AN UNUSUAL COMBINED INSERTION DELETION POLYMORPHISM IN INTRON-10 OF THE HUMAN-COMPLEMENT C6 GENE/

Investigation of intron 10 of the human complement C6 gene revealed an unusual combined insertion/deletion polymorphism at position 493: the subsequent 6 bp is deleted and is substituted by a different 26 bp. g iving a net gain of 20 bp. The variant shows autosomal co-dominant inh eritance. The 26 bp insertion is homologous to a human endogenous retr ovirus-type sequence and could tentatively be ascribed to a retroposon . Alternatively, the presence of three copies of a 5 bp direct repeat, an 8 bp palindrome and a 12 bp split symmetrical element could sugges t an endogenous, sequence-mediated mutational process. Polymorphisms o f this type are extremely rare, although there are several examples of such mutations causing disease.