A genetic marker for systemic amyloidosis in juvenile arthritis.

A genetic marker of susceptibility to systemic amyloidosis has been identified. A DNA polymorphic site, 5' to the serum amyloid P component gene, has been found to be significantly associated with amyloidosis in juvenile arthritic patients. When genomic DNA was cut with the restriction enzyme MspI and probed with the cDNA for serum amyloid P component, homozygosity for the 5.6 kb restriction fragment length polymorphic (RFLP) band was absent in all 28 amyloid patients. Furthermore, the proportion who were homozygous for the 8.8 kb RFLP band was greater (p = 0.008) than that among 89 normal subjects. The distribution of this polymorphic site among 19 juvenile arthritic patients without amyloidosis was the same as that in the normal group. Thus the 8.8 kb RFLP band represents a genetic predisposition to reactive amyloidosis in juvenile arthritis and may apply to amyloidosis associated with more common inflammatory conditions.