Title: Strong Association of the Y402H Variant in Complement Factor H at 1q32 with Susceptibility to Age-Related Macular Degeneration
Abstract: Using a large sample of cases and controls from a single center, we show that a T→C substitution in exon 9 (Y402H) of the complement factor H gene is strongly associated with susceptibility to age-related macular degeneration, the most common cause of blindness in the elderly. Frequency of the C allele was 0.61 in cases, versus 0.34 in age-matched controls (P<1×10−24). Genotype frequencies also differ markedly between cases and controls (χ2=112.68 [2 degrees of freedom]; P<1×10−24). A multiplicative model fits the data well, and we estimate the population frequency of the high-risk C allele to be 0.39 (95% confidence interval 0.36–0.42) and the genotype relative risk to be 2.44 (95% confidence interval 2.08–2.83) for TC heterozygotes and 5.93 (95% confidence interval 4.33–8.02) for CC homozygotes. Using a large sample of cases and controls from a single center, we show that a T→C substitution in exon 9 (Y402H) of the complement factor H gene is strongly associated with susceptibility to age-related macular degeneration, the most common cause of blindness in the elderly. Frequency of the C allele was 0.61 in cases, versus 0.34 in age-matched controls (P<1×10−24). Genotype frequencies also differ markedly between cases and controls (χ2=112.68 [2 degrees of freedom]; P<1×10−24). A multiplicative model fits the data well, and we estimate the population frequency of the high-risk C allele to be 0.39 (95% confidence interval 0.36–0.42) and the genotype relative risk to be 2.44 (95% confidence interval 2.08–2.83) for TC heterozygotes and 5.93 (95% confidence interval 4.33–8.02) for CC homozygotes. Age-related macular degeneration (AMD) (ARMD1 [MIM 603075]), the leading cause of untreatable blindness among the elderly in Western populations, is a clinically heterogeneous and genetically complex disease with multiple genetic and environmental risk factors (Age-Related Eye Disease Study Research Group Age-Related Eye Disease Study Research Group, 2000Age-Related Eye Disease Study Research Group Risk factors associated with age-related macular degeneration. A case-control study in the age-related eye disease study: Age-Related Eye Disease Study Report Number 3.Ophthalmology. 2000; 107: 2224-2232Abstract Full Text Full Text PDF PubMed Scopus (634) Google Scholar). Mutations in several genes (e.g., ABCA4 [MIM 601691], TIMP3 [MIM 188826], RDS/peripherin [MIM 179605], and ELOVL4 [MIM 605512]) can cause early-onset macular diseases, but they do not appear to contribute significantly to AMD susceptibility (Stone et al. Stone et al., 2001Stone EM Sheffield VC Hageman GS Molecular genetics of age-related macular degeneration.Hum Mol Genet. 2001; 10: 2285-2292Crossref PubMed Scopus (74) Google Scholar). Particularly interesting are the fibulin-3 gene (MIM 601548) and related genes. Fibulin-3 mutations underlie drusen formation in Doyne honeycomb retinal dystrophy (MIM 126600), a disease that is phenotypically similar to AMD (Stone et al. Stone et al., 1999Stone EM Lotery AJ Munier FL Heon E Piguet B Guymer RH Vandenburgh K Cousin P Nishimura D Swiderski RE Silvestri G Mackey DA Hageman GS Bird AC Sheffield VC Schorderet DF A single EFEMP1 mutation associated with both Malattia Leventinese and Doyne honeycomb retinal dystrophy.Nat Genet. 1999; 22: 199-202Crossref PubMed Scopus (369) Google Scholar; Marmorstein et al. Marmorstein et al., 2002Marmorstein LY Munier FL Arsenijevic Y Schorderet DF McLaughlin PJ Chung D Traboulsi E Marmorstein AD Aberrant accumulation of EFEMP1 underlies drusen formation in malattia leventinese and age-related macular degeneration.Proc Natl Acad Sci USA. 2002; 99: 13067-13072Crossref PubMed Scopus (164) Google Scholar). A mutation screen of five other fibulin genes detected missense mutations in fibulin-5 (MIM 604580) in 1.7% of patients with AMD (Stone et al. Stone et al., 2004Stone EM Braun TA Russell SR Kuehn MH Lotery AJ Moore PA Eastman CG Casavant TL Sheffield VC Missense variations in the fibulin 5 gene and age-related macular degeneration.N Engl J Med. 2004; 351: 346-353Crossref PubMed Scopus (263) Google Scholar). In addition, a fibulin-6 (MIM 608548) variant has been reported to cosegregate with the ARMD1 locus in one large pedigree (Schultz et al. Schultz et al., 2003Schultz DW Klein ML Humpert AJ Luzier CW Persun V Schain M Mahan A Runckel C Cassera M Vittal V Doyle TM Martin TM Weleber RG Francis PJ Acott TS Analysis of the ARMD1 locus: evidence that a mutation in HEMICENTIN-1 is associated with age-related macular degeneration in a large family.Hum Mol Genet. 