Repeat expansion and methylation-sensitive triplet-primed polymerase chain reaction for fragile X mental retardation 1 gene screening in institutionalised intellectually disabled individuals.

Nydia Rena Benita Sihombing; Shiwei Cai; Daphne Pei Wen Wong; Ming Guan; Samuel Siong-chuan Chong; Sultana Muhammad Hussein Faradz; Tri Indah Winarni

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Repeat expansion and methylation-sensitive triplet-primed polymerase chain reaction for fragile X mental retardation 1 gene screening in institutionalised intellectually disabled individuals.

Author: Nydia Rena Benita SIHOMBING ¹ ; Shiwei CAI ² ; Daphne Pei Wen WONG ² ; Ming GUAN ² ; Samuel Siong-Chuan CHONG ³ ; Sultana Muhammad Hussein FARADZ ⁴ ; Tri Indah WINARNI ⁴
Author Information

1. Faculty of Medicine, Diponegoro University, Semarang, Indonesia.
2. The BioFactory Pte Ltd, Singapore.
3. Department of Paediatrics, Yong Loo Lin School of Medicine, National University of Singapore, Singapore.
4. Center for Biomedical Research (CEBIOR), Faculty of Medicine, Diponegoro University, Semarang, Indonesia.
Publication Type:Journal Article
Keywords: FMR1 gene screening; Fragile X syndrome; intellectual disability; triple-primed PCR
From:Singapore medical journal 2021;62(3):143-148
CountrySingapore
Language:English
Abstract: INTRODUCTION:Fragile X syndrome (FXS) is the most prevalent X-linked intellectual disability (ID) and a leading genetic cause of autism, characterised by cognitive and behavioural impairments. The hyperexpansion of a CGG repeat in the fragile X mental retardation 1 (FMR1) gene leads to abnormal hypermethylation, resulting in the lack or absence of its protein. Tools for establishing the diagnosis of FXS have been extensively developed, including assays based on triplet-primed polymerase chain reaction (TP-PCR) for detection and quantification of the CGG trinucleotide repeat expansion, as well as determination of the methylation status of the alleles. This study aimed to utilise a simple, quick and affordable method for high sensitivity and specificity screening and diagnosis of FXS in institutionalised individuals with ID.
METHODS:A total of 109 institutionalised individuals at the Center for Social Rehabilitation of Intellectual Disability Kartini, Temanggung, Central Java, Indonesia, were screened in a three-step process using FastFrax™ Identification, Sizing and Methylation Status Kits.
RESULTS:Two samples that were classified as indeterminate with respect to the 41-repeat control at the identification step were subsequently determined to be non-expanded by both sizing and methylation status analyses. Two samples classified as expanded at the identification step were determined to carry full mutation expansions > 200 repeats that were fully methylated using sizing and methylation status analyses, respectively, yielding a disease prevalence of 1.83%.
CONCLUSION:Repeat expansion and methylation-specific TP-PCR is practical, effective and inexpensive for the diagnosis of FXS, especially in high-risk populations of individuals with ID of undetermined aetiology.