Investigators are calling on patients treated at a Leiden fertility clinic to get in touch after it emerged a lab worker who illegally donated sperm between 1979 and 1984  had a hereditary condition.

The case started in 2017 when DNA analysis showed that two people found they were related and that their father was a lab worker at the commercial fertility treatment centre SMCG in Leiden.

In 2023 another two children found that, contrary to the clinic’s notes, they were not related and that one of them had been fathered by the lab worker. He is thought to have fathered at least 11 children.

The man subsequently admitted he had been donating sperm under another name but has since refused to cooperate in an investigation by the current owner of the clinic, Medisch Centrum Kinderwens (MCK).

“The SMCG archives are complete but are not always reliable,” director Arne van Heusden told Omroep West.

Van Heusden called on former patients and workers at the clinic to get in touch. It is particularly important they do so because the lab worker was found to have a hereditary condition.

“It is not a life-threatening condition but one that can be passed on in 50% of cases. People simply have the right to know,” he told the broadcaster.

The case is the last in a series of scandals in which gynecologists used their own sperm in fertility treatments.

Fertility doctor Jan Karbaat, in the first case to come to light in 2019, is thought to have fathered some 80 children.