2003; 12: 3315-3323Crossref PubMed Scopus (158) Google Scholar). However, this change does not appear to play a significant role in AMD (Abecasis et al. Abecasis et al., 2004Abecasis GR Yashar BM Zhao Y Ghiasvand NM Zareparsi S Branham KE Reddick AC Trager EH Yoshida S Bahling J Filippova E Elner S Johnson MW Vine AK Sieving PA Jacobson SG Richards JE Swaroop A Age-related macular degeneration: a high-resolution genome scan for susceptibility loci in a population enriched for late-stage disease.Am J Hum Genet. 2004; 74: 482-494Abstract Full Text Full Text PDF PubMed Scopus (139) Google Scholar; Hayashi et al. Hayashi et al., 2004Hayashi M Merriam JE Klaver CC Zernant J Bergen AA Smith RT Chang S Merriam JC Allikmets R Evaluation of the ARMD1 locus on 1q25-31 in patients with age-related maculopathy: genetic variation in laminin genes and in exon 104 of HEMICENTIN-1.Ophthalmic Genet. 2004; 25: 111-119Crossref PubMed Scopus (30) Google Scholar; Iyengar et al. Iyengar et al., 2004Iyengar SK Song D Klein BE Klein R Schick JH Humphrey J Millard C Liptak R Russo K Jun G Lee KE Fijal B Elston RC Dissection of genomewide-scan data in extended families reveals a major locus and oligogenic susceptibility for age-related macular degeneration.Am J Hum Genet. 2004; 74: 20-39Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar). Linkage studies have suggested several chromosomal regions that may harbor AMD susceptibility genes. Klein and colleagues (Klein et al., 1998Klein ML Schultz DW Edwards A Matise TC Rust K Berselli CB Trzupek K Weleber RG Ott J Wirtz MK Acott TS Age-related macular degeneration: clinical features in a large family and linkage to chromosome 1q.Arch Ophthalmol. 1998; 116: 1082-1088Crossref PubMed Scopus (201) Google Scholar) were the first to map a susceptibility locus (ARMD1) to chromosome 1q25-q31 in a large pedigree with AMD. Since then, many studies have been performed, and, overall, their results provide support for susceptibility loci on several chromosomes, including chromosomes 1q, 9q, 10q, and 22q (Weeks et al. Weeks et al., 2000Weeks DE Conley YP Mah TS Paul TO Morse L Ngo-Chang J Dailey JP Ferrell RE Gorin MB A full genome scan for age-related maculopathy.Hum Mol Genet. 2000; 9: 1329-1349Crossref PubMed Scopus (111) Google Scholar, Weeks et al., 2004Weeks DE Conley YP Tsai HJ Mah TS Schmidt S Postel EA Agarwal A Haines JL Pericak-Vance MA Rosenfeld PJ Paul TO Eller AW Morse LS Dailey JP Ferrell RE Gorin MB Age-related maculopathy: a genomewide scan with continued evidence of susceptibility loci within the 1q31, 10q26, and 17q25 regions.Am J Hum Genet. 2004; 75: 174-189Abstract Full Text Full Text PDF PubMed Scopus (150) Google Scholar; Majewski et al. Majewski et al., 2003Majewski J Schultz DW Weleber RG Schain MB Edwards AO Matise TC Acott TS Ott J Klein ML Age-related macular degeneration: a genome scan in extended families.Am J Hum Genet. 2003; 73: 540-550Abstract Full Text Full Text PDF PubMed Scopus (160) Google Scholar; Seddon et al. Seddon et al., 2003Seddon JM Santangelo SL Book K Chong S Cote J A genomewide scan for age-related macular degeneration provides evidence for linkage to several chromosomal regions.Am J Hum Genet. 2003; 73: 780-790Abstract Full Text Full Text PDF PubMed Scopus (174) Google Scholar; Abecasis et al. Abecasis et al., 2004Abecasis GR Yashar BM Zhao Y Ghiasvand NM Zareparsi S Branham KE Reddick AC Trager EH Yoshida S Bahling J Filippova E Elner S Johnson MW Vine AK Sieving PA Jacobson SG Richards JE Swaroop A Age-related macular degeneration: a high-resolution genome scan for susceptibility loci in a population enriched for late-stage disease.Am J Hum Genet. 