US researchers have reported firm evidence that damage to mammalian male fertility caused by transient exposure of embryos to endocrine-disrupting environmental toxins can be passed down to subsequent generations. Their finding is published this week by Science.

Investigators from Washington State University, Pullman, exposed female rats in mid gestation to two endocrine disruptors, the anti-androgenic vinclozolin and the estrogenic methoxychlor, both at higher doses than normally encountered in the environment.

More than 90% of male offspring had low sperm counts and abnormal sperm production, with 10% being completely infertile. An almost identical pattern of male fertility impairment was passed down to second-, third-, and fourth-generation males whose parents were not exposed to the toxins.

The critical process causing the loss of fertility was the DNA remethylation that always occurs at the time of gonadal sex determination shaping the patterns of gene expression in the offspring, said Michael Skinner,...

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