A twin study of cilioretinal arteries, tilted discs and situs inversus

To establish the prevalence and heritability of cilioretinal arteries (CRAs), tilted discs (TDs) and situs inversus (SI). Fundus photos from the Twins UK Adult Twin registry twin database were analyzed: 1812 individuals, 526 complete monozygotic (MZ) twin pairs and 336 complete dizygotic (DZ) pairs. Images were assessed non-stereoscopically on a computer screen by the same ophthalmologist for presence of CRAs, TDs or SI. Prevalence figures, probandwise concordances and heritabilities were calculated. Prevalence of a CRA in subjects' right eyes was 28.6% (26.5-30.8). Prevalence of subjects with a CRA in at least one eye was 45.0% (42.6-47.5), with a TD in at least one eye was 1.2% (0.8-1.9), and with SI at least one eye was 0.5% (0.3-1.0). There was no association between birth weight and presence of CRA. Concordance for CRA in at least one eye (MZ twins) was 60% (95% CI 55-64), and (DZ) was 45% (95% CI 39-51). Heritability for CRAs in at least one eye was 49.4% (95% CI 38.1-59.7) and for both eyes was 32.9% (95% CI 10.4-53.3). We were unable to calculate meaningful heritabilities or concordances for TDs and situs SI, due to insufficient numbers. The presence of CRAs appears to be moderately heritable, with greater variance explained by individual environmental factors or even stochastic events. They were not associated with low birth weight. Future genetic research and studies of birth/lifecourse cohorts may offer further insights into the etiology of congenital papillovascular abnormalities.