The occurrence of monochorionic diamniotic twins with sex discordance is a very rare phenomenon. We present a case of spontaneously conceived gender-discordant monochorionic diamniotic twins born to a 23-year-old female, both twins demonstrating similar blood karyotype 45,X/46,X, idic(Y) and a novel 99 kb mutation at 3p24.3 involving exons 15-16 of transcript NM_001134381.1 of the Tre-2/Bub2/Cdc16 Domain Family Member 5 (TBC1D5) gene. The male twin showed no anatomic abnormalities and pelvic ultrasound revealed descended gonads. The female twin had a horseshoe-shaped kidney, normal uterus, and intra-abdominal gonads. The blood karyotype and microarray studies revealed similar distribution of X and isodicentric Y chromosome along with a novel genetic mutation which has not been previously reported. Our case findings not only report Turner syndrome mosaicism with a novel genetic mutation but also stress the importance of clinical follow-up of twins in order to evaluate the functional abnormalities associated with isodicentric Y chromosomes including germ cell tumors.

中文翻译：

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具有 45,X/46,X、Idic(Y) 镶嵌现象和 TBC1D5 基因内的新缺失的性别不一致的单绒毛膜双羊膜双胞胎。

出现性别不一致的单绒毛膜双羊膜双胞胎是一种非常罕见的现象。我们展示了一个自然受孕的性别不一致的单绒毛膜双羊膜双胞胎案例，该双胞胎出生于一名 23 岁女性，这对双胞胎表现出相似的血核型 45,X/46,X、idic(Y) 和 3p24 处的新 99 kb 突变。 3 涉及 Tre-2/Bub2/Cdc16 域家族成员 5 (TBC1D5) 基因转录本 NM_001134381.1 的外显子 15-16。男双胞胎没有显示解剖异常，盆腔超声显示性腺下降。这对女性双胞胎有一个马蹄形的肾脏、正常的子宫和腹腔内的性腺。血液核型和微阵列研究揭示了 X 和等双着丝粒 Y 染色体的相似分布以及以前未报道过的新基因突变。