The Manton Center for Orphan Disease Research
Hanna T. Gazda, MD, PhD
Dr. Gazda's research focuses on identifying the genetic causes and molecular pathogenesis of Diamond-Blackfan anemia (DBA), a bone marrow failure characterized by anemia, bone marrow erythroblastopenia and congenital abnormalities. The first DBA gene, ribosomal protein S19, was found to be mutated in ~25% of DBA patients. Gazda and colleagues recently identified four other genes, RPS24, RPL5, RPL11, and RPS7, mutated in ~15% of DBA patients, and confirmed that DBA is a first human disease caused by mutations in ribosomal proteins. They also discovered the first known correlation between mutations in certain genes and particular clinical findings. In particular, mutations in RPL5 are associated with multiple physical abnormalities including cleft lip/cleft palate, thumbs and heart anomalies, while isolated thumb malformations are predominantly present in patients carrying mutations in RPL11. The laboratory's current goal is to identify other genes involved in DBA, to uncover the pathogenesis of the disease and to generate an animal model for DBA.
Genetics and Biology of Ribosomes in Diamond-Blackfan Anemia
Diamond-Blackfan anemia (DBA) is the first human disease known to be caused by mutations in ribosomal protein (RP) genes. Ribosomal protein genes provide the information for our body to produce ribosomal proteins. There are 79 ribosomal proteins, which together with ribosomal RNA form ribosomes. There are seven RP genes reported to be mutated in ~ 42% of DBA patients. Recently, we have completed screening by sequencing of the all 79 RP genes (excluding one gene, RPS4Y, located on chromosome Y) and have obtained evidence for mutations in four additional RP genes in ~10% of DBA patients. This brings the total number of RP genes mutated in ~52% of patients with DBA to 11.
The fact that several RP genes are mutated in DBA leads us to hypothesis that DBA is the ribosomal disease and that may be other mutations such as bigger deletions (missing pieces of DNA) or duplications (extra pieces of DNA) in RP genes which we were not able to find by sequencing as it detects only small deletions or insertions. We also hypothesize that other genes, which give information to produce proteins necessary for assembly of ribosomes may be mutated in DBA. Therefore, we propose: 1) to screen the DNA from patients with DBA for deletions and duplications in RP genes and in genes important for ribosomal assembly using technology called comparative genomic hybridization, 2) to sequence ~110 genes important for ribosomal assembly.
Because the mutations in RP genes cause abnormal maturation of ribosomal pre-RNA we hypothesize that mutations including bigger deletions and duplications in RP genes or the genes important for ribosomal assembly may also cause abnormal maturation of ribosomal pre-RNA and in consequence abnormal ribosomal assembly. We propose to test this hypothesis by performing experiments called Northern blot, which shows the pattern of pre-RNA maturation. Moreover, we believe we will be able to develop the pre-RNA maturation assay to confirm the mutations in the newly discovered genes.