Objective: To test the possible multifactorial-threshold model in the origin of isolated microtia/anotia (IMA).
Method: The observed number of IMA in the first degree relatives of cases affected was compared with the expected number of affected first degree relatives based on the multifactorial-threshold model in the population-based large dataset of the Hungarian Case-Control Surveillance of Congenital Abnormalities, 1980-1996.
Results: Of 354 cases with IMA, 14 (4.0%) had the affected first degree relatives with IMA. There was a low and similar rate of familial occurrence of IMA in parents and siblings of cases. The observed numbers of affected first degree relatives of cases with IMA and their expected numbers did not show significant difference (p=0.47). Some other findings (e.g. male excess and the interaction of triggering environmental factors with polygenic predisposition) confirmed this hypothesis.
Conclusions: The familial pattern of cases with IMA does not reject the hypothesis that the multifactorial-threshold model, i.e. gene-environmental interaction, may be the explanation for the origin of this congenital abnormality group, although the number of familial cases was quite small in the study.
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