On 11 March, science lost an inspiring leader with the death of Leena Peltonen-Palotie, at the age of 57, following a two-year battle with bone cancer.

Known to those in the field as Leena Peltonen (she was married to her close collaborator Aarno Palotie), she was a key player in human molecular genetics. This was true both in the early days of identifying the genes and mechanisms underlying rare diseases, and more recently in trying to track the causes of common inherited disorders. Peltonen left an invaluable legacy to medical genetics by authoring more than 600 papers and mentoring some 70 PhD students. But perhaps her most enduring contribution was to show how understanding the causes of genetic diseases in isolated populations can offer clues for large-scale studies that probe the risk factors linked to common diseases such as diabetes, obesity and heart disease.

Peltonen completed her PhD at the University of Oulu in Finland in 1978. After postdoctoral work at Rutgers University in New Jersey, she returned to the National Public Health Institute in Helsinki, becoming a professor in 1991.

In the first half of her career, Peltonen's main focus was the diseases that comprise the Finnish Disease Heritage. This is a group of about 40 rare recessive diseases — including metabolic, skin and eye disorders — that are more prevalent in Finland than anywhere else in the world. This prevalence is due to Finland's unusual demographic history: 2,000 years ago, “the edge of the inhabitable world”, as Peltonen put it, was populated by relatively small groups of settlers who carried a limited set of mutations.

Peltonen identified the genes and mechanisms responsible for two dozen of these diseases, and helped find the factors underlying the rest. Her work has allowed physicians around the world to screen and counsel individuals — although ironically, and to her disappointment, Finland itself still lacks a screening programme.

Peltonen's vision and flamboyance, and her ability to raise and employ public awareness about the Finnish Disease Heritage, has helped to transform Finland into one of the most advanced places in the world for human medical genetics. In recognition of this, she was appointed Finnish Academy professor in 2003 and awarded the title Academician of Science in 2009.

During the 1990s, the advent of powerful tools in molecular genetics enabled researchers to home in on the genetics of common diseases that cluster in families. Peltonen's team was at the forefront of this fresh wave of research, identifying an osteoarthritis gene in 1989. But as the hunt for risk factors ramped up, geneticists became engaged in a fierce debate over whether isolated inbred populations held clues to the factors responsible for common diseases. Although she was convinced that they did, Peltonen hedged her bets and stepped up her involvement in worldwide biobank studies in outbred populations, while continuing to pursue her work on isolated populations. In 2002, she united the registries for data on twins in eight European countries to form the GenomEUtwin project. This was the first integrated project to be funded by the European Union (EU), kick-starting European involvement in large-scale genetics. Her push for integration went further in 2003 when the backers of GenomEUtwin, the Canadian CARTaGENE biobank and the Estonian biobank founded P3G, the Public Population Project in Genomics, which unites the data of more than a dozen large biobanks worldwide.

In 2007, Peltonen initiated the unification of most of the European biobanks within the overarching Biobanking and Biomolecular Resources Research Infrastructure (BBMRI). This has been a great success, and now has 52 participants and 150 associated members. Finally, based on the achievements of genome-wide association studies — which involve scanning markers in the genomes of many people to find variations associated with specific diseases — Peltonen, along with Mark McCarthy of the Wellcome Trust Centre for Human Genetics in Oxford, UK, started an EU consortium called ENGAGE in 2007. This collated genome-wide data from 100,000 individuals. As a way of connecting researchers with existing data it was hugely successful, yielding many high-profile papers in just a few months.

Ultimately, Peltonen's parallel pursuit of genetic studies in isolated populations proved prescient. The enrichment of a limited set of mutations yields a simpler picture than that obtained from the larger-scale hunts for the factors underlying complex diseases. Yet some of the components unearthed from the smaller studies, such as the disrupted gene underlying osteoarthritis, have been found to be involved in complex forms of the same disorders.

Peltonen's interest in complex genetics always went beyond merely mapping genes. In 2002, her team unravelled the mechanism of lactose intolerance. Then in 2004 and 2005, her group found the link between a variant of a gene called USF1, which causes a lipid disorder that clusters in families, and insulin resistance. She was particularly proud of these findings, as in both cases the variant genes altered regulatory functions. This suggested a fundamental mechanistic difference between the basic genetic defects typical of Mendelian disease and the more subtle regulatory alterations underlying complex disease.

An outspoken voice on European science policy in Brussels and elsewhere, and a member of the European Research Council, Peltonen was also a world citizen. She received prominent international honours and alternated her career in Finland with missions abroad. She founded and led the Department of Human Genetics at the University of California, Los Angeles, during 1998–2002, was a visiting professor at the Broad Institute in Cambridge, Massachusetts, from 2005 and became head of human genetics at the Wellcome Trust Sanger Institute in Cambridge, UK, in 2007.

Leena Peltonen's drive, radiance and inimitable style were as impressive as her achievements. Few will forget how attendees at a Helsinki meeting were treated to a black conference bag with white polka dots, or how this brightly dressed, chic lady could kick off her high heels and mount a chair to address the troops. Nor will they forget her fortitude as she maintained her unique blend of humour and no-nonsense attitude during her battle with cancer — continuing to lead meetings, guide students and juggle telephone conferences. It is up to us to make good on her legacy, by pursuing not only fame and fortune, but also real clinical utility.