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We report a female infant born to a mother with incontinentia pigmenti (IP) and a father with haemophilia A, who manifests both disorders. Analysis of peripheral blood DNA from the infant, her mother, and two female relatives with IP showed a highly skewed pattern of X inactivation. Random patterns were observed in the infant's two sisters, who do not have IP and have normal carrier activity of factor VIII. Preferential inactivation of the X chromosome bearing the IP mutation, probably by negative selection, appears to have unmasked the factor VIII mutation on the infant's other X chromosome. This illustrates an unusual mechanism for the manifestation of an X linked disease in a heterozygous female.

Original publication




Journal article


J Med Genet

Publication Date





497 - 500


Dosage Compensation, Genetic, Factor VIII, Family Health, Female, Genetic Carrier Screening, Hemophilia A, Heterozygote, Humans, Incontinentia Pigmenti, Infant, Pedigree