Tissue mosaicism, FMR1 expression and intellectual functioning in males with fragile X syndrome

Emma K Baker; Marta Arpone; Minh Bui; Claudine M Kraan; Ling Ling; David Francis; Mathew F Hunter; Carolyn Rogers; Michael J Field; Lorena Santa María; Víctor Faundes; Bianca Curotto; Paulina Morales; Cesar Trigo; Isabel Salas; Angelica M Alliende; David J Amor; David E Godler

doi:10.1002/ajmg.a.63027

Tissue mosaicism, FMR1 expression and intellectual functioning in males with fragile X syndrome

Am J Med Genet A. 2023 Feb;191(2):357-369. doi: 10.1002/ajmg.a.63027. Epub 2022 Nov 8.

Authors

Emma K Baker^{1

2

3}, Marta Arpone^{1

2

4}, Minh Bui⁵, Claudine M Kraan^{1

2}, Ling Ling¹, David Francis⁶, Mathew F Hunter^{7

8}, Carolyn Rogers⁹, Michael J Field⁹, Lorena Santa María¹⁰, Víctor Faundes¹⁰, Bianca Curotto¹⁰, Paulina Morales¹⁰, Cesar Trigo¹⁰, Isabel Salas¹⁰, Angelica M Alliende¹⁰, David J Amor^{2

11}, David E Godler^{1

2}

Affiliations

¹ Diagnosis and Development, Murdoch Children's Research Institute, Royal Children's Hospital, Melbourne, Victoria, Australia.
² Department of Paediatrics, Faculty of Medicine, Dentistry and Health Sciences, University of Melbourne, Parkville, Victoria, Australia.
³ School of Psychology and Public Health, La Trobe University, Bundoora, Victoria, Australia.
⁴ Brain and Mind, Murdoch Children's Research Institute, Royal Children's Hospital, Parkville, Victoria, Australia.
⁵ Centre for Epidemiology and Biostatistics, Melbourne School of Population and Global Health, University of Melbourne, Melbourne, Victoria, Australia.
⁶ Victorian Clinical Genetics Services and Murdoch Children's Research Institute, The Royal Children's Hospital, Melbourne, Victoria, Australia.
⁷ Monash Genetics, Monash Health, Clayton, Victoria, Australia.
⁸ Department of Paediatrics, Monash University, Clayton, Victoria, Australia.
⁹ Genetics of Learning Disability Service, Hunter Genetics, Waratah, New South Wales, Australia.
¹⁰ Molecular and Cytogenetics Laboratory, INTA University of Chile, Santiago, Chile.
¹¹ Neurodisability and Rehabilitation, Murdoch Children's Research Institute, Royal Children's Hospital, Melbourne, Victoria, Australia.

Abstract

Fragile X syndrome (FXS) is caused by hypermethylation of the FMR1 promoter due to the full mutation expansion (full mutation [FM]: CGG ≥ 200 repeats) and silencing of FMR1. Assessment of mosaicism for active-unmethylated alleles has prognostic utility. This study examined relationships between FMR1 methylation in different tissues with FMR1 messenger ribonucleic acid (mRNA) and intellectual functioning in 87 males with FXS (1.89-43.17 years of age). Methylation sensitive Southern blot (mSB) and Methylation Specific-Quantitative Melt Aanalysis (MS-QMA) were used to examine FMR1 methylation. FMR1 mRNA levels in blood showed strong relationships with FMR1 methylation assessed using MS-QMA in blood (n = 68; R² = 0.597; p = 1.4 × 10^-10 ) and buccal epithelial cells (BEC) (n = 62; R² = 0.24; p = 0.003), with these measures also showing relationships with intellectual functioning scores (p < 0.01). However, these relationships were not as strong for mSB, with ~40% of males with only FM alleles that were 100% methylated and non-mosaic by mSB, showing methylation mosaicism by MS-QMA. This was confirmed through presence of detectable levels of FMR1 mRNA in blood. In summary, FMR1 methylation levels in blood and BEC examined by MS-QMA were significantly associated with FMR1 mRNA levels and intellectual functioning in males with FXS. These relationships were not as strong for mSB, which underestimated prevalence of mosaicism.

Keywords: DNA methylation; FMR1; epigenetics; fragile X syndrome; intellectual disability; mosaicism.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

DNA Methylation / genetics
Fragile X Mental Retardation Protein / genetics
Fragile X Syndrome* / diagnosis
Fragile X Syndrome* / genetics
Humans
Male
Mosaicism
Mutation
RNA, Messenger / genetics
RNA, Messenger / metabolism

Substances

Fragile X Mental Retardation Protein
RNA, Messenger
FMR1 protein, human