Associations between siblings for esotropia and exotropia
M. J. Podgor, N. A. Remaley and E. Chew
Division of Biometry and Epidemiology, National Eye Institute, National Institutes of Health, Bethesda, Md, USA.
OBJECTIVE: To quantify familial aggregation of esotropia and exotropia in
children examined in a large multicenter study. METHODS: Pregnant women and
their children were examined in the Collaborative Perinatal Project of the
National Institute of Neurological Disorders and Stroke, Bethesda, Md.
Strabismus was evaluated in the children during follow-up examinations up
to the age of 7 years. The second-order generalized estimating equations
approach to logistic regression was used to estimate familial aggregation
of esotropia and exotropia. RESULTS: For any pair of siblings, the odds for
one sibling having esotropia more than doubled when the other sibling had
esotropia. For exotropia, there were differences in sibling associations
based on birth relationships. In particular, there was no statistically
significant association between siblings from separate single births. On
the other hand, for the pairs of siblings from multiple births (ie, twins,
triplets, and quadruplets), the odds for exotropia in one sibling were
increased by at least a factor of 17 when the other sibling from that birth
also had exotropia. For both esotropia and exotropia, adjustment for
previously identified risk factors only somewhat reduced the magnitudes of
the observed associations. Limited data on zygosity showed a stronger
association between monozygotic twins than between dizygotic twins.
CONCLUSIONS: There is a significant familial component in the cause of
strabismus. Furthermore, there are important contributions to this familial
aggregation beyond those associated with known risk factors for strabismus.
