Figure 1 Duplication and deletion syndromes. (A) The mechanism of non‐allelic homologous recombination between two chromosomes resulting in unequal meiotic exchanges. Circle: centromere; rectangle: low‐copy DNA repeat. (B–E) Subtle, but recognisable dysmorphic facial features in patients with 22q11 duplication syndrome (B), 22q11 deletion syndrome (C), Smith–Magenis syndrome (17p11.2 deletion; D) and Williams–Beuren syndrome (7q11.23 deletion; E). Parental/guardian informed consent was obtained for the publication of these figures.