Other times it can be a gene mutations, like BRCA1, or in a syndrome like Fragile X syndrome, which is caused by the expansion of a trinucleotide repeat within a gene on the X chromosome.

某些情况下可能是基因突变，如BRCA1；也可能是像脆性X染色体综合征这样的综合征，这是由于X染色体上某基因内的三核苷酸重复扩增引起的。