Identical amyloid precursor proteins in two breeds of chickens which differ in susceptibility to develop amyloid arthropathy

Chickens (Gallus gallus domesticus) can suffer from AA amyloidosis featurin g the joints as major targets of amyloid accumulation. Analysis of post-mor tem recordings from commercial chickens revealed that amyloid arthropathy-f requency occurred in brown layer chickens, but never in white layers. The s uspected higher susceptibility of brown layers was confirmed experimentally by inducing amyloidosis with an arthropathic and amyloidogenic strain off. faecalis. Sequence analysis of cDNA coding for SAA, the amyloid precursor protein, revealed that the SAA proteins are identical in both breeds, altho ugh some nucleotide differences existed in the untranslated regions of the mRNAs. The chicken SAA gene was found to be a single copy gene which compri ses 4 exons. The first of these exons apparently occupies a conserved posit ion and is not translated. Investigation of the affected joints using in si tu hybridization demonstrated local SAA gene expression. It is concluded th at the likelihood of an E. faecalis induced arthritis to progress to amyloi dosis is breed-dependent, but is not a consequence of a more amyloidogenic SAA.