Complex structural X chromosome abnormalities are rare in humans and animals, and not recurrent. Yet, each case provides a fascinating opportunity to evaluate X chromosome content and functional status in relation to the effect on the phenotype. Here, we report the first equine case of a complex unbalanced X-autosome rearrangement in a healthy but short in stature Thoroughbred mare. Studies of about 200 cells by chromosome banding and FISH revealed an abnormal 2n = 63,X,der(X;16) karyotype with a large dicentric derivative chromosome (der). The der was comprised of normal Xp material, a palindromic duplication of Xq12q21, and a translocation of chromosome 16 to the inverted Xq12q21 segment by the centromere, whereas the distal Xq22q29 was deleted from the der. Microsatellite genotyping determined a paternal origin of the der. While there was no option to experimentally investigate the status of X chromosome inactivation (XCI), the observed mild phenotype of this case suggested the following scenario to retain an almost normal genetic balance: active normal X, inactivated X-portion of the der, but without XCI spreading into the translocated chromosome 16. Cases like this present unique resources to acquire information about species-specific features of X regulation and the role of X-linked genes in development, health, and disease.

中文翻译：

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纯种母马新的复杂不平衡双着丝粒 X 常染色体重排对表型有轻微影响

复杂的结构性 X 染色体异常在人类和动物中很少见，并且不会复发。然而，每个案例都提供了一个很好的机会来评估 X 染色体含量和功能状态与对表型的影响有关。在这里，我们报告了第一个在健康但身材矮小的纯种母马中复杂不平衡 X 常染色体重排的马病例。通过染色体显带和 FISH 对大约 200 个细胞的研究揭示了一个异常的 2n = 63,X,der(X;16) 核型，带有一个大的双着丝粒衍生染色体 (der)。der 由正常 Xp 材料、Xq12q21 的回文重复和着丝粒将 16 号染色体易位到反向 Xq12q21 片段组成，而远端 Xq22q29 从 der 中删除。微卫星基因分型确定了 der 的父本起源。