RP1 and retinitis pigmentosa 1: Our previous studies on lymphoblasts of patients with RP1 disease and gene targeted Rp1-tm1EAP mice suggest that the mutant RP1 mRNAs with nonsense mutations in exon 4 are expected to escape NMD, but the hypothesis that premature termination codons in exon 4 lead to the production of truncated Rp1 proteins in vivo has not been tested empirically with a representative mutant allele [37].