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To examine the familial correlations, heritability ( h 2) and common environmental components ( c 2) of myopia and ocular biometric traits (all treated as continuous outcomes) in families collected through the Genes in Myopia (GEM) family study in Australia. A total of 132 pedigrees (723 participants) were recruited for this study. All individuals completed a risk factor questionnaire and underwent a detailed eye examination including spherical equivalent (SphE) and ocular biometric measurements of axial length (AL), anterior chamber depth (ACD) and corneal curvature (CC). Familial correlations were calculated and h 2 and c2 were estimated using a variance component model that assumes a multivariate t distribution within each pedigree. Two definitions of common environments ( c 2) were considered: nuclear family (current) shared environment (Model 1) and sib-ship (childhood) shared environment (Model 2). Population ascertainment adjustment was performed using the Blue Mountains eye study dataset. The trends observed for familial correlations suggested that SphE is influenced by both environmental and genetic factors whereas AL, ACD and CC are predominantly genetically determined. This was largely confirmed by variance components modelling. Heritability estimates (adjusted for age, sex and years of education) from the best fitting ACE model (Model 2, childhood shared environment) were 0.50 ± 0.05 for SphE, 0.73 ± 0.04 for AL, 0.78 ± 0.04 for ACD and 0.16 ± 0.06 for CC. Childhood environmental effects were significant with c 2 estimated to be 0.33 ± 0.04 for SphE, 0.06 ± 0.03 for AL, 0.22 ± 0.04 for ACD and 0.10 ± 0.05 for CC. Age was associated with SphE, total years of education was associated with AL and sex was associated with all traits studied. We used a novel and conservative approach to account for and estimate common environmental effects by specifying either nuclear family or sib-ship environment when estimating heritability estimates and showed that all traits examined (SphE, AL, ACD and CC) are heritable, thus reflecting a genetic component. These traits therefore all represent candidates for quantitative trait linkage analyses. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Purpose: Myopia is considered to be a complex disease involving both environmental and genetic factors. The Genes in Myopia (GEM) Study aims to recruit probands with myopia and their family members to allow genetic analysis of myopia to be undertaken. The purpose of this paper is to describe the methodology and recruitment of probands and families for the GEM Study., Methods: In a sample-based prospective study, 2,095 probands with myopia of -0.50 DS or worse and a positive family history of myopia were contacted via the Melbourne Excimer Laser Group (MELG) database. Probands and family members recruited into the study undertook a detailed assessment including questionnaire, best-corrected visual acuity, objective and subjective refraction, axial length, anterior chamber depth, keratometry readings, slit-lamp examination, height, weight and head circumference measurements, and blood sample collection for DNA analysis., Results: 280 probands with myopia have been recruited into the GEM Study. Probands had a mean age of 49.33 yrs. (SD +/- 11.64) with the average age of myopia onset being 12.58 years (SD +/- 6.71). The average spherical-component refractive error was: right eye -5.13 DS (SD +/- 3.06) and left eye -5.14 DS (SD +/- 3.16). Probands with extreme myopia (-10 DS or worse) showed the highest study participation rate of 56%, when compared to high (-5 DS < -10 DS) (20%), moderate (-3 DS < - 5 DS) (18%) and low myopia (-0.5 DS < -3 DS) (10%). A total of 279 out of 505 (55%) additional family members recruited were also found to be myopic., Conclusions: The GEM study has used a targeted approach to identify an Australian cohort with a diverse spread of myopia, ranging from low to extreme. Recruitment of probands via the use of an excimer laser practice has proved to be an efficient and economic means of identifying probands with a family history of myopia. In addition, the participation rate in the study appears to vary reflecting a proband's perception of disease severity.