Isabelle's baby was born blind, deaf, and with heart defects and brain damage. most likely isabelle was exposed to during her pregnancy.

Mutagens

Mutagen includes Chemicals and Radiations.
Mutagens causes alterations to the DNA of cells called mutation. These mutations when accumulated, could cause problems like blindness and many defects. Thus, an overall accurate answer is mutagen (an umbrella term that includes substances that causes mutations).