When I tell people I used to research about the genetics of myopia (or nearsightedness), one of the questions they ask is whether they’ll pass it to their children.
And I tell them there are other factors, “interactions” we call them, between our genes and our environment that determine if certain genes will express and/or be passed to our children.
For example, mutations in the brca1 gene are highly associated with very high risks of breast cancer. A brca1 (breast cancer 1; on chromosome 7) is one of the genes in the body that suppresses tumors, by repairing damaged DNA. A mutation or defect in the gene produces a protein that can not repair DNA in other genes. A person with brca1 mutations has up to 80% risk of having breast cancer in one’s lifetime.
However, not everyone who has breast cancer has the brca1 mutation. So, there must be other causes or factors that brought about cancer, which may have nothing to do with brca1. Some of the environmental risk factors for developing breast cancer include recent use of birth control pills; earlier start to the menstrual period; postmenstrual hormone therapy, alcohol and many others (see list here).
Disorders that may be affected by genes and environment (risk factors) include other cancers, autism and other behavioral conditions, eye diseases like myopia, asthma and allergies, heart diseases, obesity… the list goes on. Genetics parlance refers to these as “complex disorders“.
In contrast, there are medical conditions that are 100% genetic, referred to as “Mendelian disoders“. Having a defective gene means the person is affected by the disease, and passes the gene to his/her children. These disorders can be diagnosed before birth, usually through a genetic screening test at pregnancy. Examples include downs syndrome, cystic fibrosis, thalassemia, phenylketonuria, sickle cell anemia, hemophilia A, Tay Sachs’ disease.
What I’d like to do this month is look at some of the complex disorders and the environment and genetic risk factors involved. We’ll start with myopia or nearsightedness, but let me know if there is a disease you’d like me to focus on as well.