Molecular diagnosis of fragile X syndrome in a female child

Abstract

목 적: 취약 X 증후군(fragile X syndrome)은 FMR1 유전자의 5’ 비해독부위에 있는 CGG 3염기 반복의 확장에 의해 발생되는 유전성 질환이다.

방 법: 본 연구에서는 임상 소견과 핵형분석에서 취약 X 증후군으로 진단 받은 여아 환자와 그 부모를 대상으로 Abbott Molecular Fragile X PCR Kit를 이용하여 CGG 3염기 영역을 PCR로 증폭하여 normal, premutation, full mutation의 CGG 반복의 유형을 확인하였으며, premutation과 normal allele의 경우에는 정확한 CGG 반복수를 분석하였다.

결 과: 환자는 30회와 >200회의 CGG 3염기가 반복된 FMR1 대립유전자를 갖고 있는 것으로 확인되어 취약 X 증후군으로 진단되었다. 또한 환자의 어머니에서 30과 98회의 반복 allele을 확인함으로써, 이 환자의 full mutation allele은 모계의 premutation allele로부터 유래한 것임을 알 수 있었다.

결 론: Abbott Molecular Fragile X PCR Kit를 사용한 진단방법은, 취약 X 증후군환자의 경우에서 통상적으로 시행되고 있는 PCR, MS-PCR, Southern blotting을 병행하는 방법에 비해 신속하고 정확한 분자유전학적 진단이 가능한 유용한 방법이라 생각된다.

Purpose: Fragile X syndrome (FXS) is the most common heritable cause of cognitive impairment. FXS is caused by hyperexpansion and hypermethylation of a polymorphic CGG trinucleotide repeat in the 5’ untranslated region of the fragile X mental retadation-1(FMR1) gene. Combination of Southern blotting and simple polymerase chain reaction(PCR) amplification of the FMR1 repeat region is commonly used for diagnosis in females. To give a definite diagnosis in a female child suspected of having FXS, we carried out the molecular diagnostic test for FXS using the recently developed Abbott Molecular Fragile X PCR Kit.

Methods: The PCR amplification of the FMR1 repeat region was performed using the Abbott Mdecular Fragile X PCR Kit. The amplified products were analyzed by size-separate analysis on 1.5% agarose gels and by DNA fragment analysis using Gene scan.

Results: Agarose gel and Gene scan analyses of PCR products of the FMR1 repeat region showed that the patient had two heterozygous alleles with a normal 30 repeats and full mutation of >200 repeats whereas her mother had two heterozygous alleles with the normal 30 repeats and premutation of 108 repeats, suggesting that the premutation of 108 repeats in her mother may have led to the full mutation of >200 repeats in the patient.

Conclusion: We diagnosed FXS in a female patient using a simplified molecular diagnostic test. This commercially available diagnostic test for FXS, based on PCR, may be a suitable alternative or complement method to Southern blot analysis and PCR analysis and/or methylation specific(MS)-PCR analysis for the molecular diagnosis of FXS in both males and females.