Researchers tracked 168 sets of newborn twins and seven sets of newborn triplets for two years. They compared episodes of middle ear disease in identical siblings with those in siblings who were not identical that is, those who shared some but not all the same genes.
Identical siblings were found to suffer far more similar rates of recurrent middle ear effusion, a buildup of fluid that can impede hearing and speech development, than were nonidentical siblings.
The researchers calculated that heredity accounts for 73 percent of susceptibility to middle ear effusion in children under 2.
The study, led by Dr. Margaratha Casselbrant of the University of Pittsburgh School of Medicine, was published in Wednesday's Journal of the American Medical Association.
Middle ear infections are the most common illness in children next to the common cold. Previous research has shown that environmental factors can increase a child's vulnerability, including cigarette smoke and bottle feeding rather than breast-feeding.
An editorial by experts not involved in the study said the findings indicate that siblings of children prone to ear infections should be monitored more closely. That could include more frequent hearing tests and perhaps more aggressive treatment to head off problems with hearing and development of speech and thinking ability, wrote Garth D. Ehrlich and Dr. J. Christopher Post of Allegheny General Hospital in Pittsburgh.