C9 Gene

The C9 gene (C9 stands for "Complement C9") is a protein coding gene located at chromosome 5p13.1. The C9 gene encodes the last component of the complement system. It is involved in the formation of the"Membrane Attack Complex" (MAC). The MAC -complex attaches to bacterial membranes and forms a pore that allows disruption of bacterial membrane organization.

Mutations in the -C9 gene cause a deficiency of the complement component C9 and thus lead to a dysfunction of the MAC complex .

Diseases associated with C9 include C9 deficiency (Complement Component 9 Deficiency; OMIM: 613825) and "age-related macular degeneration 15/ARMD15 (615591)".

C9 deficiency is associated with an increased risk of meningococcal infections (Nagata M et al. 1989). Ichikawa E et al. 2001) could assign a case of dermatomyositis to a mutation in the C9 gene.

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

• 5 individuals with C5 deficiency (609536)
• 6 individuals with C6 deficiency (612446)
• 17 individuals with C7 deficiency (610102)
• 5 individuals with C8 alpha/gamma deficiency (2/100,000)
• 439 individuals with C9 deficiency (613825).

1. Fukumori Y et al.(1998) Terminal complement component deficiencies in Japan. Exp. Clin. Immunogenet 15: 244-248.
2. Ichikawa E et al. (2001) Hereditary complement (C9) deficiency associated with dermatomyositis. Brit J Derm. 144: 1080-1083.
3. Nagata M et al. (1989) Inherited deficiency of ninth component of complement: an increased risk of meningococcal meningitis. J Pediat 114: 260-264.