2q23.1 microdeletion syndrome is a recently characterized chromosomal aberration disorder uncovered through array comparative genomic hybridization (array CGH). Although the cardinal feature is intellectual disability (ID), neurodevelopmental features of the syndrome have not been systematically reviewed. We present a 5-year-old boy with severe psychomotor developmental delay/ID, progressive microcephaly with brain atrophy, growth retardation, and several external anomalies. He manifested intractable epilepsy, effectively treated with combined antiepileptic drug therapy including topiramate. Array CGH demonstrated a de novo interstitial deletion of approximately 1 Mb at 2q23.1-q23.2, involving four genes including MBD5. Nineteen patients have been reported to have the syndrome, including present patient. All patients whose data were available had ID, 17 patients (89%) had seizures, and microcephaly was evident in 9 of 18 patients (50%). Deletion sizes ranged from 200 kb to 5.5 Mb, comprising 1-15 genes. MBD5, the only gene deleted in all patients, is considered to be responsible for ID and epilepsy. Furthermore, the deletion junction was sequenced for the first time in a patient with the syndrome; and homology of three nucleotides, identified at the distal and proximal breakpoints, suggested that the deletion might have been mediated by recently-delineated genomic rearrangement mechanism Fork Stalling and Template Switching (FoSTeS)/microhomology-mediated break-induced replication (MMBIR).
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