Complement susceptibility factors in atypical haemolytic uraemic syndrome, age related macular degeneration and ageing.
Lead Research Organisation:
Newcastle University
Department Name: Institute of Cellular Medicine
Abstract
Haemolytic uraemic syndrome (HUS) is usually a serious complication of infection with the bacteria E.Coli O157. This organism causes a severe gastrointestinal infection from which recovery is usual. However, 5-10% of patients develop kidney failure. This is secondary to a bacterial toxin which attaches itself to the lining of blood vessels in the kidney causing them to become blocked. Most patients recover but in a few the illness is severe enough to cause death.
There is a rarer form of HUS , called atypical, which is not associated with E.Coli O157 infection. Atypical HUS (aHUS) has two variants, sporadic and familial. The sporadic form occurs often without any preceding illness but can be associated with use of certain drugs (most notably the oral contraceptive), pregnancy and HIV infection. Recovery of kidney function is less common and many patients require long term dialysis. In the familial form several members of a family will, over a period of time, be affected in a way similar to the sporadic form.
We have found abnormalities in the genes for four proteins, called factor H, membrane cofactor protein, factor I and C3 in approximately 50% of aHUS. These all belong to a common group of proteins, named complement. They have an important role in allowing the body to differentiate between its own and foreign cells. If any of these genes is faulty then the body?s own cells can be damaged by mechanisms designed to destroy foreign cells.
There is evidence that in a small number of patients with aHUS that there are faults in more than one of these genes. We have DNA samples from nearly 250 patients with aHUS and wish to screen all the known genes even in those patients in whom we have already found one fault.
We have recently found that the structure of the chromosome on which these genes lies is in some individuals with aHUS rearranged to form new genes, the presence of which predispose to the disease. We have also found that such rearrangements can lead to loss of genes and that this can predispose to another more common disease called age related macular degeneration. This is the commonest form of blindness in the elderly and has been shown to be associated with the factor H gene. We now wish to determine what the biological effect of loss of these genes is and whether it is more common with increasing age.
There is a rarer form of HUS , called atypical, which is not associated with E.Coli O157 infection. Atypical HUS (aHUS) has two variants, sporadic and familial. The sporadic form occurs often without any preceding illness but can be associated with use of certain drugs (most notably the oral contraceptive), pregnancy and HIV infection. Recovery of kidney function is less common and many patients require long term dialysis. In the familial form several members of a family will, over a period of time, be affected in a way similar to the sporadic form.
We have found abnormalities in the genes for four proteins, called factor H, membrane cofactor protein, factor I and C3 in approximately 50% of aHUS. These all belong to a common group of proteins, named complement. They have an important role in allowing the body to differentiate between its own and foreign cells. If any of these genes is faulty then the body?s own cells can be damaged by mechanisms designed to destroy foreign cells.
There is evidence that in a small number of patients with aHUS that there are faults in more than one of these genes. We have DNA samples from nearly 250 patients with aHUS and wish to screen all the known genes even in those patients in whom we have already found one fault.
We have recently found that the structure of the chromosome on which these genes lies is in some individuals with aHUS rearranged to form new genes, the presence of which predispose to the disease. We have also found that such rearrangements can lead to loss of genes and that this can predispose to another more common disease called age related macular degeneration. This is the commonest form of blindness in the elderly and has been shown to be associated with the factor H gene. We now wish to determine what the biological effect of loss of these genes is and whether it is more common with increasing age.
Technical Summary
It is now well established that the complement pathway is associated with both atypical haemolytic uraemic syndrome (aHUS) and age related macular degeneration (AMD). It has been shown that both mutations and susceptibility factors (SNPs and copy number variability) in complement genes including factor H, membrane cofactor protein, factor I, factor B and C3 predispose to aHUS. There is evidence to suggest that multiple such factors in individual patients can act in a summative manner to increase the risk of disease development. In the Newcastle cohort of 246 aHUS patients we will use a systems biology approach to model these multiple factors. Mutation screening, genotyping and dosage analysis will be undertaken to provide a complete profile of all these factors in the entire cohort. We will in the cohort also undertake mutation screening of other potential candidate genes including CD59, CR1 and properdin. We recently showed that a hybrid factor H/factor H related protein 1 gene formed by non-allelic homologous recombination (NAHR) was associated with aHUS. In this application we will confirm the presence of the reverse factor H related protein 1/factor H hybrid gene in association with aHUS using cDNA analysis and southern blotting. We have also shown that NAHR results in deletion of the genes encoding factor H related proteins 1 and 3 (CFHR1 and CFHR3), and that this deletion protects against the development of AMD but predisposes to aHUS. We will examine in normal subjects whether copy number of CFHR1 and CFHR3 is associated with serum levels of the proteins encoded by these genes and serum levels of factor H. To do this we will develop an ELISA for CFHR1 and CFHR3. In our studies examining copy number of CFHR1 and CFHR3 in aHUS and AMD we have observed that in control groups that the allele frequency of the deletion increases with ageing. We will examine the hypothesis that cumulative survival in the general population is associated with this deletion by examining the allele frequency in 4 independent cohorts of normal controls.
