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Fragile X syndrome with FMR1 and FMR2 deletion
S J Moore1, L Strain, G F Cole
1Department of Medical Genetics, Aberdeen Royal Hospitals Trust, Foresterhill, UK.
Journal of Medical Genetics
|July 29, 1999
Summary
A rare deletion of FMR1 and FMR2 genes caused severe developmental delay and epilepsy in a young boy. This finding highlights the importance of genetic testing for fragile X syndrome when standard tests fail.
Area of Science:
- Genetics
- Neurodevelopmental Disorders
- Molecular Biology
Background:
- Fragile X syndrome (FXS) is typically caused by triplet repeat expansions in the FMR1 gene.
- Genetic deletions involving FMR1 and adjacent genes can lead to distinct phenotypes.
Observation:
- A 13-year-old boy presented with severe developmental delay, epilepsy, autistic features, epicanthic folds, and joint hypermobility.
- This patient had a de novo deletion encompassing both FMR1 and FMR2 genes, the smallest reported to date.
- Initial diagnostic tests, including cytogenetics and standard FMR1 molecular tests, were inconclusive.
Findings:
- Comparison with three other reported cases of FMR1 and FMR2 deletion revealed shared features of epilepsy and more severe intellectual disability than typical FXS.
- Three of the four patients exhibited joint laxity, and two had epicanthic folds.
- Severe developmental delay and epilepsy appear to be characteristic of the phenotype resulting from the deletion of both FMR1 and FMR2 genes.
Implications:
- The study suggests that severe developmental delay and epilepsy may be key features of the FMR1/FMR2 deletion syndrome.
- It emphasizes the need for advanced DNA studies to detect deletions in cases of suspected fragile X syndrome where routine testing yields negative results.
- This expands the understanding of the genetic basis and clinical spectrum of fragile X-associated disorders.