Which teratogen is associated with yellow-brown discoloration of deciduous teeth?

The teratogen associated with yellow-brown discoloration of deciduous teeth is tetracyclines. Tetracyclines are a class of antibiotics that can cause permanent discoloration of the teeth when administered to a developing fetus or to young children whose teeth are still forming. This effect occurs because tetracyclines can bind to calcium ions in the body, incorporating into the enamel and dentin of the teeth, leading to the characteristic yellow-brown staining.

In contrast, while alcohol is known to have several teratogenic effects, including fetal alcohol syndrome, it does not specifically cause the yellow-brown discoloration of teeth. Thalidomide is primarily associated with limb abnormalities and other severe malformations rather than dental issues. Isotretinoin, used for severe acne, can also cause significant birth defects but is not related to tooth discoloration. Thus, tetracyclines are uniquely linked to the discoloration of deciduous teeth among the choices provided.