2004; 74: 482-494Abstract Full Text Full Text PDF PubMed Scopus (139) Google Scholar; Iyengar et al. Iyengar et al., 2004Iyengar SK Song D Klein BE Klein R Schick JH Humphrey J Millard C Liptak R Russo K Jun G Lee KE Fijal B Elston RC Dissection of genomewide-scan data in extended families reveals a major locus and oligogenic susceptibility for age-related macular degeneration.Am J Hum Genet. 2004; 74: 20-39Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar; Schmidt et al. Schmidt et al., 2004Schmidt S Scott WK Postel EA Agarwal A Hauser ER De La Paz MA Gilbert JR Weeks DE Gorin MB Haines JL Pericak-Vance MA Ordered subset linkage analysis supports a susceptibility locus for age-related macular degeneration on chromosome 16p12.BMC Genet. 2004; 5: 18Crossref PubMed Scopus (42) Google Scholar). Association studies have also been performed, and some of the identified loci appear to contribute to disease susceptibility. For example, an association between AMD and allelic variants of apolipoprotein E (APOE [MIM 107741]) has been widely documented, with the APOE-ɛ4 allele linked to lower risk of disease and the APOE-ɛ2 allele linked to higher risk (Klaver et al. Klaver et al., 1998Klaver CC Kliffen M van Duijn CM Hofman A Cruts M Grobbee DE van Broeckhoven C de Jong PT Genetic association of apolipoprotein E with age-related macular degeneration.Am J Hum Genet. 1998; 63: 200-206Abstract Full Text Full Text PDF PubMed Scopus (343) Google Scholar; Schmidt et al. Schmidt et al., 2002Schmidt S Klaver C Saunders A Postel E De La Paz M Agarwal A Small K Udar N Ong J Chalukya M Nesburn A Kenney C Domurath R Hogan M Mah T Conley Y Ferrell R Weeks D de Jong PT van Duijn C Haines J Pericak-Vance M Gorin M A pooled case-control study of the apolipoprotein E (APOE) gene in age-related maculopathy.Ophthalmic Genet. 2002; 23: 209-223Crossref PubMed Scopus (119) Google Scholar; Baird et al. Baird et al., 2004Baird PN Guida E Chu DT Vu HT Guymer RH The epsilon2 and epsilon4 alleles of the apolipoprotein gene are associated with age-related macular degeneration.Invest Ophthalmol Vis Sci. 2004; 45: 1311-1315Crossref PubMed Scopus (159) Google Scholar; Zareparsi et al. Zareparsi et al., 2004Zareparsi S Reddick AC Branham KE Moore KB Jessup L Thoms S Smith-Wheelock M Yashar BM Swaroop A Association of apolipoprotein E alleles with susceptibility to age-related macular degeneration in a large cohort from a single center.Invest Ophthalmol Vis Sci. 2004; 45: 1306-1310Crossref PubMed Scopus (107) Google Scholar). Recently, we reported an association between increased risk of AMD and the D299G variation in toll-like receptor 4 (TLR4 [MIM 603030]), a protein involved in innate immunity and phagocytosis by retinal pigment epithelium (Zareparsi et al. Zareparsi et al., 2005Zareparsi S Buraczynska M Branham KE Shah S Eng D Li M Pawar H Yashar BM Moroi SE Lichter PR Petty HR Richards JE Abecasis GR Elner VM Swaroop A Toll-like receptor 4 variant D299G is associated with susceptibility to age-related macular degeneration.Hum Mol Genet. 2005; (electronically published April 13, 2005; accessed May 9, 2005)(http://hmg.oupjournals.org/cgi/reprint/ddi154v1)Google Scholar). Despite these advances, the alleles that account for most of the genetic susceptibility to AMD remain undiscovered. Recently, three independent studies have suggested that a polymorphism (Y402H) in the complement factor H gene (CFH [MIM 134370]) makes a substantial contribution to AMD susceptibility (Y402H has a T→C substitution at nucleotide 1277 in exon 9, which results in a tyrosine→histidine change). All three studies relied on linkage disequilibrium in the region and advances in SNP genotyping for gene identification (Abecasis et al. Abecasis et al., 2005Abecasis GR Ghosh D Nichols TE Linkage disequilibrium: ancient history drives the new genetics.Hum Hered. 