Autosomal ring chromosomes are rare cytogenetic findings that arise from breakage and fusion of the chromosome ends. Rings are mitotically unstable, usually sporadic and associated with a 'ring syndrome', characterized by a variable phenotype: growth retardation, no significant dysmorphisms and normal to moderately disabled intelligence. We describe the clinical features and molecular characterization of two sisters with ring chromosome 4. Karyotype analysis was performed on both sisters and parents. Chromosome microarray was performed on both sisters to delineate the breakpoint imbalance. Both sisters had a large ring 4 chromosome in the majority of cells analyzed on karyotype. Microarray results were identical in the sisters, showing a 55.8 kb duplication on the terminal 4p arm and a 1.5 Mb deletion on the terminal 4q arm. No genes of interest were identified in these regions. Parental karyotypes on lymphocytes and fibroblasts were normal, with no finding of mosaicism for the ring 4 chromosome. Polymorphic marker analysis revealed the maternal origin of the ring. To our knowledge, this is the first reported instance of a ring 4 chromosome recurring in siblings after extensive parental testing, which suggests this was due to maternal gonadal mosaicism.

中文翻译：

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两姐妹几乎完整的 4 号环染色体的临床和分子特征，由于性腺嵌合而复发。

常染色体环染色体是罕见的细胞遗传学发现，由染色体末端的断裂和融合引起。环是有丝分裂不稳定的，通常是散发性的，并与“环综合征”相关，其特征是可变的表型：生长迟缓、无明显畸形和智力正常至中度残疾。我们描述了带有 4 号环染色体的两姐妹的临床特征和分子特征。对姐妹和父母进行了核型分析。对两姐妹进行染色体微阵列分析以描绘断点不平衡。在核型分析的大多数细胞中，两姐妹都有一条大的环 4 染色体。姐妹中的微阵列结果相同，显示末端 4p 臂上有 55.8 kb 的重复，而末端 4q 臂上有 1.5 Mb 的缺失。在这些区域中没有发现感兴趣的基因。淋巴细胞和成纤维细胞的亲本核型正常，未发现环 4 染色体嵌合。多态性标记分析揭示了环的母系起源。据我们所知，这是第一个报道的经过广泛的父母测试后，兄弟姐妹中重复出现 4 环染色体的实例，这表明这是由于母体性腺嵌合所致。