Investigation of rare genetic causes in diamond-blackfan anemia patients with unknown etiology

Diamond-Blackfan Anemia (DBA) is an inherited bone marrow failure syndrome (IBMFS) characterized by early-onset anemia and congenital malformations. DBA is also classified as a ribosomopathy, as the most frequently (%25) affected gene is RPS19, encoding a ribosomal protein (RP). Although rare autosomal recessive causes beside RPs (ADA2, HEATR3) have been described in recent years, the genetic etiology cannot be elucidated in ~20% of individuals, even in well-studied DBA cohorts. In this thesis, 30 affected individuals from Turkey who were referred with a suspected diagnosis of DBA has been examined to elucidate the unresolved genetic etiology. These affected individuals were first evaluated for disease-causing RPS19 or ADA2 variants, then copy number variations were examined by microarray and finally whole exome sequencing (WES) analysis was performed. As a result, pathogenic variants were found in DBA-related RP genes (RPS19, RPL5, RPS29, RPS26, RPS24, RPL35A) in 12 (40%) of the 30 affected individuals and biallelic ADA2 mutations were detected in 3 (10%) affected individuals. In the thesis cohort, the diagnostic rate was 70%, including 6 (20%) individuals with a pathogenic variant in a non-DBA gene whose etiology was clarified. Among individuals with DBA-related variants, a de novo duplication containing RPL5 was observed and, for the first time, a RP gene duplication has been associated with DBA. Additionally, in a family with 2 affected individuals a rare variant in RPS29 gene was found to segregate with the DBA phenotype consistent with an autosomal recessive inheritance pattern, unveiling autosomal recessive inheritance as a possible mechanism in RP-related DBA. Furthermore, a rare de novo heterozygous frameshift mutation in a protein-coding gene involved in the transport of snoRNAs was demonstrated in an affected individual, and a potential candidate gene for DBA was identified. In addition, genotype-phenotype correlations within the Hacettepe DBA Cohort was explored, and the phenotypic differences between individuals with pathogenic ADA2 variants and individuals with classical DBA has been demonstrated for the first time. In conclusion, in this thesis, the genetic causes of DBA in Turkey has been investigated in a large cohort, shedding light on the etiology of DBA by uncovering new mechanisms in known RPs and discovering a novel gene candidate.