Institute of Genetic Medicine, Johns Hopkins Medical Institutions, Baltimore, MD 21287, USA.
J Med Genet. 2011 May;48(5):323-6. doi: 10.1136/jmg.2010.083931. Epub 2010 Nov 19.
Trisomy 13 occurs in 1/10,000-20,000 live births, and mosaicism accounts for 5% of these cases. Phenotype and outcome of mosaic trisomy 13 are variable and poorly understood. Microsatellite analyses of trisomy 13 have indicated the high incidence of maternal meiotic origin and reduced recombination, but no study has focused on mosaic trisomy 13 in live born patients.
Single-nucleotide polymorphism (SNP) array, fluorescence in situ hybridisation and bioinformatics analyses were performed in three cases of mosaic trisomy 13. Two cases of complete mosaic trisomy 13 originated from meiosis I non-disjunction followed by trisomic rescue; one had crossovers resulting in segmental uniparental disomy in the disomic line, and one had no crossover. Mosaicism for partial trisomy 13 in the third complex case either arose from meiosis II non-disjunction without crossover or in early mitosis followed by anaphase lags. The extra chromosome 13 was maternal in origin in all three cases. Mosaicism percentage calculated from B allele frequencies ranged from 30 to 50.
Genotypes and copy number information provided by SNP array allow determination of parental origin and uniparental disomy status and direct quantification of mosaicism. Such information may lead to a better understanding of mechanisms underlying mosaic aneuploidies and the observed phenotypic variability and better prediction of recurrent risk.
三体 13 发生在每 10000-20000 例活产中，其中镶嵌型占 5%。镶嵌型三体 13 的表型和结局具有变异性且了解甚少。三体 13 的微卫星分析表明母源减数分裂来源和减少重组的发生率较高，但尚无研究关注活产患者中的镶嵌型三体 13。
对三例镶嵌型三体 13 进行了单核苷酸多态性 (SNP) 微阵列、荧光原位杂交和生物信息学分析。两例完全镶嵌型三体 13 源自减数分裂 I 非分离，随后三体挽救；一例发生交叉，导致二倍体系的片段单亲二体性，一例无交叉。第三例复杂镶嵌型部分三体 13 要么源自无交叉的减数分裂 II 非分离，要么源自早期有丝分裂后后期滞后。所有三例额外的 13 号染色体均来自母源。从 B 等位基因频率计算的镶嵌率范围为 30%至 50%。
SNP 微阵列提供的基因型和拷贝数信息可确定亲本来源和单亲二体性状态，并直接定量镶嵌型。这些信息可能有助于更好地理解镶嵌性非整倍体的发生机制以及观察到的表型变异性，并更好地预测复发性风险。
