Front Matter

212 Autism and Exposure to Environmental Chemicals

the harmful effects on human health of some anti‐androgens, such as testos­

terone and estrogen, that might disturb human sex hormones without affecting

rodents may go unnoticed.

Dioxin levels in breast milk were associated with an increased risk of cryp­

torchidism in Danish boys [130,131]. Dibutyltin concentrations in placenta

were associated with an increased incidence of cryptorchidism in Danish boys.

A French case‐control study on cryptorchidism measured concentrations of

DDE, PCBs, di‐n‐butyl phthalate, and metabolite monobutyl phthalate (MBP)

in colostrum and cord blood (Figure 7.6, [132]). The boys in the high‐exposure

group (based on combined exposure to DDE and PCBs) had a higher risk of

cryptorchidism than boys in the lower exposure group [133]. A similar ten­

dency was found for MBP. A US study that examined testicular position at

the  mean age of 12.8 months reported an association between levels of

maternal urinary mono‐2‐ethyhexyl phthalate and incomplete testes descent

[134]. Maternal urinary levels of five phthalate metabolites were also associ­

ated negatively with anogenital distance (AGD; [135]), suggesting an anti‐

androgenic effect [134]. The Finnish–Danish study reported an association

between phthalate levels in mother’s milk and serum testosterone and lutein­

izing hormone (LH) concentrations at 3 months of age in boys, although

there  was no direct association between cryptorchidism and milk phthalate

Denmark

United kingdom

Finland

10.0

7. 5

5.0

2.5

0.0

1960 1980 2000

Year

Incidence of cryptorchidism (%)1. 8

2.7

3.5

2.1

5.0

8.5

Figure 7.14 Incidence of cryptorchidism at birth on the basis of prospective clinical studies

from the 1950s to the 2000s in Denmark, Finland, and the UK. The data points are marked

on the year of the publication of the study which represents the preceding incidence rate.

Source: Adapted from Ref. [129].