特發性低促性腺激素性腺功能低下症 臨床和基因方面探討

Abstract

<簡介> 特發性低促性腺激素性腺功能低下症(Idiopathic hypogonadotropic hypogonadism, IHH)是指下視丘至腦垂體結構正常，病患除促性腺激素低下，其他腦垂體賀爾蒙功能正常，導致其第二性徵發育不全，性腺功能低下。這類病人臨床表現通常有出生時陰莖短小、隱睪、青春期延遲或缺失，例如:女性沒有乳房發育或者無月經等。而根據有無合併嗅覺異常與否分成兩類：嗅覺喪失的卡門氏症候群(Kallmann syndrome)和嗅覺正常特發性低促性腺激素性腺功能低下症(normosmic IHH，nIHH)。 <實驗方法> 我們收集了33位診斷IHH病人，並分析其表徵、性腺賀爾蒙、骨齡和身高等臨床相關參數和實驗數據，並且利用全外顯子定序(whole exome sequencing)技術分析這些病人基因變異，以美國醫學遺傳學暨基因體學學會(ACMG)遺傳變異分類標準與指南尋找病患致病或可能致病基因。若未找出致病原因之病患，我們先探討寡基因變異（oligogenic variants）可能性和嘗試以拷貝數變異 (copy number variants)偵測基因的局部缺失或增加等分析工具，期找出可能的致病基因。仍找不到任何不明確的變異 (variants of uncertain significance)則納入全基因定序(whole genome sequencing)和RNA定序(RNA sequencing)來進一步確認病人可能的致病點位。 <結果> 本研究33位病人之中，20位找到致病或可能致病變異相關基因，其檢出率達60 %，其中FGFR1(n=6)、CHD7 (n=5)、ANOS1(n=4) 是找到最常見的致病基因之一。4位病人有不確定的致病基因，進一步分析後，其中3位可能存在雙基因或者寡基因變異。9位病人在外顯子定序檢測後未找到可能的基因變異者，其中4位進一步接受全基因及RNA定序檢查，1位病人在全基因定序中發現一個VUS點位。 <結論> 完整的基因分析可以幫助我們更及早診斷IHH病人，而且經由其致病基因相關綜合症IHH(syndromic IHH)協助病人做更完整的身體評估和檢查。另外，可以藉由一些基因檢測工具來彌補全外顯子分析的缺點來更加準確知道可能的致病基因。此項實驗有助於IHH相關基因的發現及了解其調控機制與致病機轉，甚至提供往後更完整檢驗和可能有效的治療方針。

Backgrounds: IHH is a rare condition characterized by gonadal failure due to deficiencies in the production, secretion, and activity of GnRH, with normal levels of other pituitary hormones and no anatomical abnormalities in the hypothalamus-pituitary axis. IHH is further divided into two subcategories: Kallmann syndrome (KS) and normosmic IHH (nIHH). Notably, there is currently no published clinical or genetic data on IHH patients in Taiwan. Methods: We applied whole exome sequencing (WES) to analysis our 33 IHH patients. Additionally, we categorized the phenotype of these patients, along with their hormone data and height outcomes after undergoing hormone replacement therapy. We also do further whole genome sequencing (WGS) and RNA-sequencing (RNA-seq) for those with uncertain variants and unknown variants. Results: The study revealed that 20 of them exhibited pathogenic/likely pathogenic (P/LP) variants of IHH-associated genes, yielding a mutation detection rate of 60%. Among these patients, FGFR1(n=6), CHD7(n=5) and ANOS1 (n=4) were the most frequent genetic causes of IHH. Nonetheless, we still encountered 13 patients who did not exhibit possible variants of the genes, including a group with variants of uncertain significance and variants (n=4) and a genetically unresolved group (n=9). Additionally, we remain committed to expanding our understanding of this condition and analysis them by cutting-edge tools and techniques, such as digenic/oligogenic variant prediction, copy number variant analysis, RNA-Seq, and WGS. Only four patients were included in our RNA-seq and WGS data collection, and among them, 1 patient was identified with a variant of uncertain significance (VUS). Conclusion: To sum up, this study effectively determined the genetic origins of the majority (60%) of IHH cases, with a greater occurrence found among male patients. Utilizing exome sequencing combined with targeted analysis of IHH-related genes was a successful approach to uncovering the genes for the disease, both known and unknown. Further cases are needed to provide additional evidence for the effectiveness of RNA-seq and WGS in IHH patients.