X INACTIVATION PATTERNS AND FVIII:C ACTIVITY LEVELS IN FEMALE CARRIERS AND NON-CARRIERS OF SEVERE FACTOR VIII GENE MUTATIONS

PAMELA RADIC; TOMÁS TETZLAFF; CECILIA BADUEL; MIGUEL CANDELA; LILIANA ROSSETTI; CARLOS DE BRASI

Buenos Aires, Argentina

Congreso; XXIX International Congress of the World Federation of Hemophilia; 2010

World Federation of Hemophilia

In mammals, random X-chromosome inactivation of one X in XX females compensates with XY males the existing X-linked gene dose imbalance. It is widely believed that FVIII:C levels from haemophilia A (HA) carriers inversely correlates with the inactivation on the X-chromosome in phase with HA. However, this theoretical correlation remains elusive in practice. This may be due to: (a) impossibility to analyse liver samples (FVIII-secreting tissue), (b) odd chances to phase the tested X-inactivation locus and the F8-mutation and (c) the abundant sources of error and biological variability of FVIII:C. To address this problem we analysed the correlation between FVIII:C and X-inactivation pattern (XIP) on 28 severe-HA carriers and 15 non-carriers (controls) under designed theoretical frameworks. XIP values were calculated from peripheral blood leukocytes using the HUMARA gene system. Heterozygous carriers and non-carrier genotypes were characterised by our algorithm to analyse the entire F8. Carriers showed FVIII:C mean of 45IU/dl (SD: 30IU/dl) and XIP mean of 72% (SD: 15%); and non-carriers FVIII:C mean of 92IU/dl (SD: 23IU/dl) and XIP mean of 65% (SD: 9%). No FVIII:C-XIP correlation of raw data was observed in both carriers and non carriers. To overcome the phase problem (b), an obstacle that masks an eventual correlation, FVIII:C data were transformed (mirrored) and reanalysed. Transformed data showed a modest positive correlation in carriers and complete absence of correlation in non-carriers. These data and the presence of two cases of HA-affected carriers with extremely skewed XIP suggest that the theoretical correlation FVIII:C-XIP might underlie our results although still obscured by the above mentioned impediments.