Linkage Replication of theMYP12Locus in Common Myopia

PURPOSE

Myopia is a common disorder with a large public health impact. Although 12 myopia loci have been reported and heterogeneity for high myopia loci have been demonstrated, replication of high-myopia loci with a common myopia phenotype has not been successful. This study reports the successful replication of MYP12 in three large, multigenerational families with autosomal dominant (AD) common myopia (spherical equivalent [SphE] </= -0.50 D).

METHODS

These families contained 49 participants (35 affected). The average spherical equivalent was -2.76 D (range, -0.50 to -10.25 D), average axial length was 24.52 mm (range, 23.05-27.11 mm), and average keratometry was 43.21 D (range, 39.12-47.31 D). Only five individuals in the three families presented with myopia of SphE </= -6.00 D. Glaucoma, keratoconus, lenticonus, and dislocated lens were not present in any study participants. A genomewide scan was performed using a mapping set with 400 markers at approximately 10 cM coverage. Merlin software was used for multipoint linkage analysis based on an AD model with a penetrance of 0.9 and disease allele frequency of 0.013.

RESULTS

Significant linkage with a multipoint parametric LOD score of 3.428 (P = 0.000035) and a multipoint nonparametric (Kong and Cox) LOD score of 2.37 (empiric P < 0.001) was obtained on 2q37.1, with a 1-LOD support interval that overlapped the previously reported MYP12 locus for high myopia.

CONCLUSIONS

This study provided evidence that some high-myopia loci may contribute to all degrees of myopia and indicated the likely location of a myopia gene for the low/moderate as well as the high form of myopia.

Evaluation of Accuracy in Proband-Reported Family History and Its Determinants: The Genes in Myopia Family Study

PURPOSE

Proband-reported family histories are widely used in epidemiological and genetic studies. The accuracy of these reports may have significant effects on the intended outcome, particularly in genetic studies. This study aims to determine the accuracy of proband-reported family history of myopia and to assess whether demographic or clinical factors are predictive of an accurate history.

METHODS

In 2004 to 2005, the study recruited 120 myopic probands (< or = -0.50 D spherical equivalent in both eyes) aged 18 to 72 years and 358 nuclear family members residing within Victoria, Australia as part of the Genes in Myopia (GEM) family study. Data collection used an examiner-administered questionnaire with an ocular examination. Proband-reported family history of myopia was evaluated for agreement with ophthalmic examination results of family members.

RESULTS

The statistical measures of accuracy used in this report were sensitivity, specificity, positive predictive value, and negative predictive value. Sensitivity varied from 85 to 98%, specificity from 84 to 96%, positive predictive value from 83 to 97%, and negative predictive value from 84 to 97%. Following multivariate analysis, an evaluation of demographic and clinical factors indicated that the highest predictive accuracy was obtained from proband reporting of their children [odds ratio (OR), 0.38; 95% confidence interval (CI), 0.15 to 0.94] whereas the most inaccurate reporting of a proband was when there was less-severe maternal myopia (per 0.50 D less myopic) (OR, 1.23; 95% CI, 1.06 to 1.43) or for increase in total education of the proband (per 1 year increase) (OR, 1.22; 95% CI, 1.04 to 1.42).

CONCLUSIONS

Several variables influence the accuracy of obtaining a family history of myopia. A questionnaire-based approach alone will introduce some error into the study and this should be taken into account when designing and undertaking family-based epidemiological or genetic studies of myopia.

Apolipoprotein (APOE) gene is associated with progression of age-related macular degeneration (AMD)

Progression of age-related macular degeneration (AMD), the leading cause of blindness in the elderly, was followed in a cohort of 238 individuals from a single center. Individuals with an epsilon (epsilon)2 genotype (c.526C>T of reference sequence NM_000041.2) of the apolipoprotein (APOE) gene were found to be strongly associated with disease with a significant 4.8-fold increased relative risk compared to individuals with an epsilon4 genotype (c.388T>C of reference sequence NM_000041.2) (odds ratio [OR], 4.8; 95% confidence interval [CI], 1.19-19.09) and a nearly significant three-fold increased relative risk compared to individuals with an epsilon3 genotype (reference sequence NM_000041.2) (OR, 2.8; 95% CI, 0.96-19.09). This finding was present only in females who progressed with AMD, which suggests that there may be a gender-specific role in progression of AMD in individuals with an epsilon2 allele. A gender-related factor is therefore implicated either directly or indirectly in the AMD disease process.

