Objectives To report an unusual case of MCT8 deficiency (Allan–Herndon–Dudley syndrome), an X-linked condition caused by pathogenic variants in the SLC16A2 gene. Defective transport of thyroid hormones (THs) in this condition leads to severe neurodevelopmental impairment in males, while heterozygous females are usually asymptomatic or have mild TH abnormalities. Case presentation A girl with profound developmental delay, epilepsy, primary amenorrhea, elevated T3, low T4 and free T4 levels was diagnosed with MCT8-deficiency at age 17 years, during evaluation for primary ovarian insufficiency (POI). Cytogenetic analysis demonstrated balanced t(X;16)(q13.2;q12.1) translocation with a breakpoint disrupting SLC16A2. X-chromosome inactivation studies revealed a skewed inactivation of the normal X chromosome. Conclusions MCT8-deficiency can manifest clinically and phenotypically in women with SLC16A2 aberrations when nonrandom X inactivation occurs, while lack of X chromosome integrity due to translocation can cause POI.

中文翻译：

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一名原发性卵巢功能不全少女的 X 连锁 MCT8 缺陷（Allan-Herndon-Dudley 综合征）的晚期诊断

目的 报告一例罕见的 MCT8 缺陷病例（Allan-Herndon-Dudley 综合征），这是一种由 SLC16A2 基因致病性变异引起的 X 连锁疾病。在这种情况下，甲状腺激素（TH）的运输缺陷会导致男性严重的神经发育障碍，而杂合女性通常无症状或有轻微的 TH 异常。病例介绍 一名患有严重发育迟缓、癫痫、原发性闭经、T3 升高、T4 和游离 T4 水平降低的女孩在 17 岁时在原发性卵巢功能不全 (POI) 评估过程中被诊断为 MCT8 缺乏症。细胞遗传学分析证明平衡的 t(X;16)(q13.2;q12.1) 易位具有破坏 SLC16A2 的断点。 X 染色体失活研究揭示了正常 X 染色体的倾斜失活。结论 当发生非随机 X 失活时，MCT8 缺陷可在具有 SLC16A2 畸变的女性中表现出临床和表型，而易位导致的 X 染色体完整性缺失可导致 POI。