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Discordant phenotypes and 45,X/46,X,idic(Y)
T E Kelly1, J B Franko, A Rogol
1Division of Medical Genetics, University of Virginia School of Medicine, Charlottesville, USA.
Journal of Medical Genetics
|October 23, 1998
Summary
Mosaicism causes varied clinical outcomes in chromosomal abnormalities. Identical karyotypes in Turner syndrome and mixed gonadal dysgenesis patients highlight the role of SRY and ZFY gene expression in determining phenotype.
Area of Science:
- Genetics
- Developmental Biology
- Endocrinology
Background:
- Mosaicism, the presence of two or more cell lines with different karyotypes, leads to diverse clinical presentations in chromosomal abnormalities.
- The 45,X/46,XY karyotype is associated with a spectrum of conditions, including Turner syndrome, mixed gonadal dysgenesis, and normal male development.
- Phenotypic variability is largely influenced by the chromosomal makeup of the developing gonad.
Observation:
- This study examined two patients with identical karyotypes: 45,X/46,X,idic(Y)(p11.2).
- One patient presented with Turner syndrome, while the other exhibited mixed gonadal dysgenesis.
- Polymerase chain reaction (PCR) analysis revealed differences in SRY and ZFY gene presence.
Findings:
- The Turner syndrome patient was negative for both SRY and ZFY genes.
- The mixed gonadal dysgenesis patient was positive for both SRY and ZFY genes.
- Despite identical karyotypes, the presence or absence of key Y-chromosome genes (SRY, ZFY) determined the distinct phenotypes.
Implications:
- This case underscores that mosaicism alone may not fully explain phenotypic variability.
- The expression of specific Y-chromosome genes, such as SRY and ZFY, is critical in determining gonadal development and subsequent clinical phenotype.
- Understanding gene expression in mosaic conditions is vital for accurate diagnosis and genetic counseling.