Biomedical subjects

Elizabeth J Kemp

Publications and source records attributed to Elizabeth J Kemp.

5 recordsLinked to original sources

PubMed2006

De novo gene conversion in the RCA gene cluster (1q32) causes mutations in complement factor H associated with atypical hemolytic uremic syndrome.

Many of the complement regulatory genes within the RCA cluster (1q32) have arisen through genomic duplication and the resulting high degree of sequence identity is likely to predispose to gene conversion events. The highest degree of identity is between the genes for factor H (CFH) and five factor H-related proteins--CFHL1, CFHL2, CFHL3, CFHL4, and CFHL5. CFH mutations are associated with atypical hemolytic uremic syndrome (aHUS). In the Newcastle cohort of 157 aHUS patients we have identified CFH mutations in 25 families or individuals. Eleven of these 25 independent mutations are either c.3226C>G,Q1076E; c.3572C>T,S1191L; c.3590T>C,V1197A or combined c.3572C>T,S1191L/c.3590T>C,V1197A. Sequence analysis shows that all four of these changes could have arisen as a result of gene conversion between CFH and CFHL1. Analysis of parental samples in two patients with S1191L/V1197A has shown that the changes are de novo thus providing conclusive evidence that gene conversion is the mutational mechanism in these two cases. To confirm that S1191L and V1197A are disease predisposing we examined their functional significance in three ways - analysis of the C3b/C3d binding characteristics of recombinant mutant S1191L/V1197A protein, heparin affinity chromatography and haemolytic assays of serum samples from aHUS patients carrying these changes. The results showed that these changes resulted in impaired C3b binding and a defective capacity to control complement activation on cellular surfaces. We, therefore, provide conclusive evidence that gene conversion is responsible for functionally significant CFH mutations in aHUS.

Animals↗

PubMed2005

Does complement factor B have a role in the pathogenesis of atypical HUS?

Atypical haemolytic uraemic syndrome (aHUS) is a disorder of complement dysregulation. Because complement factor B (fB) carries the catalytic site of the alternative pathway convertase we examined it as both a potential candidate gene and modifier in the pathogenesis of aHUS. No factor B gene (BF) mutations were found in 20 patients with aHUS. There was no statistical difference between controls and aHUS patients in either BF allele or haplotype frequency. In conclusion, in this small series of aHUS patients we found no evidence that fB has a major role in the pathogenesis of aHUS.

Case-Control Studies↗

PubMed2005

Mutations in complement factor I predispose to development of atypical hemolytic uremic syndrome.

Mutations in the plasma complement regulator factor H (CFH) and the transmembrane complement regulator membrane co-factor protein (MCP) have been shown to predispose to atypical hemolytic uremic syndrome (HUS). Both of these proteins act as co-factors for complement factor I (IF). IF is a highly specific serine protease that cleaves the alpha-chains of C3b and C4b and thus downregulates activation of both the classical and the alternative complement pathways. This study looked for IF mutations in a panel of 76 patients with HUS. Mutations were detected in two patients, both of whom had reduced serum IF levels. A heterozygous bp change, c.463 G>A, which results in a premature stop codon (W127X), was found in one, and in the other, a heterozygous single base pair deletion in exon 7 (del 922C) was detected. Both patients had a history of recurrent HUS after transplantation. This is in accordance with the high rate of recurrence in patients with CFH mutations. Patients who are reported to have mutations in MCP, by contrast, do not have recurrence after transplantation. As with CFH- and MCP-associated HUS, there was incomplete penetrance in the family of one of the affected individuals. This study provides further evidence that atypical HUS is a disease of complement dysregulation.

Adult↗

PubMed2004

Mutations in CD46, a complement regulatory protein, predispose to atypical HUS.

Membrane cofactor protein (MCP, CD46) is a widely expressed transmembrane complement regulator. As does the soluble regulator factor H, it inhibits complement activation by inactivating the C3b that is deposited on target membranes. Factor H mutations have been described in 15-30% of patients with atypical haemolytic uraemic syndrome (HUS). Recent studies have identified mutations in the MCP gene in four families. In one, a heterozygous deletion resulted in the intracellular retention of the mutant protein. In another, a different heterozygous deletion led to a premature stop codon and the loss of the C-terminus. In the other two, a substitution (S206P) resulted in cell-surface expression but inefficient inactivation of surface-bound C3b. These findings provide further evidence that complement dysregulation predisposes to the development of HUS.

Cell Membrane↗

PubMed2003

Mutations in human complement regulator, membrane cofactor protein (CD46), predispose to development of familial hemolytic uremic syndrome.

Membrane cofactor protein (MCP; CD46) is a widely expressed transmembrane complement regulator. Like factor H it inhibits complement activation by regulating C3b deposition on targets. Factor H mutations occur in 10-20% of patients with hemolytic uremic syndrome (HUS). We hypothesized that MCP mutations could predispose to HUS, and we sequenced MCP coding exons in affected individuals from 30 families. MCP mutations were detected in affected individuals of three families: a deletion of two amino acids (D237/S238) in family 1 (heterozygous) and a substitution, S206P, in families 2 (heterozygous) and 3 (homozygous). We evaluated protein expression and function in peripheral blood mononuclear cells from these individuals. An individual with the D237/S238 deletion had reduced MCP levels and approximately 50% C3b binding compared with normal controls. Individuals with the S206P change expressed normal quantities of protein, but demonstrated approximately 50% reduction in C3b binding in heterozygotes and complete lack of C3b binding in homozygotes. MCP expression and function was evaluated in transfectants reproducing these mutations. The deletion mutant was retained intracellularly. S206P protein was expressed on the cell surface but had a reduced ability to prevent complement activation, consistent with its reduced C3b binding and cofactor activity. This study presents further evidence that complement dysregulation predisposes to development of thrombotic microangiopathy and that screening patients for such defects could provide informed treatment strategies.

Amino Acid Substitution↗