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Trisomy 20q caused by der (X)t(X;20)(q28;q11.2)
J J Waters1, D S Gourley, D A Aitken
1Department of Medical Genetics, Addenbrooke's Hospital, Cambridge, England.
American Journal of Medical Genetics
|July 1, 1990
Summary
This study reports the first case of pure trisomy 20q in a female child, resulting from a maternal X;20 translocation. Gene dosage studies confirmed trisomy 20q and suggested incomplete X chromosome inactivation.
Area of Science:
- Genetics
- Human Genetics
- Chromosomal Abnormalities
Background:
- Trisomy 20q, a rare chromosomal disorder, is often associated with complex rearrangements involving other chromosomes, complicating phenotypic analysis.
- Understanding the genetic basis of trisomy 20q is crucial for diagnosing and managing affected individuals.
Observation:
- A female infant presented with minor anomalies and developmental delay, exhibiting "pure" trisomy 20q (20q11.2-qter).
- This condition arose from the inheritance of a derivative X chromosome, der(X)t(X;20)(q28;q11.2), from her mother, who was a carrier.
- Red cell gene dosage studies for adenosine deaminase (ADA) confirmed trisomy 20q in the proband.
Findings:
- RBG staining and gene dosage studies indicated incomplete inactivation of the autosomal component of the abnormal X chromosome.
- Unexpectedly, the carrier mother exhibited approximately 50% of normal adenosine deaminase gene expression, suggesting altered gene dosage or regulation.
Implications:
- This case provides a clearer understanding of the phenotype associated with pure trisomy 20q, unconfounded by other autosomal involvement.
- The findings highlight the complex mechanisms of X chromosome inactivation and its potential impact on autosomal gene expression in translocation carriers.
- Further research is warranted to elucidate the precise role of ADA gene dosage and X inactivation patterns in developmental outcomes.