Untangling the phenotypic heterogeneity of Diamond Blackfan anemia - PubMed (original) (raw)

Review

Untangling the phenotypic heterogeneity of Diamond Blackfan anemia

Jason E Farrar et al. Semin Hematol. 2011 Apr.

Abstract

Diamond Blackfan anemia (DBA) is a lineage-selective inherited bone marrow failure syndrome characterized primarily by anemia and physical malformations. Recent advances in identifying the genetic abnormalities underlying DBA have demonstrated involvement of genes encoding both large (RPL) and small (RPS) ribosomal subunit proteins, including mutations of RPL5, RPL11, RPL35A, RPS7, RPS10, RPS17, RPS19, RPS24, and RPS26 in 50% to 60% of affected patients. Despite significant progress, identification of gene abnormalities in the remaining patients remains an important question since present data suggest that mutations in other members of the ribosomal protein gene complement do not explain those cases without an identified genetic lesion in these genes. Genetic studies have also raised new questions with the recognition of substantial variability in the manifestations of DBA, ranging from ribosomal protein mutations in otherwise asymptomatic individuals to those with classic severe red blood cell aplasia with characteristic malformations, at times within the same kindred. In this review, we summarize the genetic basis of DBA and discuss mechanisms by which the phenotype of DBA might be modified.

Copyright © 2011 Elsevier Inc. All rights reserved.

PubMed Disclaimer

Figures

Figure 1

Figure 1. Examples of phenotypic variability in DBA families with r-protein mutations

Variability in clinical expression of shared r-protein gene muations in a) RPS19, b) RPS24, c) RPL35A, and d) RPL11. The patient designation in the primary reference is indicated in parentheses. Open symbols represent phenotype- and genotype- normal individuals (W) or phenotypically normal without reported genotype data (?). Filled symbols represent affected individuals with classic DBA findings including anemia requiring transfusion or steroid therapy with or without malformation. Graded symbols represent non-classical or incomplete DBA phenotype sharing an r-protein mutation with family members. Symbol codes: A: anemia (−: none, o: only laboratory abnormalities, +: requiring treatment) M: malformation (−: none, ?: not reported, +: present). Subscript below symbols represents multiple individuals.

Figure 2

Figure 2. Quantitative RT-PCR analysis of RPS19 on a panel of tissues and cell lines

Quantitative RT-PCR of RPS19 mRNA corresponding to nucleotide −3 to +89 was performed in triplicate and normalized to β-actin. The mean RPS19 expression is related to β-actin expression.

Figure 3

Figure 3. Structural variants in the 5’UTR of RPS19 cause reduced protein levels

Three DBA associated 5’UTR variants (c.-147_-146insGCCA, c.-147_-146insAGCC and c.- 144_-141delTTTC), were generated by site directed mutagenesis and transiently expressed in HEK293T or K562 cells from plasmid containing the complete coding sequence of RPS19 and 382 nucleotides of wild-type or variant 5’UTR. Transient expression demonstrates significantly reduced (20–30%) RPS19 protein levels for all three variants when compared to the wild-type construct (p < 0.05). Transfections were performed in triplicates and analyzed by Western blot normalized to beta-actin.

Figure 4

Figure 4. Alternative splicing of RPL35A mRNA resulting in a truncated protein caused by nucleotide substitution

Two RPL35A RNA products were amplified from the proband using RT-PCR with primers designed to amplify the full-length RPL35A message. A shorter product resulting from an alternative splicing event between exons 3 and 4 was identified along with normally-spliced mRNA containing both alleles. The arrows above the transcript diagram show the normal splicing event leading to wild-type RPL35A; sequence indicating the mutation position is shown above the schematic exon 3, with non-reference base shown in gray. The arrows below exon 3 demonstrate the abnormal splicing event resulting from activation of a cryptic splice donor site within exon 3 immediately upstream of the mutation, causing removal of 70 base pairs of 3' exon 3 coding sequence in addition to the intron. The amino acid sequence of wild-type, simple amino-acid substitution, and the splicing variant are shown below.

References

    1. Gustavsson P, Skeppner G, Johansson B, Berg T, Gordon L, Kreuger A, et al. Diamond-Blackfan anaemia in a girl with a de novo balanced reciprocal X;19 translocation. J Med Genet. 1997;34:779–782. - PMC - PubMed
    1. Gustavsson P, Willing TN, van Haeringen A, Tchernia G, Dianzani I, Donner M, et al. Diamond-Blackfan anaemia: genetic homogeneity for a gene on chromosome 19q13 restricted to 1.8 Mb. Nat Genet. 1997;16:368–371. - PubMed
    1. Gustavsson P, Garelli E, Draptchinskaia N, Ball S, Willig TN, Tentler D, et al. Identification of microdeletions spanning the Diamond-Blackfan anemia locus on 19q13 and evidence for genetic heterogeneity. Am J Hum Genet. 1998;63:1388–1395. - PMC - PubMed
    1. Draptchinskaia N, Gustavsson P, Andersson B, Pettersson M, Willig TN, Dianzani I, et al. The gene encoding ribosomal protein S19 is mutated in Diamond-Blackfan anaemia. Nat Genet. 1999;21:169–175. - PubMed
    1. Matsson H, Klar J, Draptchinskaia N, Gustavsson P, Carlsson B, Bowers D, et al. Truncating ribosomal protein S19 mutations and variable clinical expression in Diamond-Blackfan anemia. Hum Genet. 1999;105:496–500. - PubMed

Publication types

MeSH terms

Substances

Grants and funding

LinkOut - more resources