Jenkins E C, Brown W T, Schonberg S, Krawczun M S, Goldberg J, Golbus M S
Department of Genetics, New York State Institute for Basic Research in Developmental Disabilities Staten Island 10314.
Am J Med Genet. 1992;43(1-2):128-35. doi: 10.1002/ajmg.1320430120.
Recently, we detected fra(X)(q27.3) in amniocyte cultures from female identical twins. The pregnant woman did not exhibit fra(X)(q27.3) in whole blood cultures but was the sister of 2 affected brothers. DNA marker analyses showed that she was a carrier of FRAXA. Amniotic fluid cultures (AFCs) from twins A and B exhibited the fragile X [fra(X)] chromosome, but the level of cytogenetic expression was very low in twin A's AFCs. DNA marker studies indicated both twins were carriers of FRAXA. Peripheral umbilical blood sample (PUBS) cultures exhibited fra(X)(q27.3) at a frequency of about 10% for both twins. DNA fingerprinting indicated that the twins were identical, confirming the clinical impression, with a very thin separating amniotic membrane. To our knowledge, this is the only report of prenatal fra(X)(q27.3) detection in female identical twins, and the second report of identical twin detection [Rocchi et al., 1985]. We have diagnosed prenatally fra(X)(q27.3) in 5 female fetuses using AFCs. The average fra(X) frequency was 4% for these positive female fetuses with a range of 0.5% to 8.5%. Follow-up whole blood studies confirmed our original results at an average fra(X) frequency of 25%.
最近，我们在一对女性同卵双胞胎的羊水细胞培养物中检测到fra(X)(q27.3)。该孕妇全血培养物中未表现出fra(X)(q27.3)，但其是2名患病兄弟的姐妹。DNA标记分析显示她是FRAXA的携带者。双胞胎A和B的羊水培养物（AFC）中出现了脆性X [fra(X)] 染色体，但双胞胎A的AFC中细胞遗传学表达水平非常低。DNA标记研究表明这对双胞胎都是FRAXA的携带者。外周脐血样本（PUBS）培养物中，这对双胞胎的fra(X)(q27.3)出现频率约为10%。DNA指纹图谱表明这对双胞胎是同卵的，这与临床判断相符，她们之间的羊膜分隔非常薄。据我们所知，这是关于女性同卵双胞胎产前检测到fra(X)(q27.3)的唯一报告，也是同卵双胞胎检测的第二份报告[罗基等人，1985年]。我们使用AFC对5名女性胎儿进行了产前fra(X)(q27.3)诊断。这些阳性女性胎儿的fra(X)平均频率为4%，范围在0.5%至8.5%之间。后续的全血研究证实了我们最初的结果，fra(X)平均频率为25%。
