Ring X chromosome – r(X)

Epidemiology and Etiology:

• 15% of Turner syndrome patients
• Usually in mosaic with 45,X
• May be of maternal or paternal origin

Common sites:

Gross features:

• Lack lymphedema often

Histologic features:

Immunophenotype:

Marker:

Sensitivity:

Specificity:

Molecular features:

• FISH to confirm the ring is of X and not of Y

Other features:

• Some have typical features of Turner
• Others have a severe phenotype with mental retardation, facial dysmorphism, and congenital malformations
• May be those with XIST deleted
• The size of the ring lacking XIST determines the degree of clinical severity
• Might not be possible to accurately predict the phenotype prenatally

References:

· Gersen SL, Keagle MB, eds. The Principles of Clinical Cytogenetics (2005).