'Entire identity is built on a lie': Fertility clinic doctor told woman sperm donor was 'anonymous medical student' — but he was actually the biological father, lawsuit says

Joseph Laedtke Heider (WISN).

A Wisconsin fertility doctor duped a woman into thinking her sperm donor was a young medical student when the donor was in fact the doctor himself, a lawsuit alleges.

Mary Ellen Lukezich and her son, Joseph Laedtke Heider, are suing Dr. Frederick Dettmann in Milwaukee Circuit Court.

Now in his 40s, Heider made the discovery in 2024 when he submitted his DNA to Ancestry.com and discovered Dettmann was his biological father, according to the lawsuit obtained by local ABC affiliate WISN.

Lukezich was a patient at Dettmann's clinic in the early 1980s. Per the plaintiffs, Dettmann told Lukezich that the donor was a "healthy young medical student" who wished to remain anonymous.

But that proved to be a lie, Heider said.

"The anonymous medical student donor that my mother was promised as my biological father never existed. Instead, the DNA led back to one person. Dr. Frederick Dettmann, the very doctor my mom trusted to help her have a child," Heider said at a press conference attended by WISN in June. "Words cannot fully express what it feels like to learn that your entire identity is built on a lie."

Attorney Al Foeckler on Thursday filed the lawsuit against Dettmann on behalf of Heider and Lukezich. The Wisconsin Health Care Liability Insurance Plan and ABC Insurance Co. are also listed as defendants, records show.

"These families come to fertility doctors at their most hopeful and their most helpless time. Trusting completely in the physician who holds their dreams of parenthood in their hands," Foeckler told reporters. "Dr. Frederick Dettmann preyed on that desperation. He exploited that trust."

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Dettmann has since retired and is now 91. In a statement from his lawyers to local media, he denied any wrongdoing.

"The events referenced are alleged to have occurred almost 50 years ago," the statement said. "Dr. Dettmann has no independent recollection of the individuals making these allegations and is unaware of any evidence supporting the claims being asserted."