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Skewed X chromosome inactivation and breast and ovarian cancer status: Evidence for X-linked modifiers of BRCA1
Journal article   Peer reviewed

Skewed X chromosome inactivation and breast and ovarian cancer status: Evidence for X-linked modifiers of BRCA1

Felicity Lose, D L Duffy, G F Kay, M A Kedda and A B Spurdle
Journal of the National Cancer Institute, Vol.100(21), pp.1519-1529
2008
DOI: https://doi.org/10.1093/jnci/djn345
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https://doi.org/10.1093/jnci/djn345View
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Abstract

Background: X chromosome inactivation, which silences gene expression from one of the two X chromosomes in females, is usually random. Skewed X inactivation has been implicated in both the expression and the suppression of X-linked disease phenotypes and has been reported to occur more frequently in breast and ovarian cancer patients, including BRCA1 or BRCA2 mutation carriers, than in control subjects. Methods: We assessed the pattern of X chromosome inactivation using methylation-specific polymerase chain reaction amplification of the exon 1 microsatellite region of the X-linked androgen receptor (AR) gene in DNA from blood samples obtained from control subjects without a personal history of breast or ovarian cancer (n = 735), ovarian cancer patients (n = 313), familial breast cancer patients who did not carry mutations in BRCA1 or BRCA2 (n = 235), and affected and unaffected carriers of mutations in BRCA1 (n = 260) or BRCA2 (n = 63). We defined the pattern of X chromosome inactivation as skewed when the same X chromosome was active in at least 90% of cells. The association between skewed X inactivation and disease and/or BRCA mutation status was assessed by logistic regression analysis. The association between skewed X inactivation and age at cancer diagnosis was assessed by Cox proportional hazards regression analysis. All statistical tests were two-sided. Results: The age-adjusted frequency of skewed X inactivation was not statistically significantly higher in ovarian cancer or familial breast cancer case subjects compared with control subjects. Skewed X inactivation was higher in BRCA1 mutation carriers than in control subjects (odds ratio [OR] = 2.7, 95% confidence interval [CI] = 1.1 to 6.2; P =. 02), particularly among unaffected women (OR = 6.1, 95% CI = 1.5 to 31.8; P =. 005). Among BRCA1 mutation carriers, those with skewed X inactivation were older at diagnosis of breast or ovarian cancer than those without skewed X inactivation (hazard ratio [HR] of breast or ovarian cancer = 0.37, 95% CI = 0.14 to 0.95; P =. 04). Among BRCA2 mutation carriers, skewed X inactivation also occurred more frequently in unaffected carriers than in those diagnosed with breast or ovarian cancer (OR = 5.2, 95% CI = 0.5 to 28.9; P =. 08) and was associated with delayed age at onset (HR = 0.59, 95% CI = 0.37 to 0.94; P =. 03). Conclusions: Skewed X inactivation occurs at an increased frequency in BRCA1 (and possibly BRCA2) mutation carriers compared with control subjects and is associated with a statistically significant increase in age at diagnosis of breast and ovarian cancer. © The Author 2008. Published by Oxford University Press.

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