Subtelomeric deletions of 1q43q44 and severe brain impairment associated with delayed myelination.

Subtelomeric deletions of 1q44 cause mental retardation, developmental delay and brain anomalies, including abnormalities of the corpus callosum (ACC) and microcephaly in most patients. We report the cases of six patients with 1q44 deletions; two patients with interstitial deletions of 1q44; and four patients with terminal deletions of 1q. One of the patients showed an unbalanced translocation between chromosome 5. All the deletion regions overlapped with previously reported critical regions for ACC, microcephaly and seizures, indicating the recurrent nature of the core phenotypic features of 1q44 deletions. The four patients with terminal deletions of 1q exhibited severe volume loss in the brain as compared with patients who harbored interstitial deletions of 1q44. This indicated that telomeric regions have a role in severe volume loss of the brain. In addition, two patients with terminal deletions of 1q43, beyond the critical region for 1q44 deletion syndrome exhibited delayed myelination. As the deletion regions identified in these patients extended toward centromere, we conclude that the genes responsible for delayed myelination may be located in the neighboring region of 1q43.