脆性 X 综合征是家族性智力低下的最常见病因,以数量异常的 CCG 重复构成遗传DNA 序列为其特征。该 DNA 在有丝分裂和减数分裂时均不稳定。作者认为这些遗传不稳定的 DNA 顺序也可能在基因组的其它部位存在,并可能解释经典遗传机理所无法解释的许多遗传问题,如早现遗传,不完全外显率,变量表达和可能的印迹(imprinting),花斑及多因子遗传。 Fragile X syndrome is the most common cause of familial mental retardation, characterized by an abnormal number of CCG repeats constituting genetic DNA sequences. The DNA is not stable at mitosis and meiosis. The authors believe that these genetically unstable DNA sequences may also exist elsewhere on the genome and may explain many of the genetic issues that classical genetic mechanisms can not explain, such as early onset inheritance, incomplete penetrance, variable expression and possible imprinting imprinting, plaque and multifactorial inheritance.