The heritability of the ring-like distribution of macular pigment assessed in a twin study

Macular and Plasma Xanthophylls Are Higher in Age-related Macular Degeneration than in Normal Aging: Alabama Study on Early Age-related Macular Degeneration 2 Baseline

Purpose

Quantification of retinal xanthophyll carotenoids in eyes with and without age-related macular degeneration (AMD) via macular pigment optical volume (MPOV), a metric for xanthophyll abundance from dual wavelength autofluorescence, plus correlations to plasma levels, could clarify the role of lutein (L) and zeaxanthin (Z) in health, AMD progression, and supplementation strategies.

Design

Cross-sectional observational study (NCT04112667).

Participants

Adults ≥ 60 years from a comprehensive ophthalmology clinic, with healthy maculas or maculas meeting fundus criteria for early or intermediate AMD.

Methods

Macular health and supplement use was assessed by the Age-related Eye Disease Study (AREDS) 9-step scale and self-report, respectively. Macular pigment optical volume was measured from dual wavelength autofluorescence emissions (Spectralis, Heidelberg Engineering). Non-fasting blood draws were assayed for L and Z using high-performance liquid chromatography. Associations among plasma xanthophylls and MPOV were assessed adjusting for age.

Main Outcome Measures

Age-related macular degeneration presence and severity, MPOV in fovea-centered regions of radius 2.0° and 9.0°; plasma L and Z (μM/ml).

Results

Of 809 eyes from 434 persons (89% aged 60-79, 61% female), 53.3% eyes were normal, 28.2% early AMD, and 18.5% intermediate AMD. Macular pigment optical volume 2° and 9° were similar in phakic and pseudophakic eyes, which were combined for analysis. Macular pigment optical volume 2° and 9° and plasma L and Z were higher in early AMD than normal and higher still in intermediate AMD (P < 0.0001). For all participants, higher plasma L was correlated with higher MPOV 2° (Spearman correlation coefficient [Rs] = 0.49; P < 0.0001). These correlations were significant (P < 0.0001) but lower in normal (Rs = 0.37) than early and intermediate AMD (Rs = 0.52 and 0.51, respectively). Results were similar for MPOV 9°. Plasma Z, MPOV 2°, and MPOV 9° followed this same pattern of associations. Associations were not affected by supplement use or smoking status.

Conclusions

A moderate positive correlation of MPOV with plasma L and Z comports with regulated xanthophyll bioavailability and a hypothesized role for xanthophyll transfer in soft drusen biology. An assumption that xanthophylls are low in AMD retina underlies supplementation strategies to reduce progression risk, which our data do not support. Whether higher xanthophyll levels in AMD are due to supplement use cannot be determined in this study.

Twins' Macular Pigment Optical Density Assessment and Relation with SCARB1 Gene Polymorphism

THE AIM OF THE STUDY

to assess the influence of genetic and environmental factors using twin studies and evaluate the associations of SCARB1 gene variants (rs11057841) with AMD and MPOD.

MATERIAL AND METHODS

a total of 108 healthy twins (56 MZ and 52 DZ twins) were tested in this study. The MPOD was measured using the one-wavelength reflectometry method. Fundus reflectance (Visucam 500, reflectance of a single 460 nm wavelength) was used to measure the MPOD levels, MPOD parameters including max and mean optical density (OD), and area and volume. Real-time polymerase chain reaction was used to detect single nucleotide polymorphisms.

RESULTS

we detected a positive correlation of MPOD in the right and left eyes in MZ twin pairs (r = 0.830 and r = 0.860, respectively) (p < 0.0001) and a negative correlation of MPOD in the right and left eyes in DZ twin pairs (r = 0.314 and r = 0.408, respectively) (p < 0.05). The study was able to identify statistically significant differences in mean MPOD values in the right and left eyes between subjects with a wild-type CC genotype and a CT genotype with a risk allele. A decrease in the mean MPOD value was observed in group II with a CT genotype (0.110 d.u.) compared with the CC genotype (0.117 d.u.) in the right eye (p = 0.037) and in the left eye with a CT genotype (0.109 d.u.) compared with a CC genotype in the subjects (0.114 d.u.) (p = 0.038). In the right eye, in group II (0.101-0.128 d.u.), those with a CT genotype (n = 6) with one risk allele had a statistically significantly lower (0.110 d.u.) mean average MPOD value compared with those with a wild-type CC genotype (n = 25) (0.117 d.u.) (p = 0.037).

CONCLUSION

this twin study showed a strong heritability of the retina pigment, which was 86% prevalent in Lithuania. Individuals with a CT genotype of the SCARB1 rs11057841 with a risk allele had statistically significantly lower mean MPOD values in both eyes compared to subjects with a wild-type CC genotype.

