Identification of a new in-frame deletion of six amino acids in ribosomal protein S19 in a patient with Diamond-Blackfan anemia

A new in-frame deletion in ribosomal protein S19 in a Chinese infant with Diamond-Blackfan anemia

Diamond-Blackfan anemia (DBA) is a congenital erythroid aplasia that usually presents as macrocytic anemia during infancy. Ribosomal protein S19 (RPS19) is identified as the first gene associated with DBA. RPS19 is mutated in 25% of DBA patients, but its role in DBA pathogenesis remains to be elucidated. We have identified a novel heterozygous frameshift mutation in RPS19 gene in a DBA child presenting with profound anemia after birth. A single nucleotide heterozygous deletion (C.251delG) results in frameshift in RPS19 gene in exon 4 at codon 84 with possible premature stop codon (p.Arg84LysfsX21). The mutant allele was not detected in her parents, indicating de novo mutation. Both alleles were expressed at the same level. Using an immunofluorescence technique, the mutated-type RPS19 expressions were mostly localized to entire nuclei with little staining for nucleoli and its intracellular localization significantly differed from the wild-type RPS19, which was localized to both nuclei and nucleoli. This type of a mutation could be very helpful in further understanding the role of the RPS19 protein 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.

Ribosomal protein S17 gene (RPS17) is mutated in Diamond-Blackfan anemia

Diamond-Blackfan anemia (DBA) is a congenital erythroid aplasia characterized as a normochromic macrocytic anemia with a selective deficiency in red blood cell precursors in otherwise normocellular bone marrow. In 40% of DBA patients, various physical anomalies are also present. Currently two genes are associated with the DBA phenotype--the ribosomal protein (RP) S19 mutated in 25% of DBA patients and RPS24 mutated in approximately 1.4% of DBA patients. Here we report the identification of a mutation in yet another ribosomal protein, RPS17. The mutation affects the translation initiation start codon, changing T to G (c.2T>G), thus eliminating the natural start of RPS17 protein biosynthesis. RNA analysis revealed that the mutated allele was expressed, and the next downstream start codon located at position +158 should give rise to a short peptide of only four amino acids (Met-Ser-Arg-Ile). The mutation arose de novo, since all healthy family members carry the wild-type alleles. The identification of a mutation in the third RP of the small ribosomal subunit in DBA patients further supports the theory that impaired translation may be the main cause of DBA pathogenesis.