About one third of new cases are caused by a new mutation of the gene in the mother or the child. In these cases, there is no previous history of hemophilia in the family.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/shocking-80-percent-hemophilia-cases-undiagnosed-india-say-health-experts
[2] http://admin.indiaenvironmentportal.org.in/category/newspaper/financial-express-new-delhi
[3] http://admin.indiaenvironmentportal.org.in/category/thesaurus/health
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/health-effects
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/medical-research