Characterization of an isoelectric focusing variant of SAA1 (ASP-72) in a family of Turkish origin.

An acidic variant of serum amyloid A (SAA) identified previously by isoelectrofocusing in a family of Turkish origin has been characterized at the genomic level. DNA sequence analysis revealed that individuals expressing the variant pI6.1/pI5.7 isoforms (the mother and three of four children) were heterozygous at the SAA1 gene locus. Their SAA1 gene sequences contained an adenine, as well as the usual guanine, at the position corresponding to the second base of codon 72. The presence of both bases predicts two SAA1 protein sequences, one having aspartic acid and the other glycine at position 72. While the Gly-72 SAA1 (+/- Arg-1) sequence represents the normal pI6.5/pI6.0 isoforms, the Asp-72 SAA1 (+/- Arg-1) sequence corresponds to the variant pI6.1/pI5.7 isoforms.