The human genome is made up of approximately 30,000 genes. In each gene, there are exons and introns which are involved in forming mature messenger RNA. Messenger RNA or mRNA is translated into protein. Through different combinations and cutting of exons, genes may produce different mRNA and consequently different proteins. Thus, there are more proteins than genes in our cells. Significant changes, like deletion or insertion of nucleotides (called mutations), in gene structure, can lead to the production of abnormal proteins that may result in disease. Hereditary diseases occur when the changes in gene sequence are passed on to offspring. Polymorphism in coding regions of genes produce what are known as alleles and resulting changes in protein structure can increase the risk for diseases like hypertension and schizophrenia. Mutations which occur only in body cells (somatic cells) include cancer.
The human body recognizes the significance of DNA as the genetic material or the blueprint of life. Thus, a complex system of proteins provides support to the DNA replication process, making sure that genomic stability is maintained at all cost. Due to this system, DNA can be copied with high fidelity for billions of times. Few mutations occur during this process because the mistakes in copying and damage to DNA are sensed by several proteins which oversee the repair of the damage or death of the cells with the damaged DNA. When the genes for these guardian proteins become mutated, then genetic stability is destroyed. Inherited mutations predispose the cells to develop cancer and other irregularities in cell division. Genetic instability in cancer cells results in weaker cells with increased susceptibility to damage and further mutations which result in higher malignancy and resistance to treatment.
The genetic disease also results from defects in the regulation of gene expression.