Heritability of refractive error and ocular biometrics: the Genes in Myopia (GEM) twin study

PURPOSE

A classic twin study was undertaken to assess the contribution of genes and environment to the development of refractive errors and ocular biometrics in a twin population.

METHODS

A total of 1224 twins (345 monozygotic [MZ] and 267 dizygotic [DZ] twin pairs) aged between 18 and 88 years were examined. All twins completed a questionnaire consisting of a medical history, education, and zygosity. Objective refraction was measured in all twins, and biometric measurements were obtained using partial coherence interferometry.

RESULTS

Intrapair correlations for spherical equivalent and ocular biometrics were significantly higher in the MZ than in the DZ twin pairs (P < 0.05), when refraction was considered as a continuous variable. A significant gender difference in the variation of spherical equivalent and ocular biometrics was found (P < 0.05). A genetic model specifying an additive, dominant, and unique environmental factor that was sex limited was the best fit for all measured variables. Heritability of spherical equivalents of 88% and 75% were found in the men and women, respectively, whereas, that of axial length was 94% and 92%, respectively. Additive genetic effects accounted for a greater proportion of the variance in spherical equivalent, whereas the variance in ocular biometrics, particularly axial length was explained mostly by dominant genetic effects.

CONCLUSIONS

Genetic factors, both additive and dominant, play a significant role in refractive error (myopia and hypermetropia) as well as in ocular biometrics, particularly axial length. The sex limitation ADE model (additive genetic, nonadditive genetic, and environmental components) provided the best-fit genetic model for all parameters.

Analysis of the Y402H variant of the complement factor H gene in age-related macular degeneration

PURPOSE

Recent studies in U.S. populations have indicated that the Y402H variant of the complement factor H (CFH) gene contains a major risk susceptibility allele for age-related macular degeneration (AMD). This study was conducted to ascertain whether this is also true in a non-U.S. population and also whether the at-risk allele is associated with the clinical phenotype of disease and the age at diagnosis.

METHODS

Two hundred thirty-six unrelated individuals with AMD and 144 unrelated but ethnically matched control subjects were recruited and examined. All subjects completed a standard questionnaire, were given a fundus examination, and provided a blood sample for DNA extraction. Alleles of Y402H in the CFH gene were determined by use of a MALDI-TOF-based approach followed by statistical analysis.

RESULTS

Individuals with AMD who had at least one copy of the C allele of Y402H had an increased risk of disease (odds ratio [OR] 2.98; 95% confidence interval [CI] 1.81-4.93) compared with cases with the T allele. On subgroup analysis, this risk was found to be most significant in individuals with neovascular disease (OR 4.34; 95% CI 1.94, 9.71). In addition, individuals with neovascular disease who were homozygous CC presented with a significant 7.0-year earlier age at diagnosis relative to those individuals who were homozygous TT. The population-attributable risk for the C allele ranged between 47% to 69%, depending on the AMD disease subtype.

CONCLUSIONS

The C allele of Y402H represents a significant risk factor in individuals with AMD, and this effect is most pronounced in individuals with neovascular disease.

Refractive errors in twin studies

It is estimated that 1.6 billion people worldwide have myopia, a refractive error, and this number is expected to increase to approximately 2.5 billion by the year 2020. It is now well established that both the environment and genetics play a role in the development of myopia. However, the exact contribution of each of these components to myopia development has yet to be completely determined. Twin studies (classical twin model) are commonly used to determine the weighting of genetic and environmental components in disease. Over the last century, twin studies have investigated the heritability of refractive errors in different sample populations and have collectively supported a genetic basis to refractive errors. However, different sample populations and methods of data collection have produced a wide range of heritability estimates ranging from .5 to .9. This article will review those twin studies that have investigated refractive error, particularly myopia, as well as biometric measures linked to refractive error, to compare heritability estimates and methodology designs.

