Genetic Diversity & Lupus
Genetics and Lupus
Most people who have systemic lupus erythematosus, aka SLE or lupus, do not have any relatives who also have lupus. Lupus is familial in only 12-15% of cases. It is clear that lupus varies from one ethnic group to another.
SLE is thought to be a genetically complex disease, meaning that several different genes are involved in its development. Scientists suspect that tens, or even hundreds, of genes may be involved. According to recent genome-wide genetic scans, these genes may vary depending on a patient's ethnicity or the disease symptoms from which the patient suffers. For this reason, it is important for families of all ethnic backgrounds to participate in lupus research.
While several genomic “hot spots” are currently being explored, some of the genes have clearly been identified, e.g. FcgammaRIIA ; FcgammaRIIIA; complement components C2, C4 and C1q; PDCD-1; and HLA-DR. (A "hot spot" is an area where scientists believe it is extremely likely lupus genes exist.)
The Inheritance of Lupus
Many researchers think that lupus is hereditary, meaning it is passed on genetically from one generation to another. The pattern of inheritance is, however, unclear. It is known that not everyone who has the lupus genes develops the disease, as demonstrated in numerous identical twin studies. The rate at which both identical twins are affected with lupus varies from 15-69%.
This information indicates, first, that people who have lupus genes have a genetic predisposition to the disease. Merely having lupus-linked genes is not enough to cause a person to develop lupus. This in turn indicates that an external or environmental trigger is also involved in lupus disease onset in people with the genetic predisposition. (Known triggers include stress, hormonal changes, illness, certain viruses including Epstein-Barr virus and chemical exposure.)
Lupus Genes -- How They are Studied
Lupus Geneticists have been conducting familial studies of lupus for a decade. They study families that are both multiplex and simplex for lupus. These two kinds of families are useful in different ways for finding the lupus genes. Multiplex family research allows for the study of inheritable lupus, or lupus that is passed on genetically. These studies use DNA samples (usually blood) from the lupus patients and other unaffected family members whose relationships may prove useful for genetic linkage, usually parents, siblings, grandparents, etc. Simplex family research allows for the study of randomly-occurring lupus, or cases in which the lupus-associated genes come together arbitrarily to create a predisposition to disease. These studies use DNA samples (usually blood) from nuclear families, typically a lupus patient, 1-2 siblings and their parents.
By examining the genes of multiplex lupus families (comparing the genes of those affected by lupus and the genes of their unaffected family members) scientists are locating “hot spots” within the human genome worthy of more specific study. Multiplex lupus studies have also benefited from the sub-grouping of families, or grouping families according to certain characteristics that they share in common (i.e.-ethnicity, lupus patients' symptoms, patient gender) to find genes that may be specific to these groups or symptomologies.
More recently, geneticists have been able to capitalize upon the information available from Single Nucleotide Polymorphisms (SNPs). A SNP (pronounced "snip") is a single genetic variation that can occur within an individual's DNA; these differences make each person's genetic code unique. SNPs are pretty rare, occurring in just under 1% of the DNA bases in the human species. If they occur in the part of a person's DNA that codes for protein production, then SNPs may alter the biological function of the protein. In order to use SNP technology effectively, lupus “hot spots,” often discovered via multiplex family studies, are used as candidate areas for SNP study.
Some lupus “hot spots” for lupus genes currently under analysis include the following with other associated features:
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