Preconception and antenatal screening for the fragile site on the X-chromosome

 

Abstract

Background

Fragile X is the most common cause of mental retardation after Down syndrome. It is the commonest inherited cause of mental retardation, and results from a dynamic mutation in a gene on the long arm of the X chromosome. Various strategies are used for prenatal screening.

Objectives

To determine whether preconceptional or antenatal screening for fragile X carrier status in apparently low-risk women confers any additional benefit over the existing practice of offering testing to women thought to be at increased risk.

Search methods

We searched the Cochrane Pregnancy and Childbirth Group's Trials Register (October 2008).

Selection criteria

Randomised clinical trials comparing women being tested regardless of family history (intervention group) with women tested only when there is a family history of either fragile X and/or other undiagnosed mental illness/impairment (control group).

Data collection and analysis

Three review authors independently assessed trial quality.

Main results

No trials were included.

Authors' conclusions

No information is available from randomised trials to indicate whether routine preconceptional or antenatal screening for fragile X carrier status confers any benefit over testing women thought to be at increased risk.

 

Plain language summary

Preconception and antenatal screening for the fragile site on the X-chromosome

No strong evidence to show who, other than women at risk, should be screened before or during pregnancy for fragile X syndrome.

Fragile X syndrome is caused by an inherited genetic defect that can result in mental disability. There is no way of reversing the syndrome. Although it runs in families, many people do not realise they are carriers until they have an affected child. A blood test can identify whether a person is a carrier, and therefore whether a test on the unborn baby is worthwhile. Currently, only women who are thought to be more likely to pass on fragile X are offered testing before or during pregnancy. There are no trials to show whether offering the test to everyone is worthwhile.

 

摘要

背景

針對在X染色體上的脆裂點(fragile site)進行受孕前與產前的篩檢

除了在唐氏症(Down syndrome)之外，脆裂的X染色體是最常見智能缺陷的原因。它是最常見的遺傳性智能缺陷成因，是來自於X染色體長臂上的某個基因中之變動性突變(dynamic mutation)。針對產前的掃描，會使用很多不同的策略。

目標

相對於目前只對風險高的婦女們來測試是否攜帶脆裂的X染色體，評估在風險性明顯很低的婦女進行的受孕前或產前掃描是否會有任何額外的優點。

搜尋策略

我們搜尋了the Cochrane Pregnancy and Childbirth Group trials register(2002年11月)、the Cochrane Central Register of Controlled Trials(The Cochrane Library，Issue 4，2002年)、MEDLINE(1980年一月到2002年十月)，以及這些文章的參考文獻清單。

選擇標準

不論家族史而接受測試的婦女(實驗組)，以及僅限於具有脆裂的X染色體及/或其他未檢測過的智能疾病/不全症之家族史而接受測試的婦女(對照組)，這些隨機的臨床試驗將這2組之間進行了比較。

資料收集與分析

有3位審稿者獨立地評估了試驗的品質。

主要結論

其中沒有包含任何試驗。

作者結論

常規針對脆裂的X染色體帶原者之狀態所進行的受孕前或產前掃描，是否能夠在帶來任何好處，並不能從隨機的試驗中取得任何足以證實的資訊。

翻譯人

此翻譯計畫由臺灣國家衛生研究院(National Health Research Institutes, Taiwan)統籌。

總結

針對X染色體脆折症(Fragile X Syndrome)，在懷孕之前或懷孕期間，除了那些處於風險中的婦女之外，並沒有強烈的證據顯示哪些人應該要接受掃描。X染色體脆折症是由某種遺傳性的基因缺陷所引起，而這樣的缺陷可能會造成智能不足。目前還沒有方法可以扭轉這樣的症狀。雖然這樣的基因缺陷會在家人之中流傳，但是除非他們生下了受到影響的孩子，否則很多人並不清楚他們本身也是基因的帶原者。血液測試可以確認某個人是否為帶原者，因此還能決定在未出生的嬰兒身上所進行的測試是否有價值。目前，只有那些被認為較有可能攜帶脆裂之X染色體的婦女，醫療人員才會在她們懷孕之前或懷孕期間提供測試。並沒有任何試驗可以顯示，對於所有的人都提供測試是否具有價值。