The genetics of keratoconus

Keratoconus is a relatively common, bilateral, noninflammatory corneal ectasia. The aetiology of this condition is probably multifactorial, or it represents the final common pathway for a variety of different pathological processes. Although a familial history is present only in a minority of cases, one of the major aetiological factors is certainly genetic. This is evidenced by: the condition's familial inheritance; its discordance between monozygotic and dizygotic twins; and its association with other known genetic disorders such as Down's and Marfan's syndromes. In the keratoconic cornea, a possible genetic predisposition to increased sensitivity to apoptotic mediators by keratocytes has also been hypothesized. Differences in prevalence between ethnic groups have been identified. Recent advances in computerized topographic diagnostic techniques for keratoconus, including forme fruste keratoconus, enables higher accuracy in delineating abnormal from normal, and helps define study populations for genetic linkage studies. However, genetic heterogeneity and the phenotypic diversity of keratoconus means that genetic analysis continues to be a complex process. None the less, it is foreseeable that over the next decade, improved diagnostic techniques, in combination with molecular genetics, may reveal conclusive data on the precise nature of the genetic inheritance of keratoconus in specific populations. This review considers the evidence that suggests keratoconus is primarily an inherited condition, and examines research strategies aimed at unveiling the genetic predisposition, and the enigma of environmental influences on its phenotypic expression.