Which teratogen is associated with learning and behavioral differences, particularly noted for features like ptosis and short palpebral fissures?

The teratogen associated with learning and behavioral differences, especially characterized by features such as ptosis and short palpebral fissures, is alcohol. Fetal Alcohol Spectrum Disorders (FASD), which result from prenatal alcohol exposure, can lead to a range of neurodevelopmental issues and physical anomalies. Key features often observed in individuals with FASD include distinct facial characteristics like a smooth philtrum, thin upper lip, and the aforementioned ptosis (drooping of the eyelids) and short palpebral fissures (the horizontal eye openings).

Alcohol interferes with normal fetal growth and brain development during pregnancy, which can lead to cognitive deficits and learning disabilities. Therefore, the identification of specific physical markers, including ptosis and short palpebral fissures, alongside learning and behavioral challenges underscores the critical impact of alcohol as a teratogen during pregnancy.

Other substances listed, such as ACE inhibitors, lithium, and methylmercury, have their own teratogenic effects but do not present with the same characteristic features or the specific pattern of learning and behavioral issues associated with prenatal alcohol exposure.