Several genetic diseases may be the result of splice site mutations. For example, mutations that cause the incorrect splicing of β-globin mRNA are responsible of some cases of β-thalassemia. Another Example is TTP (thrombotic thrombocytopenic purpura). TTP is caused by deficiency of ADAMTS-13. A splice site mutation of ADAMTS-13 gene can therefore cause TTP. It is estimated that 15% of all point mutations causing human genetic diseases occur within a splice site.