Complete deficiency of the sixth complement component (C6Q0), susceptibility to Neisseria meningitidis infections and analysis of the frequencies of C6Q0 gene defects in South Africans

Authors

  • A. Orren,

    1. Department of Infection, Immunity and Biochemistry, Cardiff University, Cardiff, UK
    2. Division of Chemical Pathology, Department of Clinical Laboratory Sciences, University of Cape Town
    3. Allergy Diagnostic and Clinical Research Unit, Department of Medicine, Lung Institute, University of Cape Town
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  • E. P. Owen,

    Corresponding author
    1. Division of Chemical Pathology, Department of Clinical Laboratory Sciences, University of Cape Town
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  • H. E. Henderson,

    1. Division of Chemical Pathology, Department of Clinical Laboratory Sciences, University of Cape Town
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  • L. van der Merwe,

    1. Department of Human Biology, University of Cape Town
    2. Biostatistics Unit, South African Medical Research Council
    3. Department of Statistics, University of Western Cape, Cape Town, South Africa
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  • F. Leisegang,

    1. Division of Chemical Pathology, Department of Clinical Laboratory Sciences, University of Cape Town
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  • C. Stassen,

    1. Allergy Diagnostic and Clinical Research Unit, Department of Medicine, Lung Institute, University of Cape Town
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  • P. C. Potter

    1. Allergy Diagnostic and Clinical Research Unit, Department of Medicine, Lung Institute, University of Cape Town
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  • Institution where the work was carried out: University of Cape Town Lung Institute, Allergy Diagnostic and Clinical Research Unit (ADCRU), and Department of Clinical Laboratory Sciences, University of Cape Town, PO Box 34560, Groote Schuur 7937, South Africa.

A. Orren, Department of Infection, Immunity and Biochemistry, School of Health Sciences, Cardiff CF14 4XN, UK. E-mail: orrena@cardiff.ac.uk

Summary

Complete complement component 6 deficiency (C6Q0) is a co-dominant genetic disease presenting as increased susceptibility to invasive Neisseria meningitidis infections. Affected individuals have two affected alleles which can be homozygous or compound heterozygous for the particular gene defects they carry. This disorder has been diagnosed relatively frequently in Western Cape South Africans. Affected patients are prescribed penicillin prophylaxis. In 2004 we commenced a clinical follow-up study of 46 patients. Of these, 43 had family age-matched C6 sufficient controls. Participants were classified as either (i) well, or (ii) having a serious illness (SI) or died (D). An SI was a long-term illness that did not allow the performance of normal daily activities. Among 43 patients, 21 were well and 22 were SI/D, while among 43 matched controls, 35 were well and eight were SI/D. This difference is highly significant. Among all 46 C6Q0 patients, those who had had recurrent infection had significantly more SI/D than those who had suffered none or one infection. Thus, this work demonstrates the long-term serious outcome of repeated meningococcal disease (MD) episodes. We investigated the frequencies of four C6Q0 pathogenic mutations known to affect Cape patients (828delG, 1138delC, 821delA and 1879delG) in 2250 newborns. A total of 103 defective alleles (2·28%) and three affected C6Q0 individuals were detected. For all defects combined, 5·24 affected subjects (C6Q0) are expected among 10 000 individuals. What is still unknown is the number of C6Q0 individuals who suffer MD or other infectious diseases.

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