C6 deficiency, subtotal included D84.1

The very rare C6 deficiency (C6D) is caused by a homozygous or compound heterozygous mutation in the C6 gene (217050) on chromosome 5p13.

Fukumori Y et al (1998) identified in Japan by screening for complement deficiencies in 145,640 blood donors from Osaka and in 92. 686 donors from all of Japan:

• 5 individuals with C5 deficiency (609536) (2/100,000).
• 6 persons with C6 deficiency (2.4/100,000)
• 17 individuals with C7 deficiency (610102)
• 5 individuals with C8 alpha/gamma deficiency (613790) (2/100,000)
• 439 individuals with C9 deficiency (613825).

Both total C6 complement deficiency and subtotal C6 complement deficiency are described. Individuals with subtotal C6 deficiency have a C6 molecule that is 14% shorter than normal C6 and is present in low but detectable concentrations in serum (1 to 2% of normal average). Clinically, C6 deficiency is associated with severe bacterial (mainly N. meningitides) infections (Bae JY et al. 2020; Kernbaum S et al. 1980; Rauscher CK et al. 2020) as well as autoimmunological phenomena (arthritis, positive ANA, SLE-like symptoms) (Tedesco F et al. 1981).

1. Bae JY et al.(2020) Recurrent meningococcal meningitis with complement 6 (C6) deficiency: A case report. Medicine (Baltimore) 99: e20362.
2. Fukumori Y et al. (1998) Terminal complement component deficiencies in Japan. Exp. Clin. Immunogenet. 15: 244-248.
3. Kernbaum S et al (1980) Human deficiency of the sixth component of complement in a patient with meningococcal meningitis and no haemostasis abnormality. Biomedicine 33: 197-201.
4. Rauscher CK et al (2020) Clinical implications of C6 complement component deficiency. Allergy Asthma Proc 41:386-388.
5. Reinitz E et al (1986) Arthritis and antinuclear antibodies (ANA) with inherited deficiency of the sixth component of complement (C6). Ann Rheum Dis 45: 431-434.
6. Tedesco F et al (1981) A lupus-like syndrome in a patient with deficiency of the sixth component of complement. Arthritis Rheum 24: 1438-1440.
7. Vogler LB et al (1979) Recurrent meningococcal meningitis with absence of the sixth component of complement: an evaluation of underlying immunologic mechanism. Pediatrics 64: 465-467.