Answer: were.... susceptible to the effects of early-childhood mistreatment
This is an example of gene expression
Explanation: Monoamine oxidase deficiency is a disorder almost exclusively affecting males. It is characterized by behavioural problems and reduced intellectual ability which may manifest from early childhood. Most boys with this deficiency have poor impulse control and are susceptible to violent outbursts.
Although this deficiency is caused by mutations in the MAOA gene, researchers believe that some environmental factors such as maltreatment in early childhood may affect the severity of the condition and its accompanying behavioural problems.
Some studies suggest monoamine oxidase deficiency alters normal development of certain parts of the brain as monoamine oxidase is important in brain development, this may further contribute to reduced intellect and poor impulse control.