2005; 59: 118-124Crossref PubMed Scopus (38) Google Scholar). CFH maps to a region of chromosome 1q where several genome scans showed substantial evidence for linkage. One study (Klein et al. Klein et al., 2005Klein RJ Zeiss C Chew EY Tsai JY Sackler RS Haynes C Henning AK Sangiovanni JP Mane SM Mayne ST Bracken MB Ferris FL Ott J Barnstable C Hoh J Complement factor H polymorphism in age-related macular degeneration.Science. 2005; 308: 385-389Crossref PubMed Scopus (3301) Google Scholar), a genomewide association scan of 96 AMD cases and 50 controls by use of an Affymetrix 100K chip, identified two neighboring SNPs that were significantly associated with AMD. Another study (Edwards et al. Edwards et al., 2005Edwards AO Ritter 3rd, R Abel KJ Manning A Panhuysen C Farrer LA Complement factor H polymorphism and age-related macular degeneration.Science. 2005; 308: 421-424Crossref PubMed Scopus (1968) Google Scholar) examined noncoding SNPs across 14 Mb of the ARMD1 locus on chromosome 1q in a sample of 224 cases and 134 controls; genotyping of 14 SNPs spanning CFH was performed in a larger sample. The third study (Haines et al. Haines et al., 2005Haines JL Hauser MA Schmidt S Scott WK Olson LM Gallins P Spencer KL Kwan SY Noureddine M Gilbert JR Schnetz-Boutaud N Agarwal A Postel EA Pericak-Vance MA Complement factor H variant increases the risk of age-related macular degeneration.Science. 2005; 308: 419-421Crossref PubMed Scopus (1973) Google Scholar) also focused on examination of SNPs distributed across the ARMD1 locus, but it included a sample of 495 unrelated cases, 185 controls, and 182 families. In each study, initial associations were followed by additional genotyping that eventually led to the identification of a peak of association, which suggested the CFH-Y402H (C/T) variant as the susceptibility allele. These studies reported odds ratios (ORs) for AMD ranging between 2.4 and 4.6 for carriers of the C allele and between 3.3 and 7.4 for CC homozygotes (Edwards et al. Edwards et al., 2005Edwards AO Ritter 3rd, R Abel KJ Manning A Panhuysen C Farrer LA Complement factor H polymorphism and age-related macular degeneration.Science. 2005; 308: 421-424Crossref PubMed Scopus (1968) Google Scholar; Haines et al. Haines et al., 2005Haines JL Hauser MA Schmidt S Scott WK Olson LM Gallins P Spencer KL Kwan SY Noureddine M Gilbert JR Schnetz-Boutaud N Agarwal A Postel EA Pericak-Vance MA Complement factor H variant increases the risk of age-related macular degeneration.Science. 2005; 308: 419-421Crossref PubMed Scopus (1973) Google Scholar; Klein et al. Klein et al., 2005Klein RJ Zeiss C Chew EY Tsai JY Sackler RS Haynes C Henning AK Sangiovanni JP Mane SM Mayne ST Bracken MB Ferris FL Ott J Barnstable C Hoh J Complement factor H polymorphism in age-related macular degeneration.Science. 2005; 308: 385-389Crossref PubMed Scopus (3301) Google Scholar). Independent replication studies are required to accurately assess the contribution of the associated alleles to disease susceptibility, because initial reports of association are vulnerable to a “winner’s curse” effect, which can produce overestimates of the effect size (Goring et al. Goring et al., 2001Goring HH Terwilliger JD Blangero J Large upward bias in estimation of locus-specific effects from genomewide scans.Am J Hum Genet. 2001; 69: 1357-1369Abstract Full Text Full Text PDF PubMed Scopus (386) Google Scholar; Lohmueller et al. Lohmueller et al., 2003Lohmueller 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: 177-182Crossref PubMed Scopus (1583) Google Scholar). We used a large sample of cases (N=616) and controls (N=275), collected at the Kellogg Eye Center in Ann Arbor, MI, to provide independent estimates of the effect of this common variant (CFH-Y402H) on AMD susceptibility. A majority of patients with AMD had late-stage AMD that presented as choroidal neovascularization (CNV [N=238]), geographic atrophy (GA [N=143]), or both CNV and GA (N=133). The remaining patients had large macular drusen (LMD) in both eyes (N=102) (Abecasis et al. Abecasis et al., 2004Abecasis GR Yashar BM Zhao Y Ghiasvand NM Zareparsi S Branham KE Reddick AC Trager EH Yoshida S Bahling J Filippova E Elner S Johnson MW Vine AK Sieving PA Jacobson SG Richards JE Swaroop A Age-related macular degeneration: a high-resolution genome scan for susceptibility loci in a population enriched for late-stage disease.Am J Hum Genet. 