People who were abused or mistreated in their childhood and adolescence are prone to aggression and addictive behavior. Apparently, such childhood traumas have a negative effect on serotonin levels and reinforce alcoholism. However, the extent to which this occurs is still unclear.
A short, relatively clumsy text about the study – but afterwards a detailed, interesting interview.
Source (german): Childhood emotional abuse. The role of serotonin in alcoholism
Found at Alkohol adé (german)