Haemophilia 'A' in a 46,X,i(Xq) female.

A phenotypically normal female, with negative family history for bleeding disorders, was found to be affected by severe haemophilia A. All laboratory tests performed confirmed the diagnosis. Chromosome analysis showed the presence of an X isochromosome of the long arm in every cell. It is hypothesized that the propositus inherited the affected X from her mother, a probable carrier, and the isochromosome, of paternal origin, was not able to mask the abnormal gene.