[Tissue heterogeneity analysis of CGG-repeat mutation in two fragile X affected male fetuses]
1The State Key Laboratory of Medical Genetics and School of Life Sciences, Central South University, Changsha 410078, China.
Objective:
To compare the CGG-repeat-length and its methylation status in fetal tissues and to explicate the heterogeneity of CGG repeats.
Method:
Multiple tissues from a full mutation(August 2013) and a mosaic aborted fetus of 23-week gestation(May 2012) were collected and genomic DNA from these tissues was extracted. The CGG-repeat-length and methylation status in fetal tissues were determined by a combined strategy of Southern blotting and GC-Rich PCR. FMR1 expression was measured by real time PCR and Western blotting.
Result:
CGG-repeat-length in different tissues of each fetus was similar.A major methylated band in the full mutation range (540 CGG repeats) was detected in the brain, skin, testis and kidney tissues of Case 1. An unmethylated premutation band with 160 CGG repeats, and another two bands with 470 and 1 100 CGG repeats in the full mutation range were shown in the brain, skin, testis, lung, stomach, gut, liver, kidney, heart and blood of Case 2. However, the methylation status of CGG repeats in the mosaic fetus was heterogeneous among different tissues. The lowest premutation ratio was in the brain of the mosaic fetus compared with other tissues, and correspondingly FMR1 expression in its brain was minimum.
Conclusion:
This study clarify the tissue heterogeneity of CGG repeats and provides information for the genetic counseling and clinical diagnosis in fragile X syndrome. Based on the fact that the mosaic fetus' mother is a carrier of full mutation, it is speculated that the maternal CGG repeat has contracted before the differentiation of trilaminar germ disc.
