Gil Bellis
INED researcher Gil Bellis studies population genetics and the demography of genetic diseases, together with the issues of vulnerable populations and demographic crises. We asked him about his research in connection with genetic diseases, and cystic fibrosis in particular.
(Interview conducted in January 2024)
What does it mean to study genetic diseases from a demographic perspective?
Studying a group of people with a particular genetic disease involves studying that group in terms of numbers, structure, composition, and all determinants involved in group reconstitution or renewal; i.e., the events involved in “entering” and exiting the disease.
Cystic fibrosis is what’s called a rare disease, meaning a disease that concerns one in 2,000 people; approximately 7,000 such diseases have been identified. One of their particularities is that for a long time little was known about them, making it difficult to diagnose them. In terms of demography, the main difficulty for some rare diseases is arriving at a complete count of all cases.
In addition to specific medical problems, these pathologies can restrict a person’s activities and cause disabilities that in turn impact their academic, occupational, and social situations. All of those being situations are of interest to demographers.
What tools had to be devised in order for demographers to research those questions?
In the early 1990s, parents of children with cystic fibrosis—a disease that affects several organs at once, and one of the most serious rare diseases for children in that it poses major challenges for pediatric care—banded together with relevant institutions for the purpose of counting and keeping track of all persons with the disease and characterizing how they lived. INED helped set up an information system that also served to register all cases of cystic fibrosis in mainland France, Guadeloupe, Martinique, and Reunion. In 1992, the Registre Français de la Mucoviscidose or French cystic fibrosis registry was created. It was run by INSERM through 1998. INED took over in 1999 and gradually delegated management to an association called Vaincre la Mucoviscidose [Defeat cystic fibrosis]. The Registry is credited with accounting for approximately 95% of all cases in France; in 2022, that came close to 7,750 patients.
Systematic neonatal screening for cystic fibrosis was instituted in France in 2002-2003, enabling health professionals to provide immediate treatment to persons born with the disease and to identify and monitor signs of worsening health. This in turn improved patients life expectancy and quality of life. Moreover, treatment strategy was improving considerably over time. In the last forty years, the life expectancy of cystic fibrosis patients has risen from 20-25 to over 51. The adult population has also changed over the years—in 2022, 63% of cystic fibrosis patients were 18 years of age or older—leading to new issues, such as the appearance of adult co-morbidities and the difficulty of working or having a steady occupational life for people with the disease.
What has the Registry and other tools taught researchers?
Since 1992, the Registry has made it possible to keep track of people born with cystic fibrosis and record all of their health events. That in turn enables me, as a demographer, to observes changes in the French cystic fibrosis population and its age structure (this is a hereditary disease that affects the two sexes in equal proportions). From 2017 to 2019, we conducted a survey called “Cystic fibrosis, family, and society” to explore these patients’ living conditions and collect their life trajectories. It covered five dimensions: schooling, occupation, the family, housing, and quality of life; slightly over 450 patients responded. The survey was conducted in collaboration with cystic fibrosis associations, hospitals, and INED’s Surveys Service. One finding was that for students, the disease and the constraints associated with medical treatment of it lead to frequent repeating of school years; adult occupational trajectories were likewise marked by frequent interruptions, some of them fairly long.
In what ways is your work useful to policy and decision makers and public authorities in general?
The French Cystic Fibrosis Registry, together with our survey, can be used to anticipate future patient needs in terms of numbers and treatment. The increased size of the adult cystic fibrosis population means specific in-hospital treatments need to be planned for, as well as space in nursing care facilities for older CF patients. Furthermore, the actions made possible by the Registry—exhaustive case-tracking, specific surveys, etc.—could also be undertaken in connection with other genetic diseases.
