A sperm donation scandal disclosed recently has aroused growing concern in the United States.According to the New York Times\' report, Ryan Kramer, the son of a donor, found that he has more than 150 half-siblings - they are all the children of the same donor. \"It\'s wild when we see them all together - they all look alike,\" said Cynthia Daily, mother of Kramer.As more women choose to have children on their own, the demand for sperm donors has surged.Some sperm banks are earning huge profits by allowing too many mothers to receive sperms from the same popular donors, according to the report. And this trend will lead to risks: rare genetic diseases could be spread more widely, and the children of the same donor could meet and, unbeknownst to them, commit incest, medical experts warned. Parents and donors are calling for a tighter regulation so that donor children can know more about their donors, and the number of kids from each donor can be limited.