A de novo 22q11.22q11.23 interchromosomal tandem duplication in a boy with developmental delay, hyperactivity, and epilepsy.

The recent development of high-throughput analysis for genomic copy numbers has enabled to identify microscopic chromosomal duplications that had never been recognized before. Microarray-based comparative genomic hybridization (aCGH) identified a de novo 2.1-Mb microduplication in the 22q11.22q11.23 region surrounded by low copy repeats (LCRs) LCR22E and LCR22H in a 5-year-old boy with developmental delay, hyperactivity, epilepsy, and distinctive facial features, which were within the wide range of the clinical manifestations of the patients with the same duplication pattern. Fiber-fluorescent in situ hybridization (FISH) analysis confirmed that the duplicated segments were aligned in a tandem configuration. Familial single nucleotide polymorphism (SNP) typing determined that the duplication was derived from paternal interchromosomal non-allelic homologous recombination (NAHR) during the first meiotic process of spermatogenesis. Although no patient with the deletions of the distal 22q11.2 has been reported as showing epilepsy, at least five patients including the presenting patient having the duplication between LCR22E and LCR22G showed epilepsy. Thus, the gain of the genomic copy number of this region may have epileptogenesis.