Fragile X Syndrome Caused by Maternal Somatic Mosaicism of Gene: Case Report and Literature Review

Fragile X syndrome (FXS) is caused by an abnormal expansion of the number of trinucleotide CGG repeats located in the 5' UTR in the first exon of the gene. Size and methylation mosaicisms are commonly observed in FXS patients. Both types of mosaicisms might be associated with less severe phenotypes depending on the number of cells expressing FMRP. Although this dynamic mutation is the main underlying cause of FXS, other mechanisms, including point mutations or deletions, can lead to FXS. Several reports have demonstrated that deletions including the entire or a portion of the gene end up with the absence of FMRP and, thus, can lead to the typical clinical features of FXS. However, very little is known about the clinical manifestations associated with gene deletions in mosaicism. Here, we report an FXS case caused by an entire hemizygous deletion of the gene caused by maternal mosaicism. This manuscript reports this case and a literature review of the clinical manifestations presented by carriers of gene deletions in mosaicism.