From carotenoid intake to carotenoid blood and tissue concentrations - implications for dietary intake recommendations

There is uncertainty regarding carotenoid intake recommendations, because positive and negative health effects have been found or are correlated with carotenoid intake and tissue levels (including blood, adipose tissue, and the macula), depending on the type of study (epidemiological vs intervention), the dose (physiological vs supraphysiological) and the matrix (foods vs supplements, isolated or used in combination). All these factors, combined with interindividual response variations (eg, depending on age, sex, disease state, genetic makeup), make the relationship between carotenoid intake and their blood/tissue concentrations often unclear and highly variable. Although blood total carotenoid concentrations <1000 nmol/L have been related to increased chronic disease risk, no dietary reference intakes (DRIs) exist. Although high total plasma/serum carotenoid concentrations of up to 7500 nmol/L are achievable after supplementation, a plateauing effect for higher doses and prolonged intake is apparent. In this review and position paper, the current knowledge on carotenoids in serum/plasma and tissues and their relationship to dietary intake and health status is summarized with the aim of proposing suggestions for a "normal," safe, and desirable range of concentrations that presumably are beneficial for health. Existing recommendations are likewise evaluated and practical dietary suggestions are included.

Segmented Macular Layer Volumes from Spectral Domain Optical Coherence Tomography in 184 Adult Twins: Associations With Age and Heritability

Purpose

To investigate segmented macular layer volumes from a healthy adult twin cohort (TwinsUK), exploring changes with age and heritability.

Methods

Macular spectral domain optical coherence tomography images were acquired from monozygotic (MZ) and dizygotic (DZ) twins in a cross-sectional study. The following layer volumes were derived for circles of 3 and 6 mm diameter around the foveal center, using automated segmentation software: retinal nerve fiber layer (RNFL), ganglion cell–inner plexiform layer (GCIPL), inner nuclear layer (INL), outer plexiform layer (OPL), outer nuclear layer (ONL), photoreceptors (PR), retinal pigment epithelium (RPE), and total retinal volume (TRV). Correlation coefficients (intereye; age; intrapair for MZ and DZ pairs) were quantified; heritability was estimated using structural equation modeling.

Results

Scans from 184 participants were included. Intereye correlation was highest for TRV and GCIPL. Negative correlations with age (for 3- or 6-mm areas, or both) were observed for TRV, RNFL, GCIPL, and INL. Positive correlations were observed for PR, RPE, and OPL. For all layers, intrapair correlation was greater for MZ than DZ pairs. Heritability estimates were highest (>80%) for TRV and GCIPL volume, and lowest for RPE volume.

Conclusions

Although TRV was negatively correlated with age, all layers did not show negative correlation. Some inner layers thinned with age, whereas some outer volumes increased (not the ONL). Reduced RPE phagocytic function with age and remodeling in the OPL could be contributing factors. Heritability estimates were highest for inner retinal layers (particularly GCIPL), and lowest for RPE volume.

Repeatability of the macular pigment spatial profile: A comparison of objective versus subjective classification

PURPOSE

Classification of macular pigment (MP) spatial profile phenotypes varies and is often based on subjective visualisation. We investigated repeatability of MP optical density (MPOD) comparing an objective versus subjective profiling system.

METHODS

The coefficient of repeatability (CoR) was calculated for point MPOD values (0-3.8°) obtained by dual-wavelength fundus autofluorescence (FAF) from two scans obtained in a single visit of 40 healthy individuals (39 ± 9 years). For each individual's dataset, the MP profile was classified as exponential, ring-like or central dip using an objective method (based on deviations away from an exponential fit), as well as by subjective visual profiling. Existing FAF images of 88 monozygotic (MZ) and 69 dizygotic (DZ) twin pairs were reanalysed using the objective profiling method and concordance and heritability of ring-like profiles determined.

RESULTS

The CoR was 0.23 at 0° and 0.06 at 0.8°. Agreement of objective profiling between scans was excellent (κ = 0.85, 95% CI 0.69 to 1.00; p < 0.0005). Subjective profiling showed moderate agreement between scans (κ = 0.48, 95% CI 0.23 to 0.73; p < 0.0005). Agreement between objective and subjective classification was low (κ = 0.23, 95% CI 0.04 to 0.42; p = 0.02). Concordance for the ring-like profile using objective profiling was 0.74 for MZ compared to 0.36 for DZ twins. Heritability was calculated as 81.5% (95% confidence interval 61.1-93.1%).

