Towards a Better Molecular Diagnosis of FMR1-Related Disorders—A Multiyear Experience from a Reference Lab

Sylwia Rzońca,Agnieszka Szpecht-Potocka,Anna Abramowicz,Monika Gos,Jerzy Bal,Aleksandra Landowska,Danuta Sielska-Rotblum,Michał Milewski,Tadeusz Mazurczak,Ewa Obersztyn,Dorota Maciejko,Daniel Szopa,Jolanta Czekajska

doi:10.3390/genes7090059

Abstract

The article summarizes over 20 years of experience of a reference lab in fragile X mental retardation 1 gene (FMR1) molecular analysis in the molecular diagnosis of fragile X spectrum disorders. This includes fragile X syndrome (FXS), fragile X-associated primary ovarian insufficiency (FXPOI) and fragile X-associated tremor/ataxia syndrome (FXTAS), which are three different clinical conditions with the same molecular background. They are all associated with an expansion of CGG repeats in the 5′UTR of FMR1 gene. Until 2016, the FMR1 gene was tested in 9185 individuals with the pre-screening PCR, supplemented with Southern blot analysis and/or Triplet Repeat Primed PCR based method. This approach allowed us to confirm the diagnosis of FXS, FXPOI FXTAS in 636/9131 (6.96%), 4/43 (9.3%) and 3/11 (27.3%) of the studied cases, respectively. Moreover, the FXS carrier status was established in 389 individuals. The technical aspect of the molecular analysis is very important in diagnosis of FXS-related disorders. The new methods were subsequently implemented in our laboratory. This allowed the significance of the Southern blot technique to be decreased until its complete withdrawal. Our experience points out the necessity of implementation of the GeneScan based methods to simplify the testing procedure as well as to obtain more information for the patient, especially if TP-PCR based methods are used.

Highlights

The fragile X mental retardation gene (FMR1) is localized on chromosome X (Xq27.3).An expansion of the CGG repeat in 50 UTR region of the fragile X mental retardation 1 gene (FMR1) gene may cause three different clinicalGenes 2016, 7, 59; doi:10.3390/genes7090059 www.mdpi.com/journal/genesGenes 2016, 7, 59 conditions: fragile X syndrome, fragile X-associated primary ovarian insufficiency (FXPOI) and fragile X-associated tremor/ataxia syndrome (FXTAS; in both number of CGG repeats within range 55–200).Fragile X syndrome (FXS) is the most common inherited form of intellectual disability (ID), with a population prevalence of about 1/4000–9000 males and 1/7000–15,000 females [1,2,3]
The clinical diagnosis of FXS was confirmed by Southern blot hybridization and/or the TP-PCR
The GeneScan method significantly reduced the cost and time required for the FXS molecular testing

Summary

Introduction

The fragile X mental retardation gene (FMR1) is localized on chromosome X (Xq27.3).An expansion of the CGG repeat in 50 UTR region of the FMR1 gene may cause three different clinicalGenes 2016, 7, 59; doi:10.3390/genes7090059 www.mdpi.com/journal/genesGenes 2016, 7, 59 conditions: fragile X syndrome (number of CGG repeats over 200), fragile X-associated primary ovarian insufficiency (FXPOI) and fragile X-associated tremor/ataxia syndrome (FXTAS; in both number of CGG repeats within range 55–200).Fragile X syndrome (FXS) is the most common inherited form of intellectual disability (ID), with a population prevalence of about 1/4000–9000 males and 1/7000–15,000 females [1,2,3]. The fragile X mental retardation gene (FMR1) is localized on chromosome X (Xq27.3). An expansion of the CGG repeat in 50 UTR region of the FMR1 gene may cause three different clinical. Fragile X syndrome (FXS) is the most common inherited form of intellectual disability (ID), with a population prevalence of about 1/4000–9000 males and 1/7000–15,000 females [1,2,3]. Though the severity and clinical manifestation of the disease vary, FXS has several characteristic symptoms: intellectual impairment (mild to moderate), which may be accompanied by specific dysmorphic features like long face, large prominent ears, large jaw, and macroorchidism. The majority of FXS cases (>99%) are caused by the significant expansion of CGG trinucleotide repeats over 200, termed a “full mutation”, associated with methylation of the promoter and 50 UTR regions of the FMR1 gene. The pronounced methylation leads to decrease of the expression of FMR1

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Conclusion