Abstract 2722: Large Scale Mutation Discovery Screen Identifies Functionally Variant UGDH Alleles in Patients with Atrioventricular Valve Defects
Background: Congenital heart defects are the most common birth defects. Although genetic dispositions are believed to cause CHDs, only few genes have been identified that harbour mutations causing such defects. Studies in model organisms have identified many essential genes for cardiac development. UDP-glucose dehydrogenase (UGDH) enzymatic activity is required for the signal transduction of FGF and Wnt ligands and zebrafish jekyll/ugdh mutations lack AV valves.
Methods and Results: From literature candidate genes were selected that are essential for AV canal-, septum-, and valve formation. By large scale sequencing we analysed the coding regions of 36 candidate genes in 192 patients with reported AVSDs. As a result we identified 457 genetic variations of which 207 variants are in flanking non-coding regions, 156 variants are in coding regions but silent and 94 variants are non-synonymous variants that alter the protein sequence. Comparison with the available databases such as HapMap and screening 350 control individuals resulted in the validation of 49 non-synonomous missense mutations in 23 genes only present in the patient group. These included novel GATA4 missense mutations (R285C and M224V) located in the highly conserved DNA binding domains, which by in vitro analysis significantly reduce transcriptional activity of the protein. Three patients with mitral valvar prolapse and mitral regurgitation were identified with novel missense mutations in the UDP-glucose dehydrogenase (UGDH) gene (R141C and E416D). In vitro experiments demonstrated a negative affect on enzyme activity and stability by a change in protein conformation. Furthermore, experiments in zebrafish jekyll/ugdh mutants showed that UGDH R141C and UGDH E416D couldn’t rescue the defects in AV formation demonstrating an inactivating effect of these missense mutations in vivo.
Conclusions: A model organism based candidate gene screen in CHD patients resulted in the identification of novel functional missense mutations in the UGDH gene not previously implicated in congenital heart defects.