新生兒篩檢原發性肉鹼缺乏症R254X基因突變之研究

Abstract

背景： 原發性肉鹼缺乏症是因為細胞膜上的肉鹼運輸器有缺陷，導致肉鹼由尿液排出，造成體內肉鹼缺乏所引起的一種體染色體隱性遺傳的脂肪酸代謝異常疾病。目前藉由新生兒篩檢系統，使用串聯質譜儀來偵測血片游離肉鹼濃度，可發現尚未出現徵狀的新生兒與母親。但也因為母血效應的影響，暗示有部分的患嬰無法被篩檢出來，有偽陰性存在。

方法： 本研究是在篩檢流程上利用串聯質譜儀分析血片的游離肉鹼濃度進行初篩，首先調高cut-offs，再搭配在臺灣新生兒常見的突變基因p.R254X分析，做為第二線的篩檢工具，希望能提高新生兒篩檢在原發性肉鹼缺乏症的検出率。

結果： 我們在30,237個新生兒當中有206件因為游離肉鹼濃度初檢數值低於cut-offs，需要複檢而進入p.R254X基因分析。實驗結果顯示，發現12個帶有p.R254X突變基因的帶原者，得到p.R254X基因帶原率是1/2,520。然而，另外發現1個確認陽性個案，但其突變基因型卻不包含p.R254X。預估原發性肉鹼缺乏症在臺灣的發生率是1/30,237。

結論與展望： 對於原發性肉鹼缺乏症的篩檢，使用串聯質譜儀偵測血液的游離肉鹼濃度仍是一個可靠的方法。雖然本研究未能增加此症之檢出率，但原發性肉鹼缺乏症是一個很重要的疾病，未來仍需繼續努力。

Background：Primary carnitine deficiency (PCD) is an autosomal recessive fatty acid oxidation disease caused by a defect of carnitine transporter across the cell membrane, and then carnitine is excreted through the kidney and intracellular carnitine is deficiency. Tandem mass spectrometry (MS/MS) screening of newborns can detect both asymptomatic newborns and mothers, but the maternal effects may be one of the reasons for false-negative.

Methods：We first used MS/MS to measure free carnitine level in dried blood spots. We elevated the free carnitine cut-offs, and then combined p.R254X molecular analysis as the second tier analysis tool in the newborn screening flow-chart. Because of p.R254X is the most common mutation in Taiwanese newborns. The goal is to improve the detection rates of PCD.

Results：Out of 30,237 newborn, there were 206 samples which free carnitine levels lower than the cut-offs in the initial screening card and the follow-up samples were requested. We found 12 heterozygote of p.R254X, the carrier rate of p.R254X was 1/2,520.Among them, however, only one newborn was confirmed as a case of PCD, whose genotype dose not contain p.R254X. Therefore, the incidence of newborn with PCD in this study is 1/30,237.

Conclusion：The MS/MS is still a reliable method for detecting PCD.PCD is a very serious disease. Although this study failed to enhance the detection rate of this disease, we should continue to make more discoveries and put more efforts in this study.