What causes chemical imbalance? can you develop it or born with it?

I assume you mean in: Reference to psychiatric illness. They can occur due to genetic influences (hereditary) or from stress (external events, internal ways of thinking) or most likely from both in most cases (also called the "stress diathesis model" of mental illness. We should never forget the tremendous psychiatric toll taken on humanity by man's inhumanity to man, child abuse, war, torture, domestic/street violence.