两个伴皮层下囊肿的巨脑性白质脑病家系的产前诊断

Prenatal diagnosis of two families with megalencephalic leukoencephaiopathy with subcorticai cysts

目的对2个基因诊断明确的伴皮层下囊肿的巨脑性白质脑病（megalencephalicleukoencephalopathywithsubcorticalcysts，MLC）家系进行遗传咨询和产前分子诊断。方法先证者1和2分别于2011年6月和2009年6月在北京大学第一医院儿科就诊，采集先证者及其父母外周静脉血提取基因组DNA，采用DNA测序技术进行MLCl基因检测。先证者之母再次妊娠后，分别通过羊膜腔穿刺（孕21周“，胎儿1）和绒毛穿刺（孕12周”，胎儿2）采集羊水及绒毛标本。提取胎儿基因组DNA，应用DNA直接测序技术检测胎儿是否具有与先证者一致的MLCl基因突变类型，并通过聚合酶链反应技术扩增Y染色体性别决定区以及X染色体微卫星标记（AR、DXS6807和DXS6797）进行单体型分析判断胎儿羊水／绒毛中是否有母体细胞污染。胎儿出生后进行验证及电话随访。结果先证者1和2具有大头、运动发育落后及典型MLC头颅MRI表现，符合MLC的临床诊断。先证者lMLCl基因检出c．353C〉T（p．T118M）、c．803C〉G（p．T268R）复合杂合突变；先证者2检出c．353C〉T（p．T118M）和c．836T〉C（p．L279P）复合杂合突变。均基因确诊MLC。胎儿lMLCl基因相应位点发现c．803C（野生型）和c．353C〉T（p．Tl18M）杂合改变；胎儿2相应位点均为野生型（c．353C和c．836T）。且胎儿基因组DNA均无母体细胞污染。胎儿1生后基因验证结果与产前诊断结果一致，5月龄时头围及生长发育均正常；胎儿2现生后1个月，无巨颅，尚未进行生后验证。结论检测胎儿基因组DNA是否具有与先证者相同的MLCl基因突变类型，可对基因诊断明确的MLC家庭提供准确的产前分子诊断。通过Y染色体性别决定区及3个x染色体微卫星标记进行单体型分析可有效判断胎儿基因组中是否存在母体细胞污染，有助于排除母体细胞污染对产前诊断结果的影响，保证产前诊断结果的可靠性。

Objectives To provide genetic counseling and prenatal molecular diagnosis for two families with megalencephalic leukoencephalopathy with subcortical cysts （MLC）. Methods Two MLC patients （probands l and 2） were admitted to the Department of Pediatrics of Peking University First Hospital in June 2011 and June 2009, respectively. Peripheral blood was collected and DNA sequencing was performed for genetic analysis for the two MLC patients and their parents. Amniotic fluid and villus of two fetuses （fetus 1 and 2） were collected at 21＋4 and 12＋3 weeks of gestational age from their mothers when they were pregnant again. The genomic DNA of the two fetuses was extracted and corresponding sites of MLC1 gene were sequenced. Haplotype analysis using a combination of 3 microsatellite markers （AR, DXS6807 and DXS6797） on chromosome X and sex-determining region of Y chromosome was performed to detect maternal cell contamination. Verification of the prenatal molecular diagnosis and follow-up study after birth were conducted for both fetuses. Results Macrocephaly, motor development delay and typical findings on brain MRI were identified in the two probands, and were clinically diagnosed with MLC. Compound heterozygous mutations were detected in proband 1 [c.353C〉T （p.T118M） and c.803C〉G （p.T268R）] and proband 2 [c.353C〉T （p.T118M） and c.836T〉C（p.L279P）], respectively. MLC was genetically diagnosed. Heterozygous variation in c.353[c.353C〉T （p.TII8M）] and wild c.803C were identified in fetus 1, and both wild c.353C and c.836T were found in fetus 2. No maternal cell contamination was detected in both fetuses. Sequencing the corresponding sites after birth confirmed the prenatal diagnosis, and the head circumference and motor development were normal in fetus 1 at 5 months old. No macrocephaly was found and no DNA sequencing was done in fetus 2 at one month old. Conclusions Genetic counseling and prenatal molecular diagnosis for MLC families combined with clinical and genetic diagnosis are important in preventing MLC. Haplotype analysis with a combination of three microsatellite markers on chromosome X and sex-determining region of Y chromosome is useful in detecting maternal cell contamination and avoiding its influence on prenatal diagnosis, and confirming the reliability of prenatal diagnosis.