CONCLUSION

Compared to visual assessment, objective MP profiling is a more reliable method and should be considered in future observational and interventional studies. In addition, MP profile phenotypes showed high heritability.

Relative Genetic and Environmental Contributions to Variations in Human Retinal Electrical Responses Quantified in a Twin Study

Purpose

To estimate heritability of parameters of human retinal electrophysiology and to explore which parameters change with age.

Design

Prospective, classic twin study.

Participants

Adult monozygotic and dizygotic twin pairs recruited from the TwinsUK cohort.

Methods

Electroretinogram responses were recorded using conductive fiber electrodes in response to stimuli incorporating standards set by the International Society for the Clinical Electrophysiology of Vision. These parameters were extracted; in addition, photopic negative-response (PhNR; originating from retinal ganglion cells) and i-wave components were extracted from responses to the photopic single flash. Parameter values were averaged from both eyes.

Main Outcome Measures

Mean values were calculated for the cohort. Correlation coefficients with age were calculated (averaging parameters from both twins from each pair). Coefficients of intrapair correlation were calculated for monozygotic and dizygotic twins. Age-adjusted heritability estimates were derived using standard maximum likelihood structural equation twin modeling.

Results

Responses were recorded from 210 participants in total (59 monozygotic and 46 dizygotic twin pairs). Ninety-three percent were women. Mean age for the cohort was 62.4 years (standard deviation, 11.4 years). In general, response amplitudes correlated negatively, and implicit times positively, with age. Correlations were statistically significant (P < 0.05) and moderate or strong (coefficient, >0.35) for the following parameters: scotopic standard and bright-flash a-wave implicit times, photopic 30-Hz flicker and single-flash b-wave implicit times, and PhNR and i-wave implicit times. Intrapair correlations were higher for monozygotic than dizygotic twins, suggesting important genetic influences. Age-adjusted estimates of heritability were significant for all parameters (except scotopic dim-flash b-wave implicit time), ranging from 0.34 to 0.85. Highest estimates were for photopic single-flash a-wave and b-wave amplitudes (0.84 and 0.85, respectively).

Conclusions

This study explored heritability of retinal electrophysiologic parameters and included measurements reflecting ganglion cell function. Most parameters showed significant heritability, indicating that genetic factors are important, determining up to 85% of the variance in some cone system response parameters. Scotopic responses tended to show lower heritability (possibly relating to greater rod system susceptibility to environmental factors). Future studies can explore the identity of these genetic factors, improving our understanding of how they shape retinal function.

Changes of macular pigment optical density in elderly eyes: a longitudinal analysis from the MARS study

Background

Macular pigment (MP) has been related to the occurrence of age related macular degeneration (AMD). We investigated prospectively in eyes of elderly individuals how magnitude and spatial distribution of MP had changed after 4 years.

Methods

The study included 380 eyes from 237 participants of the Münster Ageing and Retina Study cohort which were free of advanced stages of AMD. MP optical density (MPOD) was measured in density units (D.U.) at eccentricities of 0.25°, 0.5°, 1.0° and 2.0° from the fovea using dual-wavelength autofluorescence; ring-like MP distributions were identified from MP density profiles. Changes were assessed with mixed linear models.

Results

The study participants’ mean age at baseline was 70.5 years. Early AMD was present in 150 study eyes (39.5 %) and a ring-like distribution of MPOD was found in 87 study eyes (22.9 %). After a median follow-up time of 3.96 years, the MPOD averaged over all eyes was slightly raised at the central fovea (from 0.658 to 0.670 D.U. (relative change +1.8 %), p = 0.08) and most markedly at 2.0° (from 0.157 to 0.172 D.U. (+9.5 %), p < 0.001). Multivariate analyses, adjusting for sex, body mass and carotenoid supplement intake, revealed that MPOD increments, at any distance from the fovea, were slightly less pronounced in older eyes. Serum concentrations of lutein at follow-up, presumably reflecting recent intake of antioxidant supplements, raised MPOD levels significantly at 1.0° and 2.0° (both p < 0.01) but not in the central fovea. Early AMD at baseline and ring-like MPOD distribution did not significantly impact on MPOD changes over time. A ring-like spatial distribution of MPOD persisted in over 80 % of the affected eyes.

Conclusions

Overall, the magnitude and spatial arrangement of MPOD was remarkably stable over time in elderly eyes. Significant MPOD rises in perifoveal regions probably indicate effects of lutein containing supplements. The persistence of ring-like MPOD distributions over time seems to suggest their determination by anatomical structures.

Electronic supplementary material

The online version of this article (doi:10.1186/s40942-016-0039-6) contains supplementary material, which is available to authorized users.