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Complement component C6 and C7 haplotypes associated with deficiencies of C6
B A Fernie1, A Orren, R Würzner
1Molecular Immunopathology Unit, MRC Centre, Cambridge, U.K.
Annals of Human Genetics
|April 1, 1995
Summary
Researchers identified a common defective haplotype in South African C6-deficiency (C6*Q0) patients, explaining subtotal C6-deficiency (C6*SD) phenotypes. This C6 gene defect is not solely responsible for combined C6/C7 deficiencies.
Area of Science:
- Human Genetics
- Molecular Biology
- Immunology
Background:
- Complete C6-deficiency (C6*Q0) and subtotal C6-deficiency (C6*SD) are simple recessive traits.
- C6*SD can occur with subtotal C7 deficiency, affecting an adjacent gene locus.
- The C6 protein in C6*SD exhibits altered size and isoelectric properties, suggesting a specific molecular defect.
Purpose of the Study:
- To investigate the genetic basis of C6-deficiency and its association with C7 deficiency.
- To identify specific DNA markers and haplotypes linked to C6*Q0 and C6*SD phenotypes.
- To determine if the identified C6 gene defect explains combined C6/C7 deficiencies.
Main Methods:
- Analysis of seven DNA markers for the C6 and C7 genes.
- Haplotype analysis in patients with C6*Q0, C6*SD, and combined C6/C7 deficiencies, and their relatives.
- Comparison of molecular defects in individuals with different deficiency phenotypes.
Main Results:
- A common defective haplotype is prevalent in South African C6*Q0 patients.
- This specific C6 gene defect is common to both C6*SD traits.
- In some families, C6*SD shares a haplotype with combined deficiency, suggesting heterozygosity; in others, C7 is normally expressed, indicating the C6 defect alone doesn't cause C7 deficiency.
Conclusions:
- A specific C6 gene defect explains the C6*SD phenotype and is common in South African C6*Q0 patients.
- The C6 defect is insufficient to cause C7 deficiency in combined deficiency cases.
- The haplotype associated with combined deficiency is found in normal individuals and one case of complete C6 deficiency lacking the specific molecular defect.