脆性X[fra(X)]与智力发育迟缓的关系是肯定的。已有报告,它在智力低下男性中的发生率为2～9%不等。大约有1/3的女性脆性X携带者为杂合子型。脆性X发生率为智力低下女性的0.4%。根据到目前为止唯一的人口研究(Sutherland,1982年),罕见的常染色体脆性部位的发生率是智力低下人群的0.95%,是新生儿的0.098%。作者对芬兰南部Espoo和Vantaa两市 The relationship between fragile X [fra (X)] and mental retardation is affirmative. It has been reported that it occurs in 2-9% of men with mental retardation. About one-third of women with fragile X carriers are heterozygous. Fragile X incidence of mental retardation in women 0.4%. According to the only population study so far (Sutherland, 1982), rare chromosomal fragility sites occur in 0.95% of people with impaired intelligence and 0.098% of those in newborns. The author of the two cities of Espoo and Vantaa in southern Finland