Analysis of Ribosomal Protein Genes Associated with Diamond Blackfan Anemia (DBA) In German DBA Patients and Their Relatives

Abstract 729

On behalf of the German DBA registry. The first two authors contributed equally.

Mutations of ribosomal protein (RP) genes cause diamond blackfan anemia (DBA), a congenital bone marrow failure syndrome characterized by erythroid failure associated with diverse malformations of multiple organ systems. Familial dominant inheritance has been established in at least one third of all cases. Some affected family members present only with history of transient anemia during childhood without additonal clinical abnormalities. Laboratory parameters supporting the diagnosis of DBA and pointing towards a non-penetrant carrier are macrocytosis, elevated hemoglobin F (HbF) and adenosine deaminase (ADA). The presence of a more severe disease phenotype in DBA offsprings affected by the disease raised the question of potential genetic anticipation. However, the insufficient longitudinal datasets, the non-prospective nature of investigations and other complex issues such as fecundity bias make it difficult to evaluate this problem in DBA patients. The purpose of the current study was to investigate the incidence of mutations in ribosomal protein genes in family members of DBA patients, irrespective of family history, specific symptoms or laboratory parameters.

Based on the results from the ongoing DBA re-sequencing study we determined the mutational status of German DBA patients for the following 12 RP genes: RPS7, RPS10, RPS17, RPS19, RPS24, RPS26, RPL5, RPL9, RPL11, RPL19, RPL26, RPL35a. Out of 179 index patients with DBA, 94 patients carried an exclusive mutation or deletion of the following 9 genes: RPS19, n=46 (25,7%); RPL5, n=15 (8,4%); RPS26, n=12 (6,7%); RPL11, n=8(4,5%), RPL35a, n=6 (3,4%), RPS17, n=3 (1,7%), RPS24, n=2 (1,1%), RPS10, n=1 (0,6%), RPS7, n=1 (0,6%). In two patients, large genomic deletions were discovered using Affymetrix 6.0 SNP-array karyotyping, which encompass RPL5 and both copies of RPS17, respectively. No aberrations were found in RPL9, RPL19 and RPL26. A total of 85 patients (47%) were negative for all 12 tested genes. In the next step, RP genes with nonsynonymous changes identified in index patients were interrogated in patients` relatives. The investigation of parent-offspring trios revealed de novo gene aberrations in 32/55 (58%) of families (RPS19, n=14; RPL5, n=8; RPS26, n=4; RPL11, n=3, RPL35a, n=2; RPS17, n=1). Maternal inheritance pattern was identified in a total of 17/55 families (RPS19, n=10; RPS24, n=2; RPL5, n=2; RPS10, n=1; RPS26, n=1; RPL11, n=1), whereas a paternal transmission of the mutation was observed in 6/55 families (RPS19, n=3; RPL5, n=1; RPL35a, n=1 and RPS26, n=1). Among parents with identified mutation, 43% were silent carriers (presenting with normal phenotype and no history of anemia). Strikingly, 4/10 silent carriers with mutation (RPS10 Lys24Arg; RPS26 Arg87X; RPS19 Val30SerfsX46; RPS19 Arg94X) had normal HbF and ADA values. Taken together, spontaneous remission and silent clinical phenotype accounted for 87% of parental cases with identified RP mutations as opposed to 24% of offsprings with respective RP mutations.

In summary, in German DBA cohort, RP genetic defects arise de novo at a frequency of 58% and are inherited over at least one generation in 42% of cases, with no significant clustering of RP gene mutations. Maternal inheritance pattern predominates at 74% of all inherited cases. The unequal cumulative frequency of spontaneous remission and silent phenotype among parental subjects versus offsprings with mutated RP genes might indicate increasing severity of the disease in each generation. This observation and the unexpectedly high frequency of silent carriers with normal HbF and ADA values warrants further studies with a large number of longitudinal datasets and known RP gene status.