2004; 74: 482-494Abstract Full Text Full Text PDF PubMed Scopus (139) Google Scholar; Zareparsi et al. Zareparsi et al., 2004Zareparsi S Reddick AC Branham KE Moore KB Jessup L Thoms S Smith-Wheelock M Yashar BM Swaroop A Association of apolipoprotein E alleles with susceptibility to age-related macular degeneration in a large cohort from a single center.Invest Ophthalmol Vis Sci. 2004; 45: 1306-1310Crossref PubMed Scopus (107) Google Scholar). Control individuals were at least 68 years old and did not present any evidence of AMD in either eye after ophthalmic examination. All patients and controls reported their ethnicity as “white, not of Hispanic origin” and were recruited after informed consent. The human-genetics investigations described here were approved by the University of Michigan institutional review board. Genotyping was performed without knowledge of disease status. As shown in table 1, we detected a significantly higher frequency of the C allele in patients with AMD than in controls (0.61 vs. 0.34; χ2 = 110.96 [1 df]; P<1×10−24). Genotype frequencies are also significantly different in affected and unaffected individuals (χ2=112.68 [2 df]; P<1×10−24). OR calculations show that individuals carrying at least one copy of the C allele have a 4.36-fold increase in the risk of AMD (95% CI 3.13–6.08), whereas homozygous CC individuals exhibit a 5.52-fold increase in the risk of developing AMD (95% CI 3.54–8.59). Our results are within the range reported by the original studies (Edwards et al. Edwards et al., 2005Edwards AO Ritter 3rd, R Abel KJ Manning A Panhuysen C Farrer LA Complement factor H polymorphism and age-related macular degeneration.Science. 2005; 308: 421-424Crossref PubMed Scopus (1968) Google Scholar; Haines et al. Haines et al., 2005Haines JL Hauser MA Schmidt S Scott WK Olson LM Gallins P Spencer KL Kwan SY Noureddine M Gilbert JR Schnetz-Boutaud N Agarwal A Postel EA Pericak-Vance MA Complement factor H variant increases the risk of age-related macular degeneration.Science. 2005; 308: 419-421Crossref PubMed Scopus (1973) Google Scholar; Klein et al. Klein et al., 2005Klein RJ Zeiss C Chew EY Tsai JY Sackler RS Haynes C Henning AK Sangiovanni JP Mane SM Mayne ST Bracken MB Ferris FL Ott J Barnstable C Hoh J Complement factor H polymorphism in age-related macular degeneration.Science. 2005; 308: 385-389Crossref PubMed Scopus (3301) Google Scholar), and they validate the gene-dosage effect reported in two of the studies (Haines et al. Haines et al., 2005Haines JL Hauser MA Schmidt S Scott WK Olson LM Gallins P Spencer KL Kwan SY Noureddine M Gilbert JR Schnetz-Boutaud N Agarwal A Postel EA Pericak-Vance MA Complement factor H variant increases the risk of age-related macular degeneration.Science. 2005; 308: 419-421Crossref PubMed Scopus (1973) Google Scholar; Klein et al. Klein et al., 2005Klein RJ Zeiss C Chew EY Tsai JY Sackler RS Haynes C Henning AK Sangiovanni JP Mane SM Mayne ST Bracken MB Ferris FL Ott J Barnstable C Hoh J Complement factor H polymorphism in age-related macular degeneration.Science. 2005; 308: 385-389Crossref PubMed Scopus (3301) Google Scholar). Inclusion of age and sex as covariates in the logistic regression analysis did not affect the conclusions. Homozygous individuals for the putative risk allele were more common in all subtypes of AMD than in controls; specifically, those homozygous for the C allele included 38% of patients with GA, 34% of those with CNV, and 33% of those with LMD in both eyes, as compared with only 9% of control individuals. Interestingly, the homozygous genotype (CC) was more common in patients with a family history of AMD (38% of 261 cases) than in those without a family history (33% of 308 cases), a difference that was not statistically significant (P>.05). Finally, we note that the diagnosis of AMD occurred earlier for patients with at least one copy of the risk allele (mean in