Duplications and insertions

Pathological duplication mutations are observed in some
disorders. In Duchenne muscular dystrophy, 5–10% of
mutations are due to duplication of exons within the
dystrophin gene, and in Charcot–Marie–Tooth disease type 1a,
70% of mutations involve duplication of the entire PMP22
gene. In DMD the mutation acts by causing a shift in the
translation reading frame, and in CMT 1a by increasing the
amount of gene product produced. Insertions of foreign DNA
sequences into a gene also disrupt its function, as in
haemophilia A caused by insertion of LINE1 repetitive
sequences into the F8C gene.