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Three patients with ring (X) chromosomes and a severe phenotype
N R Dennis1, A L Collins, J A Crolla
1Wessex Clinical Genetics Service, Princess Anne Hospital, Southampton, UK.
Journal of Medical Genetics
|June 1, 1993
Summary
Ring (X) chromosome mosaicism in three patients presents a severe phenotype, including intellectual disability and limb anomalies, distinct from typical Turner syndrome. This suggests complex genetic mechanisms beyond simple X chromosome inactivation.
Area of Science:
- Genetics
- Human Biology
- Developmental Biology
Background:
- Mosaicism involving ring (X) chromosomes can lead to complex genetic conditions.
- Turner syndrome, typically associated with a 45,X karyotype, presents a spectrum of phenotypes.
- Understanding the genetic basis of severe developmental abnormalities is crucial for diagnosis and management.
Observation:
- Three patients with mosaicism and a small ring (X) chromosome exhibited a severe phenotype.
- Clinical features included mental retardation, distinctive facial features resembling Kabuki syndrome, and limb anomalies.
- Some patients displayed streaky hyperpigmentation, suggesting dermal mosaicism.
Findings:
- The observed phenotype was more severe than typically seen in Turner syndrome.
- The karyotype was often 45,X/46,X,r(X), indicating a mixture of cell populations.
- Evidence against the hypothesis of the small ring (X) chromosome remaining active includes similar phenotypes in 45,X/46,X,r(Y) patients, late replication of some ring (X) chromosomes, and XIST expression.
Implications:
- The severe phenotype associated with ring (X) chromosome mosaicism may result from factors other than simple X chromosome inactivation.
- Further research is needed to elucidate the precise mechanisms underlying these complex genetic disorders.
- Accurate diagnosis and understanding of these conditions are vital for genetic counseling and potential therapeutic strategies.