Concordant bilateral Duane's Retraction Syndrome (type 1) in female monozygotic twins

We report a single case study of concordant bilateral Duane's Retraction Syndrome (DRS) (type 1) in female monozygotic (MZ) twins aged 47 years. The twin pair were recruited through the Australian Twin Registry as part of a twin study on myopia. This twin pair were full term and had a similar birth weight: 2.27 kg and 1.81 kg in twin 1 and twin 2, respectively. There was no report of any other childhood medical conditions in either twin. Both twins had an equal amount of restriction in right and left abduction. Narrowing of the palpebral fissures and globe retraction in right and left adduction was also observed in both twins. To our knowledge this is the first case to report concordant bilateral DRS (type 1) in female MZ twins. The concordance for the presence of DRS and associated clinical signs observed in this MZ twin pair supports a genetic origin to DRS.

Blood storage at 4°C—factors involved in DNA yield and quality

BACKGROUND

Whole blood provides one of the most common sources of both high-quality DNA and high-quantity DNA for molecular biological purposes. Typically, blood storage at 4 degrees C is short term, which ranges from a few days to a few weeks. However, long-term storage usually involves blood being frozen, with a resultant loss in DNA yield. The authors examined the effects of long-term storage at 4 degrees C.

METHODS

Duplicate blood samples were collected from 301 participants (aged 20-98 years) enrolled as part of ongoing studies. Samples were stored at 4 degrees C for between 11 days and 922 days, and DNA was subsequently extracted using a phenol/chloroform procedure.

RESULTS

A negative correlation of the number of storage days existed at 4 degrees C with DNA yield. The main determinant on DNA yield was the age of the participant in the study, with older persons having a lower DNA yield.

CONCLUSIONS

Long-term storage of blood at 4 degrees C does have a detrimental effect on DNA yield, but this effect seemed less significant than the age of a person. The impact of age of a person or storage time has a minimal impact on DNA quality. Therefore, storage of blood at 4 degrees C offers an acceptable alternative to frozen storage.

Mirror-image congenital esotropia in monozygotic twins

Monozygotic twins had mirror-image congenital esotropia and discordant refractive errors. One had right congenital esotropia surgically corrected during childhood, and the other had left congenital esotropia surgically corrected at 3 and 6 years old.

Marked discordance for myopia in female monozygotic twins

Female monozygotic twins aged 54 years discordant for myopia are reported. One twin presented with bilateral high myopia (right eye = -6.00/+0.50 x 5 degrees , left eye = -6.00/+0.50 x 45 degrees ) and her identical twin had no significant refractive error (right eye = -0.50/plano, left eye = -0.50/+0.75 x 40 degrees ). An explanation for the striking refractive discordance seen in this case report is yet to be determined.

Heritability of Macular Thickness Determined by Optical Coherence Tomography

PURPOSE

To examine whether genetic factors significantly influence macular thickness in healthy older subjects.

METHODS

A classic twin study was performed to compare the correlation of macular thickness between monozygotic (MZ) and dizygotic (DZ) twins in a sample of population-based volunteer twins. The study included 109 white twin pairs from 50 to 80 years of age without evidence of manifest eye disease and corrected visual acuity better than 6/7.5. Dilated macular optical coherence tomography (OCT), fundus photography, clinical examination, ocular biometry, a health-dietary questionnaire, and subjective autorefraction were performed on all subjects.

RESULTS

Correlation of retinal thickness was significantly greater between MZ twin pairs than DZ pairs in all macular regions. The MZ-to-DZ correlation was 0.88:0.44 for the foveal region, 0.79:0.47 for the inner macular region, and 0.81:0.50 for the outer macular region. With adjustment for significant covariates and model fitting, final heritability estimates of 85%, 81%, and 81%, respectively, were obtained. A significant correlation between foveal thickness and gender was present, with the men having significantly thicker foveae. There was a significant negative correlation between outer macular thickness and axial length.

CONCLUSIONS

This study confirms that macular thickness in older healthy subjects, as measured by OCT, may be affected by genetic factors. Factors such as axial length, gender and age, warrant further examination in larger population-based studies, as variables that may influence macular thickness. This finding suggests an inherited basis of macular thickness and may help in the understanding of the factors that govern macular structure and function.

Linkage to 10q22 for maximum intraocular pressure and 1p32 for maximum cup-to-disc ratio in an extended primary open-angle glaucoma pedigree

PURPOSE

The purpose of this study was to identify genetic contributions to primary open-angle glaucoma (POAG) through investigations of two quantitative components of the POAG phenotype.

METHODS

Genome-wide multipoint variance-components linkage analyses of maximum recorded intraocular pressure (IOP) and maximum vertical cup-to-disc ratio were conducted on data from a single, large Australian POAG pedigree that has been found to segregate the myocilin Q368X mutation in some individuals.

