Figure 2.
Schematic representation of the proposed recombination events leading to the variety of small microduplications involving CHRNA7. CHRNA7-LCRs are depicted in red. The yellow rectangle represents the ~90-kb segment in BP4 that is duplicated in patients with small microdeletion and deleted in patients with reciprocal microduplication (class 1 or 3). A, B: The most common class 1/1* microduplication is shown. A: Class 1 microduplication with inversion breakpoints mapping within the A segment of BP4 and BP5 (brackets), but further downstream of CHRFAM7A and CHRNA7, respectively. NAHR between proximal and distal CHRNA7-LCRs leads to the loss of a copy of the BP4B repeat. B: Class 1* microduplication with inversion breakpoints (vertical dashed lines) mapping in intron 4 of CHRNA7 and its homologous part of CHRFAM7A within the A portion of BP5 and BP4, respectively. Note that the entire true copy of CHRNA7 is duplicated in A and C, and the fusion of the upstream portion of the true copy of CHRNA7 (exons 1–4) with the downstream portion of the CHRFAM7A gene (homologous to exons 5–10 of CHRNA7) is generated due to BP4–BP5 inversion. C: Class 3 of the small microduplications is depicted. NAHR between proximal and distal CHRNA7-LCRs leads to the duplication of the A repeat of BP5.