High Frequency of RPL11 Gene Mutation in Italian Patients with Diamond-Blackfan Anemia

Diamond Blackfan anemia (DBA, MIM#205900) is a rare, pure red blood cell aplasia of childhood due to an intrinsic defect in erythropoietic progenitors. About 40% of cases show malformations. Anemia is corrected by steroid treatment in half of the patients; non-responders need chronic transfusions or stem cell transplantation.

Defects in the RPS19 gene, encoding the ribosomal protein (RP) S19, are the main known cause of DBA and account for more than 25% of patients. Mutations in other RPs (RPS24, RPS17, RPL35a) have been reported in a minority of patients (Gazda et al., 2006; Cmejla et al., 2007; Farrar et al., 2008) and show that DBA is a disorder of ribosome synthesis. Recently, Gadza et al. (2007) reported the involvement of two new genes (RPL5, RPL11) encoding for RPs of the large subunit in a considerable percentage of DBA patients without mutations in RPS19 or RPS24 (10% and 6,5%, respectively).

Here we present the results of RPL11 mutation screening in Italian DBA patients without RPS19 or RPS24 mutations. Preliminary data of RPL5 analysis are also reported.

The human RPL11 gene includes 6 exons and spans 4622 bp on chromosome 1. We identified 12 heterozygous mutations in 80 analyzed probands (15%), 10 of which were deletions of 1–47 nucleotides causing frameshift and a premature termination; another deletion (12nt) resulted in a loss of 4 aminoacids. One acceptor splice site defect (intron 5) was also detected. RPL11 mutations were spread in all exons except for exon 1.

The human RPL5 gene spans 9888 bp on chromosome 1, and includes 8 exons. We identified one heterozygous mutation in RPL5 in 14 analyzed patients (7%); it is a single nucleotide deletion in exon 5 causing frameshift and a premature termination.

None of these sequence changes were found on the NCBI SNP dalabase (http://www.ncbi.nlm.nih.gov/SNP/).

Our mutations are expected to alter the genetic information drastically and to cause haploinsufficency. Depletion of RPs compromises ribosome biogenesis and disturbs rRNA processing at different levels (Robledo et al. 2008).

Interestingly, all mutated patients (11/13) showed one or more somatic malformations; specifically, thumb anomalies and growth retardation were present in 7/11 (64%) and 6/11 (54%) patients, respectively. The erythrocyte adenosine deaminase activity was performed in 6/13 mutated patients; all of them showed an increased activity. The majority of RPL11 mutated patients were transfusion-dependent at last follow-up (58%,7/12); the RPL5 mutated patient was in clinical remission after steroid treatment. No one of the mutated patients has so far developed neoplasia.

Our data show that RPL11 mutations are more frequent than expected (Gazda et al. 2007). They seem to confer a relevant association with a malformation phenotype as compared to RPS19 mutations.