Keratoconus in 18 pairs of twins.
OBJECTIVE
To describe the concordance of keratoconus in 18 sets of twins.


METHODS
Thirteen monozygotic (MZ) and five dizygotic (DZ) pairs of twins were identified during an investigation of familial keratoconus. We used 16 forensic microsatellite markers to confirm the zygosity of same sex twins. Patients and available relatives were examined for signs of keratoconus using corneal topography. For each pair of twins, the severity of keratoconus in each eye was graded according to the steepest keratometry value and the average difference in score between the MZ and DZ twins compared.


RESULTS
All of the MZ twins and four of the five DZ twins were concordant for keratoconus but with differences in age of onset and severity of disease. The subjective age of onset of keratoconus tended to be earlier in the MZ twins (16.4 years, SD 4.66) than in the DZ twins (20.3 years, SD 7.55) (p=0.086). Additional relatives with keratoconus were identified in two (16%) of the families with MZ twins and in three (60%) of the families of DZ twins. The mean difference in severity scores was 1.4 (SD 1.73) for the MZ twins and 3.0 (SD 1.00) for the DZ twins (p=0.035).


CONCLUSIONS
This data provide evidence that the severity of keratoconus is more concordant in MZ than in DZ twins. The results support the currently accepted hypothesis of an important genetic contribution towards the pathogenesis of keratoconus, but suggest that there is also an environmental effect on the expression of disease.
Moorfields Eye Hospital NHS Foundation Trust, London, UK.
Stephen J
SJ
Tuft
Hala
H
Hassan
Sonia
S
George
David G
DG
Frazer
Colin E
CE
Willoughby
Petra
P
Liskova
D000293:Adolescent; D000328:Adult; D002648:Child; D019781:Corneal Topography; D004200:Diseases in Twins / Q000235:genetics*; D005260:Female; D005819:Genetic Markers; D005838:Genotype; D060005:Genotyping Techniques; D006801:Humans; D007640:Keratoconus / Q000175:diagnosis / Q000235:genetics*; D008297:Male; D018895:Microsatellite Repeats; D010641:Phenotype; D014429:Twins, Dizygotic / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*; D055815:Young Adult
D005819:Genetic Markers