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American Journal of Epidemiology Advance Access originally published online on November 27, 2007
American Journal of Epidemiology 2008 167(3):251-256; doi:10.1093/aje/kwm317
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American Journal of Epidemiology © The Author 2007. 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 Hypospadias: A Cohort Study

Tine H. Schnack1, Slobodan Zdravkovic1, Charlotte Myrup1, Tine Westergaard1, Kaare Christensen2, Jan Wohlfahrt1 and Mads Melbye1

1 Department of Epidemiology Research, Statens Serum Institut, Copenhagen, Denmark
2 Institute of Public Health, University of Southern Denmark, Odense, Denmark

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

Received for publication June 4, 2007. Accepted for publication September 27, 2007.

Hypospadias is one of the most common birth defects. However, its etiology remains largely unknown. The authors investigated the contribution of genetic and environmental factors to familial aggregation of hypospadias. Using Danish health registers, they identified 5,380 boys diagnosed with hypospadias in a cohort of 1,201,790 boys born in 1973–2005. Using binomial log-linear regression, they estimated recurrence risk ratios of hypospadias for male twin pairs and first-, second-, and third-degree relatives of a hypospadias case, which were 50.8 (95% confidence interval [CI]: 34.2, 75.5), 11.6 (95% CI: 9.75, 13.7), 3.27 (95% CI: 2.47, 4.34), and 1.33 (95% CI: 0.94, 1.88), respectively. Recurrence risk ratios did not differ for family members of a hypospadias case related to the same degree. In addition, the authors found no difference in the recurrence risk ratio for maternal compared with paternal second- and third-degree relatives of a hypospadias case. In conclusion, hypospadias was found to have a strong familial component and also to aggregate within more-distant relatives. Importantly, hypospadias was equally transmitted through the paternal and maternal sides of a family, and recurrence risk ratios for brothers and sons of a hypospadias case were similar. These findings indicate that genetic rather than intrauterine environmental factors have a principal role in causing familial hypospadias.

cohort studies; family; genetics; hypospadias; inheritance patterns

Abbreviations: A, additive genetic factors; C, shared environmental factors; CI, confidence interval; D, dominant genetic factors; E, nonshared environmental factors; RRR, recurrence risk ratio


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