years [± SD] 70.9 ± 8.6) than for those without the risk allele (73.7 ± 9.2; P=.01).Table 1Genotypic and Allele Frequencies for the T→C (Y402H) Variation in CFH Exon 9No. (Frequency) of Genotypeor Allele inGenotypeor AlleleIndividuals with AMD [N=616]Controls [N=275)]TT86 (.14)114 (.415)TC311 (.50)136 (.495)CC219 (.36)25 (.09)T allele483 (.39)364 (.66)C allele749 (.61)186 (.34) Open table in a new tab To characterize the contribution of the Y402H polymorphism to AMD susceptibility, we fitted a series of genetic models to the data by maximum-likelihood estimation (results summarized in table 2). Model fitting was performed using the software and methods of Li et al. (Li et al., 2005Li M Boehnke M Abecasis GR Joint modeling of linkage and association: identifying SNPs responsible for a linkage signal.Am J Hum Genet. 2005; 76: 934-949Abstract Full Text Full Text PDF PubMed Scopus (91) Google Scholar). We performed our analysis with the assumption of a disease prevalence (K) of 0.20 (table 2), which is compatible with published estimates for elderly populations >70 years of age (Friedman et al. Friedman et al., 2004Friedman DS O’Colmain BJ Munoz B Tomany SC McCarty C de Jong PT Nemesure B Mitchell P Kempen J Prevalence of age-related macular degeneration in the United States.Arch Ophthalmol. 2004; 122: 564-572Crossref PubMed Scopus (68) Google Scholar), and without constraints on disease prevalence (table 2). With the use of a model with constrained prevalence (K=0.20), the data suggest that the population frequency of the C allele is 0.39 (95% CI 0.36–0.42) and that the relative risk is 2.81 (95% CI 2.17–3.65) for TC heterozygotes and 6.30 (95% CI 4.53–8.72) for CC homozygotes. We also used the Akaike Information Criterium (AIC) to compare all models, including those with constrained and unconstrained prevalence, and to select the best-fitting genetic model. Our results suggest a multiplicative model—with K=0.20, a disease-allele frequency of 0.39 (95% CI 0.36–0.42), and genotype relative risks of 2.44 (95% CI 2.08–2.83) for TC heterozygotes and 5.93 (95% CI 4.33–8.02) for CC homozygotes—as the most parsimonious model. The fitted log likelihood was ln(L)=−865.75 for the multiplicative model with K=0.20 (two parameters, one for the genotype relative risk and another for the disease-allele frequency), versus ln(L)=−864.86 for an unconstrained model (four parameters, corresponding to three penetrances and one disease-allele frequency) and ln(L)=−923.18 for a model under the assumption of no contribution to disease susceptibility (one parameter, corresponding to the marker-allele frequency). Using this multiplicative model, we estimate the contribution of this allele to sibling-specific recurrence risk of AMD to be λs=1.21 and the population-attributable fraction to be 0.62. This is the locus-specific λs, which can be calculated as a function of penetrances and disease-allele frequencies by use of the formulas of Risch (Risch, 1990Risch N Linkage strategies for genetically complex traits. I. Multilocus models.Am J Hum Genet. 1990; 46: 222-228PubMed Google Scholar). The model predicts frequencies of 0.43, 0.47, and 0.10 among controls and 0.15, 0.48, 0.37 among cases for the TT, TC, and CC genotypes, respectively; the predicted values closely match the observed frequencies (see table 1) (goodness-of-fit χ2=2.61 [2 df], not significant). An additive model also fits the data well, but dominant or recessive models are excluded. The agreement between our fitted model and observed genotype counts suggests that population stratification is not a major concern (Wittke-Thompson et al. Wittke-Thompson et al., 2005Wittke-Thompson JK Pluzhnikov A Cox NJ Rational inferences about departures from Hardy-Weinberg equilibrium.Am J Hum Genet. 