Atypical Werner's Syndrome(WS) is a disease characterized with accelerated aging characterized by short stature, thinning/graying of hair, a "bird-like" facial appearance, skin atrophy and is caused by the mutation of the LMNA gene; by analysis of the Gene the researcher revealed a T deletion in exon 2 in the LMNA gene that resulted in altered amino acid sequence from codon 169 to stop codon. This type of mutations best describe as? ​