Atypical X-chromosome inactivation in an X;1 translocation patient demonstrating Xq28 functional disomy.
X-chromosome inactivation (XCI) is an epigenetic process used to regulate gene dosage in mammalian females by silencing genes on one X-chromosome. While the pattern of XCI is typically random in normal females, abnormalities of the X-chromosome may result in skewing due to disadvantaged cell growth. We describe a female patient with an X;1 translocation [46,X,t(X;1)(q28;q21)] and unusual pattern of XCI who demonstrates functional disomy of the Xq28 region distal to the translocation breakpoint. There was complete skewing of XCI in the patient, along with the atypical findings of an active normal X chromosome and an inactive derivative X. Characterization of the translocation revealed that the patient's Xq28 breakpoint interrupts the DKC1 gene. Molecular analysis of the breakpoint region revealed functional disomy of Xq28 genes distal to DKC1. We propose that atypical XCI occurred in the patient due to a post-inactivation cell selection mechanism likely initiated by disruption of DKC1. As a result, the pattern of XCI is opposite that of the expected for an X;autosome translocation. Therefore, we suggest the phenotypic abnormalities found in the patient are a result of functional disomy in the Xq28 region.
Cottrell
Catherine E
CE
Nationwide Children's Hospital, Columbus, Ohio 43205, USA.
Sommer
Annemarie
A
Wenger
Gail D
GD
Bullard
Steven
S
Busch
Tamara
T
Krahn
Katherine Nash
KN
Lidral
Andrew C
AC
Gastier-Foster
Julie M
JM
D000015:Abnormalities, Multiple / Q000235:genetics; D018797:Cell Cycle Proteins / Q000235:genetics; D019457:Chromosome Breakage; D002874:Chromosome Mapping; D022202:Chromosomes, Artificial, Bacterial; D041321:Chromosomes, Human, X; D018076:DNA, Complementary; D004303:Dosage Compensation, Genetic; D005260:Female; D018628:Gene Dosage; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D009687:Nuclear Proteins / Q000235:genetics; D020411:Oligonucleotide Array Sequence Analysis; D014178:Translocation, Genetic; D024182:Uniparental Disomy / Q000235:genetics*; D049951:X Chromosome Inactivation
D018797:Cell Cycle Proteins; C112148:DKC1 protein, human; D018076:DNA, Complementary; D009687:Nuclear Proteins