Nonallelic homologous recombination (NAHR)

(A) Balanced recombination (normal process) – The round circles labeled A and B represent LCRs, defined as repetitive DNA sequences >10 kb in size with 97% sequence identity. LCRs are located in the same chromosomes and arranged directly oriented and separated 5 Mb from each other. Recombination will proceed correctly and cause genetic information, A and B (blue rectangles), to swap places (ie, move to opposite DNA strands).
(B) Meiotic error – A and B, representing LCRs with similar homology, pair erroneously and lead to duplicated material on the upper strand and deleted material on the lower strand.
(C) Abnormal PMP22 recombination – Aberrant recombination, resulting in an imbalanced swap of DNA leading to PMP22 duplication, cause Charcot-Marie-Tooth disease. Aberrant recombination leading to deletions of PMP22 cause hereditary neuropathy with liability to pressure palsies (HNPP, tomaculous neuropathy).