Loss of the KH1 domain of FMR1 in humans due to a synonymous variant causes global developmental retardation.

•Fragile X syndrome is a common cause of intellectual disability.•Very few FMR1 pathological single nucleotide variants have been reported.•A new synonymous variant in the FMR1 gene produces an aberrant transcript without exon 8.•This synonymous variant was associated with an unspecific clinical presentation.