RESULTS

Multipoint linkage analysis of maximum recorded IOP produced a peak LOD score of 3.3 (P = 0.00015) near marker D10S537 on 10q22, whereas the maximum cup-to-disc ratio produced a peak LOD score of 2.3 (P = 0.00056) near markers D1S197 to D1S220 on 1p32. Inclusion of the myocilin Q368X mutation as a covariate provided evidence of an interaction between this mutation and the IOP and cup-to-disc ratio loci.

CONCLUSIONS

Significant linkage has been identified for maximum IOP and suggestive linkage for vertical cup-to-disc ratio. Identification of genes contributing to the variance of these traits will enhance understanding of the pathophysiology of POAG as a whole.

A common disease haplotype for the Q368STOP mutation of the myocilin gene in Australian and Canadian glaucoma families

PURPOSE

To ascertain whether there is a common disease haplotype for the Q368STOP mutation of the myocilin gene in Australian and Canadian families with primary open-angle glaucoma (POAG).

DESIGN

Family pedigree study.

METHODS

A disease haplotype for the Q368STOP mutation of the myocilin gene has previously been identified in 15 Tasmanian families with POAG. The four microsatellite markers that constitute this 0.14-megabase (Mb) disease haplotype were genotyped in individuals from a large French Canadian family with POAG (family CT) and two unrelated French Canadian individuals with ocular hypertension.

RESULTS

The Tasmanian Q368STOP disease haplotype was identified in affected individuals from family CT, and the same alleles were shared at the four microsatellite markers in the two unrelated French Canadian individuals.

CONCLUSION

The same disease haplotype for the Q368STOP mutation of the myocilin gene was found in both the Tasmanian and French Canadian populations, supporting the view that this mutation arose from a common Caucasian founder.

The Q368STOP myocilin mutation in a population-based cohort: the Blue Mountains Eye Study

PURPOSE

To investigate the prevalence of the Q368STOP myocilin mutation in a population-based cohort: the Blue Mountains Eye Study (BMES).

DESIGN

Population-based study.

METHODS

DNA was extracted from 2,142 individuals collected through the BMES, including 31 individuals with glaucoma. All individuals were screened for the presence of the Q368STOP mutation of myocilin. Genotyping of the microsatellite markers My5, My3, D1S2815, and D1S1619 was also undertaken.

RESULTS

None of the 31 open-angle glaucoma-positive individuals presented with the Q368STOP mutation. However, two individuals (aged 56 and 72) with no clinical signs of OAG, were identified with this mutation. Allele sharing at the four microsatellite markers defining the Q368STOP disease haplotype for OAG was found in these two individuals.

CONCLUSIONS

The Q368STOP myocilin mutation occurs at a low prevalence (0.09%) in a general, older population.

Evidence for a novel glaucoma locus at chromosome 3p21-22

Primary open-angle glaucoma (POAG) is one of the leading causes of blindness in the world. It is a clinically variable group of diseases with the majority of cases presenting as the late onset adult type. Several chromosomal loci have been implicated in disease aetiology, but causal mutations have only been identified in a small proportion of glaucoma. We have previously described a large six-generation Tasmanian family with POAG exhibiting genetic heterogeneity. In this family, approximately one third of affected individuals presented with a glutamine-368-STOP (Q368STOP) mutation in the myocilin gene. We now use a Markov Chain Monte Carlo (MCMC) method to identify a second disease region in this family on the short arm of chromosome 3. This disease locus was initially mapped to the marker D3S1298 and a subsequent minimum disease region of 9 cM between markers D3S1298 and D3S1289 was identified through additional mapping. The region did not overlap with any previously described locus for POAG. Using a multiplicative relative risk model, we identified a positive association between this region and the Q368STOP mutation of myocilin on chromosome 1 in affected individuals. These findings provide evidence of a new autosomal dominant glaucoma locus on the short arm of chromosome 3.

Analysis of optineurin (OPTN) gene mutations in subjects with and without glaucoma: the Blue Mountains Eye Study

BACKGROUND

The optineurin (OPTN) gene has been reported to possess both causal as well as risk-associated alleles for open-angle glaucoma. However, these findings have so far only been reported in family and clinic based studies. The aim of this study was to investigate the spectrum of mutations and gene variants in OPTN that might be present in people with glaucoma from a population-based study, the Blue Mountains Eye Study (BMES).

