase 4D with ischemic stroke. A population-based case-control study. Stroke. 2006; 37: 371–376.[Abstract/Free Full Text]
  15. Brophy VH, Ro SK, Rhees BK, Lui LY, Lee JM, Umblas N, Bentley LG, Li J, Cheng S, Browner WS, Erlich HA. Association of phosphodiesterase 4D polymorphisms with ischemic stroke in a us population stratified by hypertension status. Stroke. 2006; 37: 1385–1390.[Abstract/Free Full Text]
  16. Zee RY, Brophy VH, Cheng S, Hegener HH, Erlich HA, Ridker PM. Polymorphisms of the phosphodiesterase 4D, camp-specific (PDE4D) gene and risk of ischemic stroke: A prospective, nested case-control evaluation. Stroke. 2006; 37: 2012–2017.[Abstract/Free Full Text]
  17. van Rijn MJ, Slooter AJ, Schut AF, Isaacs A, Aulchenko YS, Snijders PJ, Kappelle LJ, van Swieten JC, Oostra BA, van Duijn CM. Familial aggregation, the PDE4D gene, and ischemic stroke in a genetically isolated population. Neurology. 2005; 65: 1203–1209.[Abstract/Free Full Text]
  18. Lohmussaar E, Gschwendtner A, Mueller JC, Org T, Wichmann E, Hamann G, Meitinger T, Dichgans M. Alox5ap gene and the PDE4D gene in a Central European population of stroke patients. Stroke. 2005; 36: 731–736.[Abstract/Free Full Text]
  19. Nilsson-Ardnor S, Wiklund PG, Lindgren P, Nilsson AK, Janunger T, Escher SA, Hallbeck B, Stegmayr B, Asplund K, Holmberg D. Linkage of ischemic stroke to the PDE4D region on 5q in a swedish population. Stroke. 2005; 36: 1666–1671.[Abstract/Free Full Text]
  20. Altshuler D, Hirschhorn JN, Klannemark M, Lindgren CM, Vohl MC, Nemesh J, Lane CR, Schaffner SF, Bolk S, Brewer C, Tuomi T, Gaudet D, Hudson TJ, Daly M, Groop L, Lander ES. The common PPARgamma pro12ala polymorphism is associated with decreased risk of type 2 diabetes. Nat Genet. 2000; 26: 76–80.[CrossRef][Medline] [Order article via Infotrieve]
  21. Lohmueller KE, Pearce CL, Pike M, Lander ES, Hirschhorn JN. Meta-analysis of genetic association studies supports a contribution of common variants to susceptibility to common disease. Nat Genet. 2003; 33: 177–182.[CrossRef][Medline] [Order article via Infotrieve]
  22. Ioannidis JP, Ntzani EE, Trikalinos TA. ‘Racial’ differences in genetic effects for complex diseases. Nat Genet. 2004; 36: 1312–1318.[CrossRef][Medline] [Order article via Infotrieve]
  23. Goldstein LB, Adams R, Alberts MJ, Appel LJ, Brass LM, Bushnell CD, Culebras A, Degraba TJ, Gorelick PB, Guyton JR, Hart RG, Howard G, Kelly-Hayes M, Nixon JV, Sacco RL. Primary prevention of ischemic stroke: A guideline from the American Heart Association/American Stroke Association Stroke Council: Cosponsored by the atherosclerotic peripheral vascular disease interdisciplinary working group; cardiovascular nursing council; clinical cardiology council; nutrition, physical activity, and metabolism council; and the quality of care and outcomes research interdisciplinary working group: The American Academy of Neurology affirms the value of this guideline. Stroke. 2006; 37: 1583–1633.[Abstract/Free Full Text]



This article has been cited by other articles:


Home page
 StrokeHome page
E. Touze and P. M. Rothwell
Sex Differences in Heritability of Ischemic Stroke: A Systematic Review and Meta-Analysis
Stroke, January 1, 2008; 39(1): 16 - 23.
[Abstract] [Full Text] [PDF]

Home page
 StrokeHome page
M. Dichgans and R. A. Hegele
Update on the Genetics of Stroke and Cerebrovascular Disease 2006
Stroke, February 1, 2007; 38(2): 216 - 218.
[Full Text] [PDF]

This Article
Right arrow Full Text (PDF)
Right arrow All Versions of this Article:
37/8/1955    most recent
01.STR.0000234048.04053.39v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrow Request Permissions
Citing Articles
Right arrow Citing Articles via HighWire
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by Worrall, B. B.
Right arrow Articles by Mychaleckyj, J. C.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by Worrall, B. B.
Right arrow Articles by Mychaleckyj, J. C.
Right arrowPubmed/NCBI databases
Medline Plus Health Information
*Stroke
Related Collections
Right arrow Genetics of Stroke
Right arrow Risk Factors for Stroke

Stroke Home | Subscriptions | Archives | Feedback | Authors | Help | AHA Journals Home | Search
Copyright © 2006 American Heart Association, Inc. All rights reserved. Unauthorized use prohibited.