To date, over 80 WRN disease mutations have been reported
from around the world [5,18–20]. These mutations were found
across the entire WRN gene, and include: (a) nonsense mutations
that change an amino acid codon to a stop codon and cause the
termination of protein translation; (b) insertions and/or deletions
(indels), which lead to reading frameshifts and subsequent termination
of protein translation; (c) substitutions at splice junctions
that cause the skipping of exons and a subsequent frameshift; (d)
missense mutations that cause amino acid changes in the protein;
(e) genomic rearrangements spanning multiple exons and
introns [18]. Most of the patient mutations result in truncations
of the WRN protein, eliminating the C-terminal nuclear localization
signal (NLS) [21]. This renders the protein unable to enter
the nucleus, making it functionally null. In addition, most of the
small indels and splicing mutations identified in WS are expected