How genes and the environment shape health and disease.
Genetics and genomics both play roles in health and disease. Genetics is the study of genes and how traits or conditions are passed down from one generation to another. Genomics is the study of all of a person’s genes — the genome.
Genetics refers to the study of genes and their roles in inheritance — the way certain traits or conditions are passed down between generations. Genes (units of heredity) carry the instructions for making proteins, which direct the activities of cells and functions of the body. Examples of genetic or inherited disorders include cystic fibrosis, Huntington’s disease, and phenylketonuria (PKU).
Genomics is a more recent term describing the study of all of a person’s genes, including interactions of those genes with each other and with the person’s environment. It includes the study of complex diseases such as heart disease, asthma, diabetes, and cancer — conditions typically caused more by a combination of genetic and environmental factors than by individual genes. Genomics is opening new possibilities for therapies, treatments, and diagnostic methods.
Genetics helps individuals and families learn how conditions such as sickle cell anemia and cystic fibrosis are inherited, what screening and testing options exist, and, for some conditions, what treatments are available.
Genomics is helping researchers discover why some people get sick from certain infections, environmental factors, and behaviors while others do not. Some people exercise their whole lives, eat well, and still die of a heart attack at 40; others smoke, never exercise, and live to 100. Genomics may hold the key to understanding these differences.
Apart from accidents, genomic factors play a role in nine of the ten leading causes of death in the United States, including heart disease, cancer, and diabetes. All human beings are 99.9 percent identical in their genetic makeup — the differences in the remaining 0.1 percent hold important clues about the causes of disease. A better understanding of how genes and the environment interact is helping researchers find better ways to improve health and prevent disease.
Understanding diseases caused by a single gene (using genetics) and complex diseases caused by multiple genes and environmental factors (using genomics) can lead to earlier diagnoses, interventions, and targeted treatments. A person’s health is influenced by family history and shared environmental factors, which makes family history a powerful, personalized tool — a cornerstone for learning about genetic and genomic conditions and for developing individualized approaches to prevention, intervention, and treatment.
The suffix “-ome” comes from the Greek for all, every, or complete. The DNA sequence of genes carries the code for building proteins; this DNA is transcribed into RNA, which is translated into proteins. Proteomics is the large-scale analysis of all the proteins in an organism, tissue type, or cell (the proteome). It can reveal specific, abnormal proteins that lead to diseases such as certain forms of cancer.
These terms describe the intersection of pharmacology and genetic variability in determining an individual’s response to particular drugs. Pharmacogenetics deals with variability in drug response due to variation in single genes, with the goal of creating individualized drug therapy — the best choice and dose of drugs. One example is the breast cancer drug trastuzumab (Herceptin), which works only for women whose tumors overproduce a protein called HER2.
Pharmacogenomics is similar but typically involves the search for variations in multiple genes, and can examine the entire genome rather than single genes. These studies are leading to drugs that can be tailor-made for individuals and adapted to each person’s genetic makeup — working better and with fewer side effects than one-size-fits-all drugs. For example, the FDA recommends genetic testing before giving the chemotherapy drug mercaptopurine (Purinethol) to patients with acute lymphoblastic leukemia, because some people have a genetic variant that interferes with processing the drug.
Stem cells have two important characteristics: they are unspecialized cells that can develop into various specialized body cells, and they can stay unspecialized and make copies of themselves. Embryonic stem cells come from the embryo at a very early stage (the blastocyst); adult stem cells come from more developed tissues like umbilical cord blood, circulating blood, bone marrow, or skin.
Researchers are investigating the use of stem cells to repair or replace damaged tissues, similar to whole-organ transplants. Because stem cells may carry less risk of immune rejection, the therapy may be more successful. Stem cells have been used experimentally to form cells of the bone marrow, heart, blood vessels, and muscle, and since the 1990s umbilical cord blood stem cells have been used to treat children with certain anemias and leukemias — for example, stem cell transplantation for childhood acute lymphoblastic leukemia.
Cloning can refer to genes, cells, or whole organisms. A cell clone is any genetically identical cell descended from a single common ancestor; gene cloning makes multiple identical copies of a single gene. There are two major types relevant to humans or animals: therapeutic cloning, which grows cloned cells or tissues from an individual (for example, new liver tissue for a patient with liver disease, typically using stem cells), and reproductive cloning, which generates an entire animal with the same nuclear DNA as another — as with Dolly the sheep. Success rates for reproductive animal cloning have been very low.