Our Lady's Crumlin Children's Hospital in Dublin was to review how an adult patient was wrongly told that he did not have a cancer gene.
The patient has been diagnosed with ovarian cancer and is very sick.
This problem involves the Department of Clinical Genetics at the hospital.
RTÉ News has learned that a staff member is on leave from the incident.
Our Lady's Children's Hospital said it could not discuss individual patient cases.
Details of the case have been reported in the newspaper & # 39; The Sunday Times & # 39; Irish edition.
It is understood that blood tests for what are called, genes & # 39; BRACA 1 & # 39; sent by Crumlin for testing at a British hospital in September 2009.
British hospitals report positive tests for genes and tell Crumlin but this is not delivered to patients.
Positive results mean that a patient has a higher risk of breast or ovarian cancer, than someone who does not have a BRACA gene mutation.
Hospital reviews are expected to check how the information was not properly communicated to women by Crumlin.
RTÉ News understands that patients are diagnosed with cancer this year and are undergoing treatment.
Following questions, Crumlin hospital told RTÉ News that it was committed to a culture that promoted an open and positive approach to incident management.
It said the hospital followed the HSE Incident Management Framework in relation to incident reporting.
The hospital said that in July 2018, Crumlin provided additional resources to support the Clinical Genetics Department to improve services.
Crumlin said that an external multi-professional team, led by an experienced health manager working in the UK, had helped the Clinical Genetics Department to provide better services for patients and clinical service users