Structural variation in the alleles of a short tandem repeat system at the human alpha fibrinogen locus

This paper reports the sequences of 22 alleles identified at the HumFGA (human alpha fibrinogen) short tandem repeat locus in the British Caucasian and Afro-Caribbean populations. Alleles at the lower end of the observed size range were found to increase in size by 4-bp increments with the repeat unit following the pattern TC(TCTT)(n). However, 5 alleles were identified that differed in size by 2 bp from the 4 bp increment as a result of the deletion of a TC dinucleotide, or the addition of a TT dinucleotide, immediately prior to the Ist repeat unit. Alleles at the upper end of the observed size range were found to have a more complex repeat unit structure and also exhibited duplication of both 5' and 3' flanking sequences. A nomenclature for the designation of HumFGA alleles is proposed on the basis of this sequence data.