ASSOCIATIONS BETWEEN SIBLINGS FOR ESOTROPIA AND EXOTROPIA

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 generalize d estimating equations approach to logistic regression was used to est imate familial aggregation of esotropia and exotropia. Results: For an y pair of siblings, the odds for one sibling having esotropia more tha n doubled when the other sibling had esotropia. For exotropia, there w ere differences in sibling associations based on birth relationships. In particular, there was no statistically significant association be t ween siblings from separate single births. On the other hand, for the pairs of siblings from multiple births (ie, twins, triplets, and quadr uplets), the odds for exotropia in one sibling were increased by at le ast a factor of 17 when the other sibling from that birth also had exo tropia. For both esotropia and exotropia, adjustment for previously id entified risk factors only somewhat reduced the magnitudes of the obse rved associations. Limited data on zygosity showed a stronger associat ion between monozygotic twins than between dizygotic twins. Conclusion s: There is a significant familial component in the cause of strabismu s. Furthermore, there are important contributions to this familial agg regation beyond those associated with known risk factors for strabismu s.