AB001

Diamond-Blackfan anemia (DBA) is a congenital disorder that results predominantly from mutations in various ribosomal protein genes. In order to determine how these mutations affect the translation of specific mRNAs, we performed microarray analysis of polysomal transcripts isolated from lymphoblast cells derived from DBA patients carrying different haploinsufficient mutations in either RPS19 or RPL11. One of the few overlapping transcripts that we found significantly decreased on the polysomes codes for branched-chain aminotransferase-1 (BCAT-1). We go on to determine that translation of BCAT-1 is especially impaired in cells carrying mutations in the small ribosomal protein genes, and provide evidence that this effect is due to its unusually long 5’UTR. The BCAT-1 enzyme is critical for synthesis of the branched-chain amino acids, including leucine. It is known that DBA patients respond well to orally administered leucine, and large-scale clinical trials as such are currently underway. Our results suggest that the haploinsufficient loss of ribosomal protein genes results in a decrease of BCAT-1 translation and provide an explanation for why leucine administration is beneficial for DBA patients. In this expression study duplicate mRNA samples were generated from polysomes isolated from celllines with mutations in RPS19 or RPL11 or normal controls. In each group 3 cellines were tested. Duplicate samples were analyzed in dyeswap. As common reference the commercial universal human reference RNA (Stratagene) was used.