METHODS

A total of 108 subjects of Caucasian origin were identified at baseline in the BMES as having open-angle glaucoma. Blood samples were available from 27 of these, of whom 18 had high-tension glaucoma and the remaining nine had normal-tension glaucoma. Ninety-four control subjects were chosen at random from the BMES, who satisfied the criteria of not having glaucoma at baseline and were over age 70 years. The 13 coding exons (exons 4-16 inclusive) and their intron-exon boundaries of OPTN were screened by the use of single-strand conformation polymorphism. Samples exhibiting mobility shifts were di-deoxy nucleotide sequenced. The M98K polymorphism was additionally screened using the restriction enzyme Stu1 in all cases and controls in this study.

RESULTS

The M98K risk-associated alteration was identified in 2/18 (11%) subjects with high-tension glaucoma, 0/9 subjects (0%) with normal-tension glaucoma and 3/94 (3.2%) controls. However, association of this variant with disease was not significant (P = 0.2 for each phenotype) for either high-tension glaucoma or normal-tension glaucoma. A novel variant (P556P in exon 16) was found in one subject with open-angle glaucoma and a previously described variant (exon 7) was found in a further subject with open-angle glaucoma and in one control. No other OPTN variants were identified in this study cohort.

CONCLUSIONS

Cross-sectional analysis from baseline observations of the BMES suggested that the M98K risk-associated allele appeared at a higher prevalence in high-tension glaucoma compared with controls, although this finding was not statistically significant.

Association of the M55L and Q192R paraoxonase gene polymorphisms with age-related macular degeneration

PURPOSE

To investigate the reported association of the two single-nucleotide polymorphisms (SNPs) of the paraoxonase gene (PON1), Met-Leu 55 (M55L) and Gln-Arg 192 (Q192R), in individuals of Anglo-Celtic descent who have age-related macular degeneration (AMD).

DESIGN

Case-control association study.

METHODS

Sixty-two individuals with late (end-stage) AMD and 115 control subjects (without AMD) were included in this study. The M55L and Q192R SNPs were amplified by polymerase chain reaction and genotyped, and statistical analysis was undertaken.

RESULTS

No association of either SNP was detected in persons of Anglo-Celtic descent who had AMD, although there was a significant difference in SNP allele frequency between Anglo-Celtic and Japanese individuals.

CONCLUSION

The M55L and Q192R SNPs of the PON1 gene do not appear to be associated with late AMD in individuals of Anglo-Celtic descent.

Analysis of the EFEMP1 gene in individuals and families with early onset drusen

AIMS

Age-related macular degeneration (AMD) is considered a complex genetic disease, although the genetic influences are not yet fully understood. Genetic analysis is hampered by the late onset of disease and the difficulty in obtaining multigenerational families. To investigate this problem further we studied our population of early onset drusen cases. The Arg345Trp mutation on exon 10 of the EGF-containing fibulin-like extracellular matrix protein 1 (EFEMP1) gene causes two clinical phenotypes of early onset drusen (Doyne honeycomb retinal dystrophy and Malattia Leventinese), yet does not appear to be involved in other early onset drusen phenotypes or typical AMD. We wished to ascertain the involvement of the EFEMP1 gene in our population of sporadic and familial subjects presenting with early onset drusen and their affected relatives.

METHODS

Individuals presenting with drusen/end-stage maculopathy at 60 years or under were identified from retinal clinics in Melbourne. All available first- and second-degree relatives were also examined. In all, 116 ethnically matched controls were collected from the same community for comparison.

RESULTS

Single stranded conformational polymorphism (SSCP) analysis and subsequent sequencing revealed four previously described and three novel sequence variations. Most occurred at similar frequencies in the case and control populations and were not thought to be disease associated.

CONCLUSION

The term early onset drusen encompasses a wide range of phenotypes and our findings indicate that it is likely that more than one gene is involved in its causation. It is essential that these clinical phenotypes are well described and categorised to allow greater possibility of success in the search for other disease genes.

The epsilon2 and epsilon4 alleles of the apolipoprotein gene are associated with age-related macular degeneration

PURPOSE

To date, of all the genes studied in relation to age-related macular degeneration (AMD), the alleles of the apolipoprotein (apoE) gene have been the most consistently associated with disease. However, not all apoE studies have found an association, and among these the associations differ. The current study was conducted to investigate further the association of this gene in AMD.

