Heritability of the spatial distribution and peak density of macular pigment: a classical twin study

Abstract

Purpose: To elucidate the heritability of peak density and spatial width of macular pigment (MP) using a Classical Twin Study.

Methods: Fundus autofluorescence images were obtained at 488 nm from 86 subjects or 43 twin pairs (21 monozygotic (MZ) and 22 dizygotic (DZ)) (27 male, 59 female) aged from 55 to 76 years (mean 62.2 ± 5.3 years). The relative topographic distribution of MP was measured using a grey scale of intensity (0-255 units) in a 7° eccentricity around the fovea. Relative peak MP density (rPMPD) and relative spatial distribution of MP (rSDMP) were used as the main outcome measure in the statistical analysis.

Results: A significantly higher correlation was found within MZ pairs as compared with that within DZ pairs for rPMPD, (r=0.99, 95% confidence interval (95% CI) 0.93 to 1.00) and 0.22, 95% CI -0.34 to 0.71), respectively, suggesting strong heritability of this trait. When rSDMP was compared, there was no significant difference between the correlations within MZ pairs (r=0.48, 95% CI -0.02 to 0.83) and DZ pairs (r=0.63, 95% CI 0.32 to 0.83), thus rSDMP is unlikely to have a considerable heritable component. In addition, there was no difference between any MP parameter when normal maculae were compared with early age-related macular degeneration (AMD) (rPMPD 0.36 vs 0.34, t=1.18 P=0.243, rSDMP 1.75 vs 1.75, t=0.028 P=0.977).

Conclusions: rPMPD is a strongly heritable trait whereas rSDMP has minimal genetic influence and a greater influence by environmental factors. The presence of macular changes associated with early AMD did not appear to influence any of these pigment parameters.

Figure 1

MP density measured in a 7° radius from the centre of the fovea.

Figure 2

Graph of MP spectral profile (horizontal) explaining ‘a' (rPMPD) and ‘b' (rSDMP) values.

Figure 3

Typical MP spectral profiles for MZ (left) and DZ (right) twins. A closer correlation is observed in the profiles of MZ twins than DZ twins. Twin 1 upper, twin 2 lower.

Figure 4

Graphs showing the correlation for rPMPD density between MZ twin pairs (a) and DZ twin pairs (b) and the correlation for the relative rSDMP between MZ twin pairs (c) and DZ twin pairs (d).