The rare genetic character of fra(X) is that there are NTFs and NTMs, their pre - mutation may be transmitted to their grandsons and great - grandsons through their daugh-ters.

• 脆性X综合征最罕见的遗传特点是存在正常传递男子,而且他的前突变可通过其女儿传至其孙子及曾孙。