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Phenotype and X inactivation in 45,X/46,X,r(X) cases
Kathleen A Leppig1, Virginia P Sybert, Judith L Ross
1Genetic Services, Group Health Permanente, Seattle, Washington 98112, USA. leppig.k@ghc.org
American Journal of Medical Genetics. Part A
|June 25, 2004
Summary
Ring X chromosome (r(X)) presence doesn't solely explain mental retardation. XIST presence and methylation patterns, not just r(X) size, influence inactivation and phenotype in these genetic conditions.
Area of Science:
- Genetics
- Molecular Biology
- Developmental Biology
Background:
- Ring X chromosome (r(X)) is a rare chromosomal abnormality.
- X inactivation is crucial for dosage compensation in females.
- The role of r(X) in phenotypic variation, including mental retardation, requires further investigation.
Observation:
- Studied 21 individuals with mosaic ring X chromosome (r(X)).
- Assessed XIST expression, replication timing, and androgen receptor (AR) gene methylation.
- Correlated r(X) characteristics with intellectual disability and Turner syndrome features.
Findings:
- XIST presence and AR methylation indicate r(X) inactivation in individuals without mental retardation.
- Conflicting results on replication timing and methylation suggest incomplete X inactivation in some cases with r(X) and mental retardation.
- Smaller r(X) size in individuals with mental retardation may hinder complete inactivation.
Implications:
- Phenotypic variability in r(X) mosaicism is complex and not solely determined by XIST.
- Potential dissociation between late replication and DNA methylation in r(X) inactivation.
- Ascertainment bias may influence reported frequencies of abnormalities in r(X) cases.