Genetic disease results from a mutation in the sequence of a genome.
Genetic mutations which cause disease are due to the mutation not allowing a protein to form correctly.
Not all mutations cause disease, some are neutral or beneficial.
Chromosomal genetic damage is caused by large amount of damage to one or more chromosomes resulting in mutations which may not be compatible with life.
Monogenic disease is a single gene that is responsible for the disease. Polygenic disease is a combination of multiple genes that are responsible for the disease.