2005; 76: 967-986Abstract Full Text Full Text PDF PubMed Scopus (318) Google Scholar), a conclusion consistent with our analysis of previous genome-scan data.Table 2Comparison of Fitted Genetic ModelsPrevalence and Model (No. of Parameters)ln(L)P(C)aEstimated frequency of allele C.f(TT)bEstimated probability of disease for genotype.f(TC)bEstimated probability of disease for genotype.f(CC)bEstimated probability of disease for genotype.GRR1cGRR1=f(TC)/f(TT).GRR2dGRR2=f(CC)/f(TT).KAttributable FractionλsConstrained to K=.20: No effect (1)−923.18.52.20.20.2011.20…… General (3)−864.86.39.08.21.472.816.30.20.621.21 MultiplicativeeConstraint: GRR2=GRR12. (2)−865.75fThe best-fitting model, selected using the AIC..39.08.20.492.445.93.20.591.21 AdditivegConstraint: GRR1-1=GRR2-GRR1. (2)−869.14.41.07.23.383.055.10.20.631.14 DominanthConstraint: GRR1=GRR2. (2)−893.28.46.09.24.242.622.62.20.531.05 RecessiveiContraint: GRR1=1.0. (2)−897.67.46.16.16.361.002.24.20.211.07Unconstrained: No effect (1)−923.18.52NANANA11NA…… General (4)−864.46.49.30.57.831.882.77.56.461.06 MultiplicativeeConstraint: GRR2=GRR12. (3)−865.54.43.15.31.662.104.40.32.531.14 AdditivegConstraint: GRR1-1=GRR2-GRR1. (3)−864.46.49.30.57.831.882.76.56.461.06 DominanthConstraint: GRR1=GRR2. (3)−884.30.52.41.75.751.831.83.68.391.02 RecessiveiContraint: GRR1=1.0. (3)−884.77.53.63.63.911.001.43.71.111.01Note.—NA = not applicable.a Estimated frequency of allele C.b Estimated probability of disease for genotype.c GRR1=f(TC)/f(TT).d GRR2=f(CC)/f(TT).e Constraint: GRR2=GRR12.f The best-fitting model, selected using the AIC.g Constraint: GRR1-1=GRR2-GRR1.h Constraint: GRR1=GRR2.i Contraint: GRR1=1.0. Open table in a new tab Note.— NA = not applicable. CFH plays an essential role in regulation of complement activation, a major component of innate immunity against microbial infection. This regulation is achieved because CFH can bind to C3b (generated by cleavage of the α-chain of complement 3 [C3]), leading to the production of terminal C5b-9 complex (Giannakis et al. Giannakis et al., 2003Giannakis E Jokiranta TS Male DA Ranganathan S Ormsby RJ Fischetti VA Mold C Gordon DL A common site within factor H SCR 7 responsible for binding heparin, C-reactive protein and streptococcal M protein.Eur J Immunol. 2003; 33: 962-969Crossref PubMed Scopus (136) Google Scholar). Many proteins of the complement system, including C5b-9 complex, have been detected in drusen from the eyes of patients with AMD (Mullins et al. Mullins et al., 2000Mullins RF Russell SR Anderson DH Hageman GS Drusen associated with aging and age-related macular degeneration contain proteins common to extracellular deposits associated with atherosclerosis, elastosis, amyloidosis, and dense deposit disease.FASEB J. 2000; 14: 835-846Crossref PubMed Scopus (684) Google Scholar; Hageman et al. Hageman et al., 2001Hageman GS Luthert PJ Victor Chong NH Johnson LV Anderson DH Mullins RF An integrated hypothesis that considers drusen as biomarkers of immune-mediated processes at the RPE-Bruch’s membrane interface in aging and age-related macular degeneration.Prog Retin Eye Res. 2001; 20: 705-732Crossref PubMed Scopus (1029) Google Scholar; Johnson et al. Johnson et al., 2001Johnson LV Leitner WP Staples MK Anderson DH Complement activation and inflammatory processes in drusen formation and age related macular degeneration.Exp Eye Res. 2001; 73: 887-896Crossref PubMed Scopus (476) Google Scholar). CFH has three binding sites for C3b and additional binding sites for heparin and C-reactive protein (CRP). The Y402H change is expected to alter these interactions, since it is located within the cluster of positively charged amino acids implicated in the binding of CRP and heparin (Giannakis et al. Giannakis et al., 2003Giannakis E Jokiranta TS Male DA Ranganathan S Ormsby RJ Fischetti VA Mold C Gordon DL A common site within factor H SCR 7 responsible for binding heparin, C-reactive protein and streptococcal M protein.Eur J Immunol. 2003; 33: 962-969Crossref PubMed Scopus (136) Google Scholar). Notably, associations have been reported between AMD and increased levels of CRP (Seddon et al. Seddon et al., 2004Seddon JM Gensler G Milton RC Klein ML Rifai N Association between C-reactive protein and age-related macular degeneration.JAMA. 2004; 291: 704-710Crossref PubMed Scopus (348) Google Scholar) and between AMD and a polymorphism in TLR4, a key gene involved in innate immunity (Zareparsi et al. Zareparsi et al., 2005Zareparsi S Buraczynska M Branham KE Shah S Eng D Li M Pawar H Yashar BM Moroi SE Lichter PR Petty HR Richards JE Abecasis GR Elner VM Swaroop A Toll-like receptor 4 variant D299G is associated with susceptibility to age-related macular degeneration.Hum Mol Genet. 