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Psychiatric and Cognitive Features in Italian Women With the FMR1 Premutation: A Comprehensive Assessment Using SCID-5 and Standardized Cognitive Measures.

American journal of medical genetics. Part B, Neuropsychiatric genetics : the official publication of the International Society of Psychiatric Genetics·2026
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Progression of fragile X-associated tremor/ataxia syndrome revealed by subtype and stage inference.

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Intron 1 of the <i>C9orf72</i> gene: The RNA that RAN.

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A Robust Polymerase Chain Reaction-based Assay for Quantifying Cytosine-guanine-guanine Trinucleotide Repeats in Fragile X Mental Retardation-1 Gene
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Unmethylated Mosaic Full Mutation Males without Fragile X Syndrome.

YeEun Tak1,2, Andrea Schneider2,3, Ellery Santos1

  • 1Medical Investigation of Neurodevelopmental Disorders (MIND) Institute, University of California Davis, Sacramento, CA 95616, USA.

Genes
|March 28, 2024
PubMed
Summary

Individuals with unmethylated Fragile X syndrome (FXS) full mutation (FM) alleles may not exhibit typical cognitive or behavioral deficits. This presentation is rare and may be linked to FMR1 protein production, but carries a risk for Fragile X-associated tremor/ataxia syndrome (FXTAS).

Keywords:
fragile X mosaicismfragile X premutationfragile X premutation-associated conditionsfragile X syndromeunmethylated full mutation

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Area of Science:

  • Genetics
  • Neuroscience
  • Developmental Biology

Background:

  • Fragile X syndrome (FXS), the primary inherited cause of intellectual disability and a major genetic cause of autism, is typically associated with methylation of the FMR1 gene.
  • While most FXS patients with a full mutation (FM) exhibit gene methylation, some present with mosaicism or unmethylated alleles, a rare phenotype with limited research on cognitive and behavioral outcomes.

Observation:

  • This study reviewed literature on individuals with unmethylated and mosaic FMR1 FM alleles.
  • Three male patients with unmethylated FMR1 FM alleles were identified, who presented without any cognitive or behavioral deficits.

Findings:

  • The absence of typical FXS phenotypes in these individuals is unusual, as many with unmethylated FM alleles and no behavioral issues are not diagnosed with FXS.
  • The findings suggest that mosaic males with unmethylated FMR1 FM alleles may not display behavioral phenotypes due to the production of the FMR1 protein (FMRP) from smaller alleles.

Implications:

  • These individuals, despite lacking overt FXS symptoms, may face an elevated risk of developing fragile X-associated tremor/ataxia syndrome (FXTAS) due to increased mRNA expression.
  • Further research is needed to understand the long-term health implications and genetic mechanisms in individuals with unmethylated FMR1 FM alleles.