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The Search for Genes

Finding the Gene is the First Step in Understanding the Disease Process In almost every cell in our bodies, we have approximately 100,000 genes that govern the way our body develops and functions. We have two copies of each gene because we inherit one copy from our mother and another from our father. In humans, the genes are carried on 23 pairs of chromosomes. Each gene contains a specific DNA (deoxyribonucleic acid) sequence that codes for a specific protein.

Linkage Analysis
The search for disease causing genes generally begins with analysis of blood samples collected from multiple family members and multiple families. From that blood, we obtain the DNA. With enough samples from many families, we can often determine the chromosomal location of the gene likely to be responsible for the disease. This is called linkage analysis.

Candidate Genes
At the proposed location on the chromosome, there will often be many genes whose functions are not known. Therefore, next it is necessary to look at all the genes to find the best possible "candidate" for the one that causes the disease.

DNA Sequencing
Once this candidate gene is found, the exact DNA sequence is determined. The DNA samples from the affected individuals in each family are then examined for alterations in the DNA sequence. Some changes we find are "benign" and cause no change in the protein product. These are called polymorphisms. Other times the alteration causes a big change in the protein product which is then defective, or even absent. These changes are called mutations. Mutations are changes in the normal DNA sequence that lead to an abnormal protein product, and therefore an abnormal function of that protein.

Finding the gene is just the first step in understanding a disease process. Once the gene is found and the protein identified, it is then necessary to determine the protein's normal function and its abnormal function. It is only through these studies that we can then look at forms of intervention and therapy.

Department of Health and Human Services NIH, the National Institutes of Health