Dutly F, Balmer D, Baumer A, Binkert F, Schinzel A
Institute of Medical Genetics, University of Zürich, Switzerland.
Eur J Hum Genet. 1998 Mar-Apr;6(2):140-4. doi: 10.1038/sj.ejhg.5200168.
In a recent study Bugge et al and Kotzot et al reported that isochromosomes 18p originate mainly from maternal meiosis II nondisjunction, followed by misdivision. In order to determine if there is a common mechanism for isochromosome formation, three cases with mosaicism for an additional isochromosome 12p and three cases with tetrasomy 9p were studied. Two probands with isochromosomes 12p and the three cases with isochromosome 9p showed 3 alleles (two different maternal alleles and one paternal allele) at several loci mapping to distal 12p and 9p, respectively. Maternal heterozygosity for distal markers was reduced to homozygosity for markers closer to the centromere in both i(12p) cases and in one i(9p) case. For one patient with isochromosome 12p, the maternal band was clearly stronger than the paternal one at some loci, but two distinct maternal alleles were never seen. For one foetus and the patient with tetrasomy 9p, distal markers showed maternal heterozygosity. All proximal markers were not informative in these two i(9p) cases. Our findings indicate common features in different autosomal isochromosomes: the origin of the isochromosomes analysed in predominantly maternal; and a common mechanism appears to underlie their formation, namely due to meiosis II nondisjunction followed by a rearrangements leading to duplication of the short and loss of the long arm.
在最近的一项研究中，布格等人和科佐特等人报告称，18号等臂染色体主要源自母本减数分裂II不分离，随后发生错分裂。为了确定等臂染色体形成是否存在共同机制，对3例额外的12号等臂染色体嵌合体病例和3例9号染色体四体病例进行了研究。2例12号等臂染色体先证者和3例9号等臂染色体病例在分别定位于12号染色体短臂远端和9号染色体短臂远端的几个位点上显示出3个等位基因（两个不同的母本等位基因和一个父本等位基因）。在两例i(12p)病例和一例i(9p)病例中，靠近着丝粒的标记的母本杂合性都降低为纯合性。对于一例12号等臂染色体患者，在某些位点母本条带明显强于父本条带，但从未见过两个不同的母本等位基因。对于一例胎儿和9号染色体四体患者，远端标记显示母本杂合性。在这两例i(9p)病例中，所有近端标记均无信息价值。我们的研究结果表明，不同常染色体等臂染色体具有共同特征：所分析的等臂染色体主要源自母本；其形成似乎有一个共同机制，即由于减数分裂II不分离，随后发生重排，导致短臂重复和长臂缺失。
