Alteration within a single mutant gene may have consequences in various tissues in a given individual. The presentation of multiple phenotypic abnormalities in different organ systems produced by a single mutant gene is termed pleiotropism. For example:
Marfan syndrome: Ectopia lentis occurs with arachnodactyly, aortic aneurysms, and long extremities.
DIDMOAD (diabetes insipidus, diabetes mellitus, optic atrophy, and neural deafness) syndrome: Optic atrophy is found in association with juvenile diabetes mellitus, diabetes insipidus, and moderate perceptive hearing impairment.
Alport syndrome: Neurosensory hearing loss can be associated with hereditary hematuric nephritis, lenticular changes (anterior lenticonus, spherophakia, cataracts), arcus juvenilis, and whitish-yellow retinal lesions.
Bardet-Biedl syndrome: This is characterized by pigmentary retinopathy, obesity, genital hypoplasia, mental debility, and polydactyly.
In each of these disorders, a single mutant gene is responsible for dysfunction in multiple organ systems.
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.