OBJECTIVE: To study concordance rates of cryptorchidism (undescended testis) in pairs of boys with varying family structure, to evaluate the risk contribution from the intrauterine environment and genetic factors. DESIGN: Population based study of 1,024,500 Danish boys born from January 1, 1973 to December 31, 2004. Classic twin method and computerized square dance design. SETTING: Hospitals and outpatient clinics. PATIENT(S): Six groups of boy pairs: boys with no relation, paternal half-brothers, maternal half-brothers, full brothers, dizygotic twin brothers, and monozygotic twin brothers. INTERVENTION(S): Observational study. MAIN OUTCOME MEASURE(S): Status on each individual regarding cryptorchidism and orchiopexy from the Danish National Patient Register. RESULT(S): Concordance rates of cryptorchidism in the groups were as follows: boys with no relation 3.2% (95% confidence interval 2.7%-3.6%), paternal half-brothers 3.4% (2.3%-4.7%), maternal half-brothers 6.0% (4.5%-7.7%), full brothers 8.8% (8.3%-9.8%), dizygotic twin brothers 24.1% (16.0%-33.6%), and monozygotic twin brothers 27.3% (15.5%-41.2%). CONCLUSION(S): The concordance rate was higher in maternal than in paternal half-brothers, and much higher but of equal magnitude in both twin groups. The findings strongly support that the intrauterine environment and maternal inheritance are contributing to the occurrence of cryptorchidism.
Fertility and Sterility, 2010, Vol 93, Issue 1, p. 124-129