Gene therapy, also called gene transfer, is an experimental treatment being researched for a variety of medical conditions, including diabetes. It involves the introduction of normal genes to alter, replace or supplement genes that are not functioning properly.

To understand gene therapy and how it can be used for diabetes treatment, several terms should be explained. These include:

• Chromosome. Rod-shaped element in the nucleus (center) of each cell. Chromosomes contain the hereditary information that guides all cell actions. Most human cells have 46 chromosomes, with a set of 23 inherited from each parent. Twenty-two of these pairs are common to males and females and are called autosomes. The 23rd pair, known as the sex chromosomes, determine a person’s sex (XY in males, XX in females).
  
  
• Gene. The basic unit of hereditary. Each gene is located in a specific site on a chromosome. Each human cell has about 20,000 to 25,000 genes. A person inherits two copies of each gene, one from each parent. They determine physical characteristics such as eye color and skin color, and genetic diseases such as maturity-onset diabetes of the young (MODY). Genes also contribute to other characteristics in which environment and behavior play a role, such as body weight, intelligence and the risk of multifactorial diseases (e.g., type 2 diabetes).
  
  
• Genome. All of the genetic material of a species. The human genome has about 20,000 to 25,000 genes.
  
  
• DNA (deoxyribonucleic acid). A complex substance in genes that contains genetic information needed to make the body’s proteins. These proteins allow the body to function and grow.
  
  
• Allele. Variations of a single gene. Differences in alleles are one factor involved in differences among people in physical characteristics and susceptibility to disease. Some alleles, traits and genetic diseases are dominant, others recessive. For instance, a person who has inherited a brown-eye gene from one parent and a blue-eye gene from the other parent will have brown eyes. Blue eyes are a recessive trait, meaning a person must have inherited that allele from each parent. MODY is an example of an autosomal dominant condition – a person who inherits a MODY gene from only one parent will have the disease.
  
  
• Vector. A substance, such as a virus or protein, used to supply genetic material to target cells. A gutless viral vector is a carrier from which the harmful genes have been removed.

Each chromosome contains long, tightly wound strands of DNA, which is the genetic blueprint for how the body is constructed and maintained. If the DNA strands within each chromosome were uncoiled and connected, the result would be more than 5 feet long (1.5 meters) but only a tiny fraction of an inch in width, according to the Human Genome Project, an international research project that mapped all human genes.

A strand of DNA is composed of only four types of chemicals called bases: adenine (A), cytosine (C), guanine (G) and thymine (T). The strands determine traits such as hair color or height. Segments of the DNA strand that have been identified as having specific effects on the body are called genes.

Strands of DNA are linked together at specific points along their length so that the base (A, C, G or T) on one strand is paired with a complementary base on the other strand. A pairs only with T, and G pairs only with C. When the bases are paired, they form base pairs. The human genome is estimated to contain 3 billion base pairs. Scientists once thought that humans had about 100,000 genes, but the Human Genome Project has reduced that estimate to less than 25,000.

The Human Genome Project finished mapping the human genome in 2003, but analysis of the data on this complete DNA blueprint will continue for years. The potential benefits are enormous. Mapping the human genome not only allows scientists to interpret genetic information, but also gives them a chance to potentially change the genetic information through gene therapy. These treatments could have revolutionary effects on the diagnosis and treatment of many diseases. People could have the opportunity to have certain genetic elements altered, which might offer cures or prevention for certain diseases.

Scientists have identified specific defective genes that cause some diabetic conditions, such as MODY and Wolfram syndrome. Researchers have also linked certain genes to risk of type 2 diabetes, type 1 diabetes and gestational diabetes but understand these connections less clearly.

Gene therapy holds the greatest promise for diseases caused by one defective gene, according to the U.S. National Institutes of Health. Examples include sickle cell anemia, cystic fibrosis (a disease that can lead to secondary diabetes), hemophilia, MODY and Wolfram syndrome. Gene therapy may also offer hope for conditions involving multiple factors, such as type 1 diabetes, type 2 diabetes, heart disease and cancer, and possibly infectious diseases such as AIDS.

Gene therapy is being developed at universities, research centers, corporations and medical centers around the world. Most of the studies are in early stages, and the research materials are not used in standard treatments. Several thousand people have taken part in trials of gene therapy in the United States, most for cancer but a small number for diabetes. The U.S. Food and Drug Administration (FDA) has not yet approved the sale of any gene therapy products.