Significantly Elevated FMR1 mRNA and Mosaicism for Methylated Premutation and Full Mutation Alleles in Two Brothers with Autism Features Referred for Fragile X Testing
journal contributionposted on 2022-03-28, 04:13 authored by M Field, T Dudding-Byth, M Arpone, Emma BakerEmma Baker, SM Aliaga, C Rogers, C Hickerton, D Francis, DG Phelan, EE Palmer, DJ Amor, H Slater, L Bretherton, L Ling, DE Godler
Although fragile X syndrome (FXS) is caused by a hypermethylated full mutation (FM) expansion with ≥200 cytosine-guanine-guanine (CGG) repeats, and a decrease in FMR1 mRNA and its protein (FMRP), incomplete silencing has been associated with more severe autism features in FXS males. This study reports on brothers (B1 and B2), aged 5 and 2 years, with autistic features and language delay, but a higher non-verbal IQ in comparison to typical FXS. CGG sizing using AmplideX PCR only identified premutation (PM: 55–199 CGGs) alleles in blood. Similarly, follow-up in B1 only revealed PM alleles in saliva and skin fibroblasts; whereas, an FM expansion was detected in both saliva and buccal DNA of B2. While Southern blot analysis of blood detected an unmethylated FM, methylation analysis with a more sensitive methodology showed that B1 had partially methylated PM alleles in blood and fibroblasts, which were completely unmethylated in buccal and saliva cells. In contrast, B2 was partially methylated in all tested tissues. Moreover, both brothers had FMR1 mRNA ~5 fold higher values than those of controls, FXS and PM cohorts. In conclusion, the presence of unmethylated FM and/or PM in both brothers may lead to an overexpression of toxic expanded mRNA in some cells, which may contribute to neurodevelopmental problems, including elevated autism features.
This work was funded by The Victorian Government's Operational Infrastructure Support Program, Murdoch Children's Research Institute, Royal Children's Hospital Foundation, Martin & E.H. Flack Trust, Pierce Armstrong Trust, Financial Markets Foundation for Children (Australia) (FMFC; grant number: 2017-361), and the National Health and Medical Research Council (NHMRC; project grant numbers: 1049299 and 1103389). D.E.G. was supported by the Next Generation Clinical Researchers Program-Career Development Fellowship Funded by the Medical Research Future Fund (grant number 1141334). M.A. was supported by the International Postgraduate Research Scholarship (IPRS) and the Research Training Program Fee offset scholarship funded by the Australian Government and awarded by the University of Melbourne, and in part by the Diagnosis and Development group of the Murdoch Children's Research Institute.
JournalInternational Journal of Molecular Sciences
PublisherMultidisciplinary Digital Publishing Institute (MDPI)
Rights Statement© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).
Science & TechnologyLife Sciences & BiomedicinePhysical SciencesBiochemistry & Molecular BiologyChemistry, MultidisciplinaryChemistryfragile X syndromeautismRNA toxicityDNA methylationmosaicismpediatricsMS-QMAAmplideXPREMATURE OVARIAN FAILUREHIGH-FUNCTIONING MALEREPEAT EXPANSIONDIRECT DIAGNOSISMALESIDENTIFICATIONPROTEINGENEPHENOTYPECHILDRENAllelesAutistic DisorderChild, PreschoolDNA MethylationFragile X Mental Retardation ProteinFragile X SyndromeHumansMaleMosaicismMutationRNA, MessengerSiblingsUp-RegulationChemical Physics