Miyoshi O, Kondoh T, Taneda H, Otsuka K, Matsumoto T, Niikawa N
Department of Human Genetics, Nagasaki University School of Medicine, Japan.
J Med Genet. 1999 Apr;36(4):326-9.
Maternal uniparental disomy for chromosome 7 (UPD7) may present with a characteristic phenotype reminiscent of Silver-Russell syndrome (SRS). Previous studies have suggested that approximately 10% of SRS patients have maternal UPD7. We describe a girl with a mos47,XX,+mar/46,XX karyotype associated with the features of SRS. Chromosome painting using a chromosome 7 specific probe pool showed that the small marker was a ring chromosome 7 (r(7)). PCR based microsatellite marker analysis of the patient detected only one maternal allele at each of 16 telomeric loci examined on chromosome 7, but showed both paternal and maternal alleles at four centromeric loci. Considering her mosaic karyotype composed ofdiploid cells and cells with partial trisomy for 7p13-q11, the allele types obtained at the telomeric loci may reflect the transmission of one maternal allele in duplicate, that is, maternal UPD7 (complete isodisomy or homodisomy 7), whereas those at the centromeric loci were consistent with biparental contribution to the trisomic region. It is most likely that the patient originated in a 46,XX,r(7) zygote, followed by duplication of the maternally derived whole chromosome 7 in an early mitosis, and subsequent loss of the paternally derived ring chromosome 7 in a subset of somatic cells. The cell with 46,XX,r(7) did not survive thereafter because of the monosomy for most of chromosome 7. If the putative SRS gene is imprinted, it can be ruled out from the 7p11-q11 region, because biparental alleles contribute to the region in our patient.
母源7号染色体单亲二倍体（UPD7）可能表现出类似于Silver-Russell综合征（SRS）的特征性表型。既往研究提示，约10%的SRS患者存在母源UPD7。我们描述了一名核型为mos47,XX,+mar/46,XX且具有SRS特征的女孩。使用7号染色体特异性探针池进行染色体描绘显示，小标记物是一条7号环状染色体（r(7)）。对该患者进行基于PCR的微卫星标记分析，在7号染色体上检测的16个端粒位点中，每个位点仅检测到一个母源等位基因，但在4个着丝粒位点显示出父源和母源等位基因。考虑到她的嵌合核型由二倍体细胞和7p13-q11部分三体细胞组成，端粒位点获得的等位基因类型可能反映了一个母源等位基因的重复传递，即母源UPD7（完全等二体或7号染色体同二体），而着丝粒位点的等位基因类型与三体区域的双亲贡献一致。很可能该患者起源于一个46,XX,r(7)合子，随后在早期有丝分裂中母源来源的整条7号染色体发生重复，随后在一部分体细胞中父源来源的环状7号染色体丢失。此后，具有46,XX,r(7)的细胞因7号染色体大部分区域单体而无法存活。如果假定的SRS基因是印记基因，那么可以将7p11-q11区域排除在外，因为在我们的患者中该区域有双亲等位基因的贡献。
