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.

Genes and Environment play roles in diseases. Image: Newscom

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.

Inspired by Diabetes Notes’ "Putting a Face on Diabetes", I wanted to do the same and show how people with genetic disorders - rare or common - manage their condition and live their lives to the full.

I found a feature article about a teenager named Lizzie Tinney, living with Xeroderma Pigmentosa or XP. Lizzie is only 13 years old and yet she already had to undergo surgeries to remove skin cancer sores. Even while wearing protective clothing from head to tow, Lizzie still has to carry around a meter to measure how much UV light she receives.

"It’s way hard. Its way still hard because I love the sun," says Lizzie. "But now that I know that I have XP, I can just go out with my hood on and I go out and play."

Xeroderma Pigmentosa is a rare genetic disorder in which the skin is unable to repair the damage caused by ultraviolet radiation, such as such exposure. The skin becomes so sensitive to UV rays that it gets thin and pigmented. The DNA damage accumulates with age and is so irreversible that risk for skin cancer is 2000-fold.

To find out more about Xeroderma Pigmentosa, visit the Xeroderma Pigmentosum Society website.