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FISH validation of the GRM5 CNV. Metaphase spreads from (a) the non-affected father and (b) an ADHD patient with the deletion hybridized with probes labeled with Spectrum red (red signal) or Spectrum green (green signal). FISH was performed using fosmid W12-2219g4 (red signal) specific for the GRM5 deletion and BAC RP11-697e14, a control probe for the subtelomeric region of chromosome 11q (green signal). A portion of the GRM5 gene, including the 82kb region deleted in this family, is part of a 325kb segmental duplication present in two copies on chromosome 11, one in 11q and the other in 11p. This results in the observation of two red signals for the GRM5 probe in the non-deleted father (a), on both homologs of chromosome 11 indicated by white arrowheads. The annotated GRM5 gene in the reference genome is present on 11q. In the deleted patient (b), the red signal on 11q is missing on one of the two chromosome 11 homologs, because of the deletion within the GRM5 gene, (indicated by a blue arrowhead).