A four base pair insertion in exon 1 of the RPS19 gene is a common polymorphism in African-Americans

A family with Hoyeraal-Hreidarsson syndrome and four variants in two genes of the telomerase core complex

We describe an African American family with Hoyeraal-Hreidarrson syndrome (HHS) in which 2 TERT mutations (causing P530L and A880T amino acid changes) and two in the DKC1 variants (G486R and A487A) were segregating. Both genes are associated with dyskeratosis congenita and HHS. It was important to determine the importance of these mutations in disease pathogenesis to counsel family members. From genetic analysis of family members, telomere length and X-inactivation studies we concluded that compound heterozygosity for the TERT mutations was the major cause of HHS and the DKC1 G486R variant is a rare African variant unlikely to cause disease.

Untangling the phenotypic heterogeneity of Diamond Blackfan anemia

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.

5'UTR variants of ribosomal protein S19 transcript determine translational efficiency: implications for Diamond-Blackfan anemia and tissue variability

Background

Diamond-Blackfan anemia (DBA) is a lineage specific and congenital erythroblastopenia. The disease is associated with mutations in genes encoding ribosomal proteins resulting in perturbed ribosomal subunit biosynthesis. The RPS19 gene is mutated in approximately 25% of DBA patients and a variety of coding mutations have been described, all presumably leading to haploinsufficiency. A subset of patients carries rare polymorphic sequence variants within the 5′untranslated region (5′UTR) of RPS19. The functional significance of these variants remains unclear.

Methodology/Principal Findings

We analyzed the distribution of transcriptional start sites (TSS) for RPS19 mRNAs in testis and K562 cells. Twenty-nine novel RPS19 transcripts were identified with different 5′UTR length. Quantification of expressed w.t. 5′UTR variants revealed that a short 5′UTR correlates with high levels of RPS19. The total levels of RPS19 transcripts showed a broad variation between tissues. We also expressed three polymorphic RPS19 5′UTR variants identified in DBA patients. The sequence variants include two insertions (c.-147_-146insGCCA and c.-147_-146insAGCC) and one deletion (c.-144_-141delTTTC). The three 5′UTR polymorphisms are associated with a 20–30% reduction in RPS19 protein levels when compared to the wild-type (w.t.) 5′UTR of corresponding length.

Conclusions

The RPS19 gene uses a broad range of TSS and a short 5′UTR is associated with increased levels of RPS19. Comparisons between tissues showed a broad variation in the total amount of RPS19 mRNA and in the distribution of TSS used. Furthermore, our results indicate that rare polymorphic 5′UTR variants reduce RPS19 protein levels with implications for Diamond-Blackfan anemia.

Genetic variants in the noncoding region of RPS19 gene in Diamond-Blackfan anemia: potential implications for phenotypic heterogeneity

Mutations in the RPS19 gene have been identified in 25% of individuals affected by Diamond-Blackfan anemia (DBA), a congenital erythroblastopenia characterized by an aregenerative anemia and a variety of malformations. More than 60 mutations in the five coding exons of RPS19 have been described to date. We previously reported a mutation (c.-1 + 26G>T) and an insertion at -631 upstream of ATG (c.-147_-146insGCCA) in the noncoding region. Because DBA phenotype is extremely heterogeneous from silent to severe and because haploinsufficiency seems to play a role in this process, it is likely that genetic variations in the noncoding regions affecting translation of RPS19 can modulate the phenotypic expression of DBA. However, to date, very few studies have addressed this question comprehensively. In this study, we performed detailed sequence analysis of the RPS19 gene in 239 patients with DBA and 110 of their relatives. We found that 6.2% of the patients with DBA carried allelic variations upstream of ATG: 3.3% with c.-1 + 26G>T; 2.5% with c.-147_-146insGCCA; and 0.4% with c.-174G>A. Interestingly, the c.-147_-146insGCCA, which has been found in a black American and French Caribbean control population, was not found in 500 Caucasian control chromosomes we studied. However, it was found in association with the same haplotype distribution of four intronic polymorphisms in our patients with DBA. Although a polymorphism, the frequency of this variant in the patients with DBA and its association with the same haplotype raises the possibility that this polymorphism and the other genetic variations in the noncoding region could play a role in DBA pathogenesis.

RPS19 mutations in patients with Diamond-Blackfan anemia

Diamond-Blackfan anemia (DBA) is an inherited disease characterized by pure erythroid aplasia. Thirty percent (30%) of patients display malformations, especially of the hands, face, heart, and urogenital tract. DBA has an autosomal dominant pattern of inheritance. De novo mutations are common and familial cases display wide clinical heterogeneity. Twenty-five percent (25%) of patients carry a mutation in the ribosomal protein (RP) S19 gene, whereas mutations in RPS24, RPS17, RPL35A, RPL11, and RPL5 are rare. These genes encode for structural proteins of the ribosome. A link between ribosomal functions and erythroid aplasia is apparent in DBA, but its etiology is not clear. Most authors agree that a defect in protein synthesis in a rapidly proliferating tissue, such as the erythroid bone marrow, may explain the defective erythropoiesis. A total of 77 RPS19 mutations have been described. Most are whole gene deletions, translocations, or truncating mutations (nonsense or frameshift), suggesting that haploinsufficiency is the basis of DBA pathology. A total of 22 missense mutations have also been described and several works have provided in vitro functional data for the mutant proteins. This review looks at the data on all these mutations, proposes a functional classification, and describes six new mutations. It is shown that patients with RPS19 mutations display a poorer response to steroids and a worse long-term prognosis compared to other DBA patients.