Familial intellectual disability and autistic behavior caused by a small FMR2 gene deletion

Alterations of the Fragile Mental Retardation 2 gene (FMR2, synonym AFF2) can result in non-specific, mild to borderline X-linked intellectual disability (XLID), and behavioral problems. The well-known molecular pathomechanism of this condition, also referred to as FRAXE, is a (CCG)(n) trinucleotide repeat expansion which leads to silencing of the FMR2 gene. However, deletions within the FMR2 gene may also be causative of the disorder. Here, we report on two brothers diagnosed with FRAXE in whom a small deletion in the FMR2 gene was detected by whole genome array comparative genomic hybridization (CGH). The deletion was also present in their clinically healthy mother and maternal uncle who was similarly affected, but not in a healthy older brother of the two patients. Our observation demonstrates that FMR2 gene deletions may contribute to the FRAXE phenotype. Therefore, we suggest that screening for FMR2 gene deletions using array CGH should be considered in patients with non-specific XLID and absent trinucleotide expansion.