As scientists decode the information stored in our genes, they’re learning more about the roots of disease. How many human diseases have DNA markers? Your DNA can indicate whether you have a predisposition for a certain disease. There are 30,000 genes — distinct sequences of atoms — making up the body’s DNA. Genes tell our cells to produce the proteins we need to live. Many diseases — like cystic fibrosis and sickle cell anemia — happen when a gene mutates and manufactures defective proteins. At the moment, scientists can test patients for about 500 diseases by checking for mutated genes. But, for the most part, diseases caused by a single mutated gene are very rare. And the genetic tests for more common diseases with a genetic component — say, heart disease, some cancers, autism and schizophrenia — don’t yet exist. These diseases result from the interplay of many different genes, but they’re also affected by a person’s environment. Diseases from invading viruses and bacteria might have a genetic component, too — in the sense that whether you become infected might depend on how robust your immune system is — and that heartiness or lack of it depends, in part, on your genes.
- A resource primarily for health-care professionals, but also for people with specific questions about certain genetic diseases – Genetests
- Ever want to see exactly where certain disease causing genes lurk? This site is a little hard to use, but you can use it to link to gene maps available elsewhere – Online Mendelian Inheritance in Man
- Story from the NIH about cystic fibrosis
It’s probably a good idea to clarify the term “gene markers”. In the script, we used the term loosely – and focused on the question of how many human diseases are linked to genes. A more technical use of the term “gene markers” refers to sections of DNA that scientists use to hunt for disease-causing genes.
These sections of DNA may have nothing to do with causing the disease itself. But they are often associated with the disease — that is, they commonly turn up in people with a certain disease. Scientists use these markers as signposts — they assume the disease-causing gene is probably near to the marker, so the researchers scrutinize nearby genes.
Genetic mutations sometimes lead to disease — but sometimes these mutations can be helpful. For example, if a child inherits only one copy of the cystic fibrosis gene, he or she may be better able to resist the typhoid bacteria. And if a child has only one copy of the sickle cell gene, he or she is more resistant to malaria. Only some diseases, like sickle cell anemia — which warps a patient’s blood cells — occur when a person is born with a mutated copy of a single critical gene. Other diseases, like cancer, arise from the interplay of many genes.
The eruption of cancer is often influenced by environmental conditions, like a person’s diet or his exposure to harmful chemicals. And remember that genes give the blueprint for our immune system — if our genes give us a lousy one, we could be more susceptible to certain bacteria or viruses.