脆性X综合征是一种引起人类智力低下的X—连锁遗传病。该病于1976年得到细胞遗传学确诊,其细胞遗传学特征是在X染色体长臂二区7带存在一个脆性位点[记为fra(X)(q27)。有趣的是,脆性X染色体可以通过表型正常的男性携带者传递给女儿,再由女儿传递到外孙时就会引起智力低下等临床异常。另外,还有35%的女性携带者表现出某种程度的智力低下。该病复杂的发病规律吸引了世界各国研究者的关注,我国自1984年开始见有该病的报告,而云南省尚未见有报道。1992年8月,一对夫妇到我院计划生育科作遗传咨询,自诉曾生育3胎,1女2男。女儿现年13岁,发育正常;大儿子现年11岁,体格发育无明显异常,智力发育迟缓,至今不能辨认亲属,不识数,不能配合智商测验;小儿子现年9岁,体格发 Fragile X syndrome is a type of X-linked genetic disorder that causes low mental status in humans. The disease was diagnosed cytogenetically in 1976 with a cytogenetically characterized presence of a fragile site in the second-zone 7 of the long arm of the X chromosome [fra (X) (q27)]. Interestingly, the fragile X chromosome can be passed on to a daughter by a normal phenotypic male carrier and then transmitted by a daughter to a grandson, which can cause clinical abnormalities such as mental retardation. In addition, 35% of female carriers showed some degree of mental retardation. The complex incidence of the disease has attracted the attention of researchers from all over the world. Since 1984, China has seen the report of the disease, but no reports have been reported in Yunnan Province. In August 1992, a couple went to the Family Planning Section in our hospital for genetic counseling. They had 3 children and 1 woman and 2 men. Her daughter is now 13 years old, normal development; eldest son is now 11 years old, no significant physical development, mental retardation, so far can not identify relatives, unknown, can not meet the IQ test; the youngest son is 9 years old, physical hair