Hypospadias is a birth defect of the penis in which the position of the opening is shifted from its normal place on the head of the penis to somewhere along the shaft. The most extreme forms of hypospasias find the opening at the base, or even in the scrotum. Modest cases of this debilitating birth defect can be corrected through reconstructive surgery, but the most extreme cases sometimes cannot. The cause of hypospadias in humans has not been established, other than to observe that it must result from a developmental error in the womb that has prevented complete masculinization of the reproductive tract.

Experiments with laboratory animals reveal that hypospadias can be repeatedly and reliable produced by exposure to several endocrine disrupting chemicals, including DDE and vinclozilin, a commonly used fungicide.

The US Centers for Disease Control undertook a study of the rate of hypospadias in the US because of these animal studies. They had become concerned about endocrine disruption and decided that if it were a real problem, then there should be evidence in US health trends. They surveyed the animal studies looking for a reliable effect produced by endocrine disruption that, were it expressed in humans, would be readily and reliably detected. They were particularly interested in finding a health endpoint in which any changes in rate measured over time would not have been a result of differences in diagnosis or detection. This is a classic problem in longitudinal health studies. They selected hypospadias to study because it met these criteria.

The CDC's analysis of the changes in the frequency of hypospadias in the United States revealed a striking pattern: the rate has more than doubled since 1970. Indeed by 1993, hypospadias was detected in one out of every 125 boys born in the United States (graph, above).

Subsequent research has also revealed increases in hypospadias in several other countries, particularly Japan and Scandinavia. Data analyzed by Leonard Paulozzi of the US CDC indicates that the increase in hypospadias in some industrialized countries may have leveled off in the mid-1980s.

Research published in 2002 suggests but does not prove an ambiguous link to exposure to DDE in the womb. The study involved an analysis of umbilical cord blood kept frozen since it had been sampled during the period 1959-1965. More...