5. Just over 99.9% of the observed cases of Rett Syndrome occur in biological women with the sex chromosome arrangement of XX. That means 0.1% of cases occur in biological males, even though we discussed that Rett Syndrome normally leads to in utero death/miscarriage in that population. The 0.1% of cases of Rett Syndrome that occur in men lead to similar symptoms seen in women and at similar ages, so it's not a case where the child is born and dies very early on; they have bona fide Rett Syndrome. Describe a biological mechanism and/or explanation for how men can have Rett Syndrome?