Marcel Mannens conducts genetic and epigenetic research on the causes of illness with a view to applying the resulting insights in the field of genome diagnostics. In addition to more classical research on the genetic causes of hereditary diseases, genetic and epigenetic research is focused on environmental influences on gene expression. These influences include factors such as malnutrition, obesity, trauma, stress, child abuse and neglect and alcohol consumption during pregnancy (foetal alcohol syndrome). Epigenetics also play a role in hereditary diseases and cancer. Since epigenetic changes are potentially reversible, the field of epigenetics offers a host of new medical solutions. Epigenetic biomarkers can serve as predictive markers of illness or as new targets for the development of medicines. 

As a clinical genetic laboratory specialist, Mannens has worked at the AMC-UvA since 1985, where he has served as principal researcher since 2007. He was appointed chairman of the Clinical Genetics department in 2011 (a.i.) and head of the AMC-UvA's Genome Diagnostics Laboratory in 2014. As of 2002, he has also worked for the Accreditation Council and for CCKL, the foundation for laboratory research quality assurance. Mannens served in various management capacities within the human genetics and clinical genetics laboratory associations. His research team has published over 170 scientific publications in journals such as The Lancet, Nature Genetics, PNAS and The American Journal of Human Genetics.