In general, the human body can tolerate excess genetic material more easily than it can tolerate missing genetic material. In certain cases, such as Turner's Syndrome, if individuals are identified soon enough they can be successfully treated with hormones to reduce the effects of the chromosome imbalance. In some cases genetic material is missing from a chromosome. Deletion of the tips of chromosomes are called terminal deletions. The most common deletions observed in humans are those that remove small portions of a chromosome.
Larger deletions lead to death.