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Abstract
Purpose
The concordance of strabismus in monozygotic twins was examined in order to study the role of genetics in the different types of strabismus.
Methods
The medical charts of 39 pairs of monozygotic twins (63 of 78 subjects had strabismus) dated between May 1985 and December 2005 were reviewed retrospectively. We analyzed each case by refraction, type of strabismus, age of onset, amount of deviation, and stereopsis.
Results
Twenty-three of 39 pairs of twins (59%) showed phenotypic concordance; 15 of 21 pairs showed intermittent exotropia (71%), five of nine pairs showed infantile esotropia (55%), and three of four pairs showed partially accommodative esotropia (75%). All pairs with accommodative esotropia showed discordance. One discordant pair showed infantile esotropia, one expressed infantile esotropia, and another expressed sensory exotropia due to congenital cataract.
Conclusions
The concordance rate of monozygotic twins was 59% in this study. Partially accommodative esotropia and intermittent exotropia had high concordance rates of strabismic phenotypes in monozygotic twins. Based on the results of this study, it is suggested that there may be a strong genetic component regarding these types of strabismus. Concordant pairs of monozygotic twins showed similarity in onset, deviation angle, postoperative result, and recurrence
References
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Table 1.
Type of strabismus and concordance rate of strabismic type
| Type of strabismus | Concordant (pairs) | Discordant (pairs) | Concordance rate (%) |
|---|---|---|---|
| Intermittent XT∗ | 15 | 6 | 71 |
| Infantile E† | 5 | 4 | 55 |
| Partially accommodative ET† | 3 | 1 | 75 |
| Accommodative E† | 0 | 4 | 0 |
| Brown syndrome | 0 | 1 | 0 |
| Total | 23 | 16 | 59 |
Table 2.
Onset age and deviation angle in concordant pairs
| Type of strabismus | Case No |
Age of onset |
Deviation angle (PD‡) |
Difference of deviation | ||
|---|---|---|---|---|---|---|
| 1st child | 2nd child | 1st child | 2nd child | |||
| Intermittent XT∗ | 1 | 7 yr | 7 yr | 56 | 54 | 2 |
| 2 | 2 yr | 2 yr | 35 | 30 | 5 | |
| 3 | 2 yr | 2 yr | 25 | 25 | 0 | |
| 4 | 1 yr | 1 yr | 20 | 20 | 0 | |
| 5 | 1 yr | 10 yr | 20 | 16 | 4 | |
| 6 | 1 yr | 1 yr | 30 | 30 | 0 | |
| 7 | 1 yr | 2 yr | 25 | 20 | 5 | |
| 8 | 1 yr | 1 yr | 15 | 10 | 5 | |
| 9 | 2 yr | 2 yr | 25 | 25 | 0 | |
| 10 | 2 yr | 2 yr | 25 | 30 | 5 | |
| 11 | 2 yr | 1 yr | 35 | 35 | 0 | |
| 12 | 5 yr | 5 yr | 20 | 20 | 0 | |
| 13 | 1 yr | 1 yr | 25 | 25 | 0 | |
| 14 | 6 yr | 6 yr | 22 | 20 | 2 | |
| 15 | 7 yr | 7 yr | 22 | 22 | 0 | |
| Infantile ET† | 1 | 2 mo | 2 mo | 70 | 70 | 0 |
| 2 | 3 mo | 3 mo | 30 | 30 | 0 | |
| 3 | < 3 mo | < 3 mo | 20 | 25 | 5 | |
| 4 | < 3 mo | < 3 mo | 15 | 8 | 7 | |
| 5 | < 3 mo | < 3 mo | 70 | 55 | 15 | |
| Partially accommodative ET† | 1 | 1 yr | 1 yr | 15 | 35 | 20 |
| 2 | 15 mo | 1 yr | 40 | 32 | 8 | |
| 3 | 3 yr | 3 yr | 10 | 30 | 20 | |
Table 3.
Postoperative deviation angle in concordant twins
| Type of strabismus | Case No |
Postoperative deviation angle (PD‡) |
Reoperative deviation angle (PD‡) |
||
|---|---|---|---|---|---|
| 1st child | 2nd child | 1st child | 2nd child | ||
| Intermittent XT∗ | 1 | 0 | 0 | ||
| 2 | 2 | 0 | |||
| 3 | 20 | 25 | 16 | 20 | |
| 4 | 0 | 0 | |||
| 5 | 18 | no op | |||
| 6 | 20 | 20 | 4 | 10 | |
| 7 | 0 | 6 | |||
| 8 | 15 | 10 | 0 | 2 | |
| 9 | 14 | 12 | |||
| 10 | 0 | 4 | |||
| 11 | 0 | 5 | |||
| 12 | 2 | 0 | |||
| 13 | 12 | 10 | |||
| Infantile ET† | 1 | 0 | 0 | ||
| 2 | 0 | 0 | |||
| 3 | 0 | no op | |||
| 4 | 25 | 8 | |||
| Partially accommodative ET† | 1 | 0 | 12 | no op | 5 |
| 2 | 4 | 5 | |||
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