By law, donors need only screened for sexually transmitted diseases and some communicable diseases.
At the very least, advocates say sperm and egg donors should have "vigorous" face-to-face medical screening and genetic testing for diseases like cystic fibrosis, Tay-Sachs disease, Fragile X syndrome, among others.
Unless donors have a relationship with the child's parent, the donor is anonymous and only has a number. Advocates say that practice should end.
To find a donor, offspring like Tyler have to have a birth date and try to figure it out.
Tyler's mother contacted the California sperm bank she had used to get pregnant, learning John's level of education, degree, and work history. She knew he had lived in Delaware when he went to college.
His work history lined up with an internship program and when she reached them, they provided a public brochure with John's picture.
"It was my son's face," said Blackwell. "They are identical."
When Tyler was 2, doctors thought he had neurofibromatosis and the sperm bank had contacted John to see if anyone in the family had ever had the disease.
"He never responded, and they did not follow-up," said Blackwell. As she later learned from his sister, John has Asperger's syndrome, just like Tyler, a disorder that can make it difficult to initiate social contact.
Eventually, Blackwell found John was living in San Francisco and sent a certified letter but never heard back from him.
But in 2010, John's sister found Blackwell on Ancestry.com and asked why the mother and son had been searching for her brother. She had known John was a sperm donor but thought it was his responsibility to notify the Blackwells. When he didn't, she sent an e-mail explaining the medical history.
"She told me right away she told me about the possibility of Marfan's syndrome," said Blackwell. "John's brother Joe had been diagnosed, without the aortic defect, and his grandmother and brother Bob also had the heart defect."
When a sperm or egg donor develops a genetic disease after donation, the medical history is almost never reported to donor families, according Kramer, who has helped thousands of families share medical information.
One California donor passed on hypertrophic cardiomyopathy to nine of his 22 known offspring and one died, she said. A 3-year-old developed Rasmussen's encephalitis, resulting in seizures and brain damage.
"[John] should never have been a sperm donor," said Kramer. "How could such a thing happen in this era of medical advances and an explosion of genomic information about the causes and inheritance of disease, especially in the most medical advanced country in the world?"
In May, a Supreme Court in British Columbia struck down provincial legislation that protected the identity of sperm donors. The judge also prohibited the future destruction of any records and ordered the province to draw up new legislation, extending the rights of adopted children to donor-conceived children.