METHODS

Three hundred twenty-two unrelated individuals with diagnosed AMD and 123 unrelated but ethnically matched control subjects were analyzed. All subjects completed a standard questionnaire and were given a fundus examination. A blood sample was collected for DNA extraction. The common allelic variants of apoE were screened through the use of polymerase chain reaction (PCR) and restriction enzyme digestion followed by statistical analysis.

RESULTS

Individuals with the epsilon3 epsilon4 genotype of apoE had an approximate halving of disease risk for late (end-stage) AMD (odds ratio [OR] 0.58, 95% confidence interval [CI] 0.34-0.98) relative to the epsilon3 epsilon3 genotype at age of ascertainment. Stratification of late AMD into atrophic and neovascular disease revealed that the greatest protective effect for the epsilon3 epsilon4 genotype was in individuals with atrophic disease (OR 0.35, 95% CI 0.13-0.92). Men with the epsilon3 epsilon4 genotype also showed almost a threefold reduction in risk of disease in late AMD (OR 0.36, 95% CI 0.16-0.82). However, individuals with late AMD and the epsilon2 epsilon3 genotype had a significantly earlier mean age of diagnosis of disease (3.4 years, P = 0.015) compared with those with the epsilon3 epsilon3 genotype, and this was most evident in women (3.9 years, P = 0.011) and in individuals with neovascular disease (4.7 years, P = 0.003).

CONCLUSIONS

The alleles of apoE appear to have a role in the etiology of AMD, with the epsilon4 allele being protective, or at the very least, delaying the age of diagnosis of disease, whereas the epsilon2 allele appears to have a modifier effect by bringing forward the mean age of disease diagnosis.

Analysis of 15 primary open-angle glaucoma families from Australia identifies a founder effect for the Q368STOP mutation of myocilin

Primary open-angle glaucoma (POAG) is a leading cause of blindness in the world. A number of mutations in the myocilin gene have been identified that predispose to glaucoma. The most frequent of these is the Glutamine368STOP (Q368STOP) mutation. It has been postulated that individuals with the Q368STOP mutation are derived from a common founder. To clarify this situation, we studied 15 unrelated POAG families who carried the Q368STOP mutation, from south eastern Australia. In one large family, nine affected and ten unaffected individuals were identified with the Q368STOP mutation. Closely linked polymorphic microsatellite markers were used to establish a disease haplotype in this family. Additional genotyping of markers in another 14 unrelated Q368STOP families revealed the presence of the same disease haplotype. These findings indicate that the Q368STOP mutation in all 15 families shared a common origin prior to the European settlement of Australia in the early 1800s.

Analysis of the Arg345Trp disease-associated allele of the EFEMP1 gene in individuals with early onset drusen or familial age-related macular degeneration

BACKGROUND

A single base change within the EFEMP1 gene has been associated with malattia leventinese and Doyne honeycomb retinal dystrophy, two dominantly inherited macular diseases with early onset drusen. The aim of this study was to determine whether the same disease allele was also associated with other forms of early onset drusen or familial cases of age-related macular degeneration.

METHODS

Thirteen index cases of early onset drusen together with 15 other family members were examined. In addition, 54 familial cases of age-related macular degeneration were examined. Blood was taken for DNA analysis and screened for the Arg345Trp disease-associated allele of the EFEMP1 gene. Twenty-four cases of malattia leventinese or Doyne honeycomb retinal dystrophy were also screened as positive controls. Another 150 ethnicity- and age-matched individuals acted as controls.

RESULTS

The Arg345Trp disease-associated allele in the EFEMP1 gene was confirmed in individuals with malattia leventinese and Doyne honeycomb retinal dystrophy. However, involvement of this allele was not evident in either early onset drusen or familial age-related macular degeneration.

CONCLUSIONS

The Arg345Trp disease-associated allele of the EFEMP1 gene does not appear to be associated with cases of early onset drusen that fall outside the diagnosis of malattia leventinese or Doyne honeycomb retinal dystrophy, nor does it appear to play a role in familial age-related macular degeneration. These findings do not exclude the involvement of other alleles of the EFEMP1 gene in either phenotype. The genetic mechanisms involved in the heterogeneous group of early onset drusen remain to be elucidated but should lead to insights into the genetic causes of macular diseases.