Hemizygous males will usually be severely affected, while female carriers can have varying symptoms - from unaffected to a similar presentation as an affected male.
The commonly accepted, though unconfirmed, explanation for most of the affected individuals being women is that the non-mosaic hemizygous males are not viable.
According to this model, if an individual is heterozygous for a certain locus, it develops into a female, whereas hemizygous and homozygous individuals develop into males.