Understanding how Genes cause Disease

A genetic disorder is a disease caused by an abnormality in a person’s genetic material. This can be due to a single mutation in a gene, such as cystic fibrosis, or due to a chromosomal abnormality, such as Down’s syndrome.

A gene is a piece of DNA that encodes a protein. Proteins are molecules that play important roles in the physiology of a person. DNA is made up of a string of nucleotide bases. When the DNA is different from that of a normal person’s, due to a change in one nucleotide base, this can cause an abnormal protein to be made. The person then loses the function of the protein in the body, and this results in disease. In cystic fibrosis for example, the defect is in the protein called CFTR. This results in a defective chloride channel in the cell membranes in the lung, and excessive mucus builds up in the lung.

A mutation in a gene may be inherited from your parents. It may also arise spontaneously. Cancer is thought to arise from the accumulation of many of these mutations in the same cell.

Scientists have now discovered numerous single gene disorders and the hope is that gene therapy, where the defective gene is replaced by a normal gene, will be a future therapy for these diseases. Besides single gene disorders, there are many diseases that are thought to be due to both genetic and environmental factors, such as diabetes and heart disease. These diseases are thought to be due to variations in a combination of several or even many genes. The study of the genetics of such diseases are now becoming more intense as scientists have sequenced the entire human genome and can use this information to discover how genes cause disease.