2005; (electronically published April 13, 2005; accessed May 9, 2005)(http://hmg.oupjournals.org/cgi/reprint/ddi154v1)Google Scholar). Hence, it is possible that certain microbial infections may be environmental triggers for AMD pathogenesis. In summary, our data provide strong evidence for the Y402H variant being a common susceptibility allele for AMD. It is possible that another allele in strong disequilibrium with Y402H may cause disease susceptibility; this hypothesis can be tested only by evaluation of all polymorphisms and/or mechanistic functional evidence to explain the role of the Y402H variant. Our resequencing of CFH exon 9 (∼500 bp) in all cases and controls did not identify any additional nearby coding variants. It will also be important to determine if the CFH-Y402H variant can explain the chromosome 1q linkage signal that is observed in independent genome scans (Klein et al. Klein et al., 1998Klein ML Schultz DW Edwards A Matise TC Rust K Berselli CB Trzupek K Weleber RG Ott J Wirtz MK Acott TS Age-related macular degeneration: clinical features in a large family and linkage to chromosome 1q.Arch Ophthalmol. 1998; 116: 1082-1088Crossref PubMed Scopus (201) Google Scholar; Majewski et al. Majewski et al., 2003Majewski J Schultz DW Weleber RG Schain MB Edwards AO Matise TC Acott TS Ott J Klein ML Age-related macular degeneration: a genome scan in extended families.Am J Hum Genet. 2003; 73: 540-550Abstract Full Text Full Text PDF PubMed Scopus (160) Google Scholar; Seddon et al. Seddon et al., 2003Seddon JM Santangelo SL Book K Chong S Cote J A genomewide scan for age-related macular degeneration provides evidence for linkage to several chromosomal regions.Am J Hum Genet. 2003; 73: 780-790Abstract Full Text Full Text PDF PubMed Scopus (174) Google Scholar; Abecasis et al. Abecasis et al., 2004Abecasis GR Yashar BM Zhao Y Ghiasvand NM Zareparsi S Branham KE Reddick AC Trager EH Yoshida S Bahling J Filippova E Elner S Johnson MW Vine AK Sieving PA Jacobson SG Richards JE Swaroop A Age-related macular degeneration: a high-resolution genome scan for susceptibility loci in a population enriched for late-stage disease.Am J Hum Genet. 2004; 74: 482-494Abstract Full Text Full Text PDF PubMed Scopus (139) Google Scholar; Iyengar et al. Iyengar et al., 2004Iyengar SK Song D Klein BE Klein R Schick JH Humphrey J Millard C Liptak R Russo K Jun G Lee KE Fijal B Elston RC Dissection of genomewide-scan data in extended families reveals a major locus and oligogenic susceptibility for age-related macular degeneration.Am J Hum Genet. 2004; 74: 20-39Abstract Full Text Full Text PDF PubMed Scopus (154) Google Scholar; Weeks et al. Weeks et al., 2004Weeks DE Conley YP Tsai HJ Mah TS Schmidt S Postel EA Agarwal A Haines JL Pericak-Vance MA Rosenfeld PJ Paul TO Eller AW Morse LS Dailey JP Ferrell RE Gorin MB Age-related maculopathy: a genomewide scan with continued evidence of susceptibility loci within the 1q31, 10q26, and 17q25 regions.Am J Hum Genet. 2004; 75: 174-189Abstract Full Text Full Text PDF PubMed Scopus (150) Google Scholar). Although CFH and TLR4 are the first major AMD susceptibility genes to be identified, comprehensive studies of genetic variations are expected to lead to the identification of additional variants that contribute to this complex and debilitating disease. We thank all the individuals who participated in this study, and we are grateful to numerous ophthalmologists and clinical staff for insights and assistance. This research was supported by grants from the National Institutes of Health (F32-EY014085, R01-EY015771, P30-EY007003, and K25-HG000060), the Foundation Fighting Blindness, the Macula Vision Research Foundation, the Elmer and Sylvia Sramek Foundation, Research to Prevent Blindness, and the Harold F. Falls Collegiate Professorship.