-A curious visitor at The Tech
July 19, 2005
The chances of a parent with lupus passing it to her children are less than 5%. If lupus affects a second degree relative like an aunt or a grandma, then the chances are even lower.
So, is lupus genetic? Partly. Evidence definitely suggests that genes play a part. But the environment plays a role too.
Identical twin studies showed that genes and the environment are both involved. Remember, identical twins share the exact same DNA. So if lupus were purely genetic, then if one twin had lupus, the other one always would too.
This isn't the case. When one identical twin has lupus, the other twin has it only 24-69% of the time (depending on the study). Since this is higher than the 5% chance for any two siblings to both have lupus, genes are clearly involved. But something else must be going on too.
Scientists believe that the something is some sort of environmental trigger. No one knows what the triggers are for lupus. Scientists have proposed certain medications, smoking, too much stress, viruses, or even too much sun. But none of these has been proven.
How might something like a viral infection and certain genes work together to cause lupus? Let's look at a hypothetical case.
Jane has a set of genes that can lead to lupus but she doesn't have it yet. She gets a virus and her body's immune system mounts an attack.
She wipes out the virus and gets better. But, her immune system has been trained to look for anything that looks like the virus and attack. Unfortunately for Jane, her set of lupus alleles has made her joints look like the virus.
Jane's immune system now goes after her joints, thinking it is a viral invader. If Jane had never been infected, then she may never have developed lupus. She needed the unlucky combination of genes and environment to get lupus.
And the need for a trigger isn't the only reason lupus is not passed down easily. Another reason is that there is actually more than one gene involved.
This decreases your chances because you don't have to inherit only a single gene that could lead to lupus. Current estimates put the number at four or more genes.
Why would this matter? Remember, genes come in different versions called alleles.
For genes that can cause a disease, there are often two forms -- one that can lead to the disease and one that doesn't. If you don't have lupus but it runs in your family, then one or more of your"lupus" genes may be of the type that doesn't cause lupus.
So in order to pass down lupus, you would need to have a partner who has the missing lupus causing genes. And if lupus doesn't run in your partner's side of the family, then the chances are smaller.
As you can see, lupus is partly genetic. Certain versions of more than one gene predispose a person towards developing lupus. But something needs to happen to trigger it as well.