Discordant Keratoconus in Monozygotic Twins

Abstract

We report a case of discordant keratoconus (KC) in a set of monozygotic twins with contrasting environmental risk factors. Twin one had bilateral, asymmetrical KC. He reported significant eye rubbing using his knuckles during his night-shift work as an emergency doctor. His usual sleeping position on the left side corresponded to the most affected eye. Twin two had normal corneas, with no evidence of KC. He reported mild infrequent eye rubbing, daytime work pattern, and a supine sleeping position. This case report highlights the influence of environmental and behavioural factors in the development of KC, in particular eye rubbing, night work, and sleeping position, in two individuals sharing identical genetic inheritance.

Letter Regarding: Socioeconomic Correlates of Keratoconus Severity and Progression

“…[2][3][4] Both genetic susceptibility and environmental factors (namely, eye rubbing or nocturnal ocular compression related to sleep position) have been suggested to play an important role. [3][4][5][6][7][8][9] Unfortunately, neither of these 2 variables were included in the analysis by Ahmad et al because of the absence of related information within the medical records. We consider this an important confounding factor in reaching definitive conclusions from the aforementioned study, and the possibility of spurious associations cannot be ruled out.…”

“…2–4 Both genetic susceptibility and environmental factors (namely, eye rubbing or nocturnal ocular compression related to sleep position) have been suggested to play an important role. 3–9…”

AvaGen Genetic Testing versus Ocular Screening Assessments Including the Keratoconus Severity Score (KSS) and Randleman Ectasia Risk Score System (ERSS) in Refractive Surgery Candidates

“…13,14 While the etiology of KC remains unclear, numerous studies have indicated a genetic predisposition, with a positive family history observed in 6-8% and up to 25% of KC patients 1 and a higher concordance rate in monozygotic twins. [15][16][17] Despite these genetic associations, ongoing scientific discourse is fueled by findings such as the notable disparity among KC in some monozygotic twins, 18 the plausible mechanisms associating recurrent corneal trauma secondary to eye rub and nighttime ocular compression and KC, 1 the absence of corneal ectasia in Marfan syndrome, 1 and several reported cases of entirely unilateral KC related to unilateral eye rubbing. 1,19 This debate on the relative importance of genetic versus environmental factors in KC continues as new insights and complexities emerge.…”