Hideaki Kato discovered his true identity by accident. During his medical training a decade ago, the now 39-year-old Japanese doctor was performing blood tests on family members when he learned something startling: his dad was not his biological father.
Suspecting an extramarital affair, the Tokyo-area physician questioned his mother while the man he had always known as his father was away on a trip.
But rather than uncovering a cheating parent, Kato learned his biological father was an anonymous sperm donor and that his parents had hidden the infertility from him.
"I felt as if half of me had collapsed," he said.
"I asked myself 'were childhood memories of my family's smiling faces at the beach just a fake?'"
But Kato's desire to learn more was hampered by his upset parents and a lack of laws in Japan over access to details of his genetic parentage.
It is a challenge shared by thousands of people in Japan and elsewhere who were the product of anonymous sperm and egg donors.
Many suffer identity crises upon learning of their background and wonder about the existence of a brother or sister, or fear unwittingly forming a romantic relationship with a half-sibling.
Such concerns have led many donor-conceived children to call for the practice to be banned, among them a 33-year-old editor at a Tokyo publishing company.
Ten years ago, the woman dropped out of university, distraught after being told her father was not biologically related to her.
"I hope (it) will be banned," she said, referring to anonymous donors.
"Why isn't adoption enough? To me, the technology is a way to pretend that you have a 'normal family', to hide infertility in a society where the pressure is still high to get married and have children."
She added that treatment with donor eggs was another worrying technology.
"I don't want children of donor eggs to suffer the same mental anguish that I experienced," she said.
She is far from alone.
Canadian Olivia Pratten filed a lawsuit to learn her genetic identity, and in 2011 the British Columbia Supreme Court ruled donor-conceived children in the province should be guaranteed access to their biological parents' identities.
That ruling was overturned in November 2012 on appeal, but Pratten may take the case to the country's top court, according to Canadian media reports.
She rejects arguments that lifting anonymity would all but empty the pool of willing donors.
"The fertility industry likes to falsely claim that no anonymity equals no donors. This is absolutely false," Pratten said in an email to AFP.
"Other countries, from New Zealand to Sweden to the United Kingdom to certain states in Australia have successfully banned anonymity," she added.
In 2005, Britain changed the law so donor-conceived people could learn the identity of their parents, according to the country's National Health Service.
Elsewhere, there is a patchwork of anonymity laws, or no relevant legislation at all including in Japan, which also has no regulations for doctors carrying out the procedure.
"It is more complex and less cost-effective to run an open system, but the rights and needs of the resulting children must be kept paramount," Pratten said.
"I am sympathetic to those facing infertility, but the desire to have genetic lineage needs to be respected for both the parents and children."
For his part, Kato's efforts to learn his father's identity included getting a list of medical school graduates at Japan's Keio University—where his parents had sought treatment.
The graduates were potential sperm donors, but Kato's decision to pay them a visit in his quest to learn more drew a bewildered reaction from the men.
Yahiro Netsu, whose maternity clinic pioneered fertility treatment with donor eggs in Japan, said he cannot ignore patients' desire to have children.
"If a child born from a donor egg faces an identity crisis, it will eventually ease if there is trust between the child and the parents," Netsu said.
But he agreed children should have the right to know their genetic history.
Mari Saimura, a professor at Tezukayama University, is among those who are calling for Japan to establish laws on the issue.
"Japan should give up the technology unless it sets up guidelines to guarantee people's right to know their identity," Saimura said.
There has been little progress on the issue in Japan since a decade-old government report recommended rules guaranteeing information about donor parents and notifying children of their parentage early on, she said.
For Kato, his paternal roots remain a mystery.
"I've never forgotten about my biological father. I always carry a list of potential donors, which is a sort of talisman to me," he said.
"But I don't want my biological father to become my 'father.' I just want to know my genetic origin."