SNP Shot: Genomic Insights

Myopia, or nearsightedness, is a common visual impairment where distant objects appear blurry. Individuals with this condition find it more difficult to see objects at a distance (e.g., while driving) than those that are close (e.g., when reading or using a computer). Untreated nearsightedness can result in squinting, eyestrain, headaches, and significant vision problems, but can be corrected with glasses, contacts, or surgery.

Nearsightedness typically develops during childhood or adolescence. It often progresses until adulthood, at which point it tends to stabilize. In some instances, nearsightedness can improve later in life.

Normal vision occurs when light passes through the cornea, the clear front part of the eye, and is focused by the lens onto the retina. The retina, located at the back of the eye, contains light-sensitive cells. In nearsighted individuals, the eyeball is often elongated. This causes light to focus in front of the retina, rather than directly on it, resulting in blurry distance vision. The longer the eyeball, the more pronounced the nearsightedness.

The severity of nearsightedness is measured in diopters, which indicate the lens power required for correction. Nearsightedness is corrected using negative (minus) lenses. A higher diopter value signifies more severe nearsightedness. It's possible for one eye to be more nearsighted than the other.

Eye doctors often classify nearsightedness less than -5 or -6 diopters as "common myopia." Nearsightedness of -6 diopters or greater is typically classified as "high myopia." This distinction is important because high myopia increases the risk of other eye conditions that can lead to permanent vision loss, including retinal tears or detachment, cataracts (clouding of the lens), and glaucoma (a disease typically linked to increased pressure within the eye). The risk of these complications increases with the degree of nearsightedness. "Pathological myopia" refers to cases where high myopia causes tissue damage within the eye.

Inheritance:

Common myopia is a complex condition influenced by numerous genes and doesn't usually have a clear inheritance pattern. Individuals with a first-degree relative (e.g., sibling or child) with nearsightedness have an increased risk of developing it compared to the general population. This elevated risk is likely due to both shared genetic factors and shared environment and lifestyle factors within families.

Similar to common myopia, high myopia typically lacks a clear inheritance pattern. However, when caused by a mutation in a single gene, it can follow autosomal dominant, autosomal recessive, or X-linked inheritance. Autosomal dominant inheritance requires only one copy of the mutated gene to cause the condition; often, the affected individual inherits the mutation from a parent with the condition. Autosomal recessive inheritance requires two copies of the mutated gene; each parent carries one copy, but usually doesn't exhibit symptoms. X-linked inheritance involves genes on the X chromosome. Males, with only one X chromosome, are affected if that copy contains the mutation. Females, with two X chromosomes, may have milder or no symptoms when one copy is mutated. Males are generally more frequently affected by X-linked disorders. If nearsightedness is a feature of a genetic syndrome, it will follow the syndrome's inheritance pattern, usually autosomal dominant, autosomal recessive, or X-linked.