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American Journal of Epidemiology Advance Access originally published online on April 23, 2008
American Journal of Epidemiology 2008 167(12):1453-1457; doi:10.1093/aje/kwn081
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American Journal of Epidemiology © The Author 2008. Published by the Johns Hopkins Bloomberg School of Public Health. All rights reserved. For permissions, please e-mail: journals.permissions@oxfordjournals.org.

ORIGINAL CONTRIBUTIONS

Familial Aggregation of Cryptorchidism—A Nationwide Cohort Study

Tine H. Schnack, Slobodan Zdravkovic, Charlotte Myrup, Tine Westergaard, Jan Wohlfahrt and Mads Melbye

From the Department of Epidemiology Research, Statens Serum Institut, Copenhagen, Denmark

Correspondence to Dr. Tine Schnack, Department of Epidemiology Research, Statens Serum Institut, Artillerivej 5, 2300 Copenhagen S, Denmark (e-mail: tsh{at}ssi.dk).

Received for publication December 7, 2007. Accepted for publication March 11, 2008.

Although cryptorchidism is the most common birth defect in boys affecting 4–9 percent of newborns and 1–2 percent of boys 1 year of age, the etiology remains largely unknown. The authors investigated the contribution of genetic and environmental factors to familial aggregation of cryptorchidism. Using Danish health registers, they identified 25,395 boys diagnosed with cryptorchidism in a cohort of 1,022,713 boys born in 1977–2005. Using binomial log-linear regression, they estimated recurrence risk ratios (RRRs) of cryptorchidism for male twin pairs and first-, second-, and third-degree relatives of a cryptorchidism case. The RRR in same-sex twins was 10.1 (95% confidence interval (CI): 7.78, 13.1). The RRR among first-degree relatives was significantly higher among brothers (RRR = 3.52, 95% CI: 3.26, 3.79) than for offspring of a cryptorchidism case (RRR = 2.31, 95% CI: 2.09, 2.54). The RRR was also found to be significantly higher in maternal (RRR = 2.12, 95% CI: 1.74, 2.60) than paternal (RRR = 1.28, 95% CI: 1.01, 1.61) half brothers. In conclusion, inherited factors were found to have a moderate influence on the risk of cryptorchidism. The data are compatible with the hypothesis that maternal factors operating in utero are important for the risk of cryptorchidism.

aggregation; cohort studies; cryptorchidism; Denmark; familial data; heredity; twins

Abbreviations: CI, confidence interval; RRR, recurrence risk ratio


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