Bone Abstracts

Background: We discovered that variants in NBAS (Neuroblastoma Amplified Sequence Gene) known to be associated with acute liver failure are also responsible for skeletal abnormalities. This work was published as a novel cause of bone fragility [Balasubramanian et al., 2017]. NBAS role in bone fragility provides an opportunity to use tractable animal research to advance understanding of mechanism and identify potential new treatments. This would be beneficial to patients but also inform on a wider front regarding cell membrane trafficking and effect on collagen secretion.

Objectives: Hypotheses: - NBAS is required for cargo-selective, tissue-specific secretion/ glycosylation of collagen within cell; - Identifying druggable targets to rescue NBAS activity will reverse disease phenotype.

Methods: 1. In-depth analyses of skeletal manifestations and phenotype of homozygous mutant fish we have generated for a nonsense nbas allele. 2. Screening assays to rescue Nbas activity in mutant fish model to identify candidate small molecules.

Results: We decided to analyse an nbas mutant fish line, the predicted null mutation (sa16290) from EZRC stock center which have been grown up to adult fish. We have raised three generations of homozygous mutant fish to generate a mutant line that has a specific defect with Mendelian ratios, without any background mutations. The nbas mutant fish can be identified at between 4 and 5 days post fertilization (dpf), as they fail to inflate their swim bladder. We have analysed nbas mutants for skeletal manifestations and cartilage staining has revealed disorganised and rounded chondrocytes in the jaw. In comparison, wild-type embryos have chondrocytes that are uniform in size and stacked to form an organised structure. Day 5 Alcian Blue stain revealed chondrocytes neatly stacked in wildtype fish and more disorganised and rounded in homozygous nbas mutant fish. We are currently undertaking further studies to analyse in-depth nbas mutant fish and preliminary drug screening which will be presented.

Conclusion: Patients with NBAS mutations are subjected to lifetime of recurrent fractures, repeated episodes of acute liver failure needing recurrent hospital admissions and immune deficiency. Developing druggable targets towards making this condition better would have a positive impact on quality of life for patients.

Disclosure: The authors declared no competing interests.