Genetics is the study of heredity and the variations in inherited characteristics and diseases. Although genetics is a relatively new science compared with such disciplines as anatomy and physiology, its significance in the overall understanding of human life cannot be overstated. Genetic knowledge can enhance our understanding of the processes of cellular function, embryology, and development, as well as our concepts of disease. Many researchers think that as much as 90% of medical disease either has a major genetic component or involves genetic factors that may significantly influence the disease.
The discovery of previously unknown genes, such as the homeobox genes (eg, the HOX and PAX gene families)—which regulate, guide, and coordinate early embryologic development and differentiation—has opened new areas of understanding of physiology at the cellular or tissue level. (These genes, also called homeotic selector genes, are discussed in Part II, Embryology, as well.) Another example is the identification of the genes that appear to be transcribed as initiating events in the process of apoptosis, or programmed cell death, which itself appears crucial for normal embryogenesis as well as for degenerative diseases and cancers.
Genetic disorders affect about 5% of live-born infants in the United States. Approximately 50% of childhood blindness has a genetic cause. Some 20,000–25,000 human genes involving about 180,000 exons are known. In 10%–15% of known genetic diseases, clinical findings are limited to the eye; a similar percentage includes systemic disorders with ocular manifestations.
Familiarity with the vocabulary of genetics and molecular biology will greatly enhance the reader’s understanding of the following 2 chapters on molecular and clinical genetics. The reader is thus encouraged to review the genetics glossary in the appendix of this book, which includes many key genetics terms, as well as to consult online resources, 2 examples of which follow.
Excerpted from BCSC 2020-2021 series: Section 2 - Fundamentals and Principles of Ophthalmology. For more information and to purchase the entire series, please visit https://www.aao.org/bcsc.