FRAS1 and Down syndrome: We carried out an embryonic lethal screen to identify recessive mutations causing birth defects and identified a strain with a classic blebs phenotype and mutation in the Fraser syndrome gene Fras1. Disease causing mutations in FRAS1 do not appear to be clustered within any particular region of the gene and can be found scattered throughout the open reading frame, although more than half of these are nonsense mutations (Figure 2C) [21], [22], [23], [24], [25], [26], [27].