Genetics in Lupus
Dozens
of studies have been carried out looking at family histories of lupus and these
studies have to be interpreted cautiously. Studies solely based on
questionnaires are not necessarily sufficient. They need to be supplemented with
blood test samples. There does seem to exist a small but definite genetic
tendency. The most common finding in these clinical studies has been the
presence of an increased number of patients with mild or minimal lupus amongst
the relatives of patients attending clinics. There is also an increased number of
patients' relatives with various antibodies that have no medical features of the
disease but only the blood test markers. In addition, studies have revealed evidence of
an association with tissue type and there seems to be a statistical association
in lupus with certain blood groups, notably HLA, B8 and DR3. Even more
interesting is the finding of a rare "complement" abnormality. Looking
at the sixth chromosome is the marker for a development of a blood protein
called complement. Some eight per cent of lupus patients have an absent or
"C4 null" genetic marker for complement. Complement is one of the
protective mechanisms against outside invasion by, for example, viruses. This
may offer a partial explanation for the development of lupus in these
genetically susceptible individuals.