A 2 base "TA" deletion at positions 62 and 63 of an 83 base pair exon near the 5' end of the gene is found in the following mouse strains: A/HeJ, A/J, AKR/J, DBA/2J, I/LnJ, KK/HlJ, MOLF/EiJ, NZB/B1NJ, RF/J, ST/bJ SWR/J, B10.D2/oSnJ. The consequence of this deletion is the creation of a stop codon starting four bases after the deletion. A truncated product of 216 amino acids is predicted as a result although contradictory reports exist that a larger pro-C5 protein may be synthesized. Nevertheless, macrophages from mouse strains carrying this allele do not secrete complement 5.