While growing up in the French village of Laignes, Christine Petit developed a strong interest in science. “I was always driven by curiosity and a need to understand things,” she recalls. Her father, a physicist, and her mother, who came from a family of winemakers, encouraged that curiosity and supported her decision in 1967 to pursue a medical degree at Pierre and Marie Curie University (Paris VI). Petit soon discovered, however, that clinical medicine was not enough to sate her scientific interests. “I needed to understand deeply what was going on in patients, and I realized that genetics offered a very powerful approach to doing that,” she says. So, while attending medical school, Petit took biochemistry and genetics classes at the University of Paris XI at Orsay, and then in the Institut Pasteur, graduating with a master’s degree in those two subjects in 1973. A year later, she also received her doctorate in medicine.
Soon afterward, Petit entered a doctoral program in natural sciences and biochemistry at the Institut Pasteur, where she trained in the laboratory of biologist (and Nobel laureate) Francois Jacob. For her post-doctoral work, Petit went to the Institute of Immunology in Basel, Switzerland, before taking a research position at the CNRS (French National Center for Scientific Research) in Gif-sur-Yvette. She returned to the Institut Pasteur as a staff scientist in 1985, where she worked with geneticist Jean Weissenbach on sex determination in humans.
In 1993, Petit established her own lab at the Institut Pasteur. By now, the genomic revolution was fully underway, and Petit had turned her focus to the genetic and molecular mechanisms involved in the development and function of human sensory systems. Her fascination with this area of research was driven in part by the sensory experiences of her childhood in rural France, she says, including a deep love of music. (Everyone in her family played at least one musical instrument.) “I strongly believe that we tend to underestimate the role of our sensory environment in the construction of our personality. Much more care should be taken with its quality. This is particularly true for the sound environment,” says Petit.
Petit started by researching the olfactory system. She identified the gene (KAL1) and the protein it encodes (anosmin-1) responsible for Kallmann syndrome, a condition characterized by delayed or absent puberty and an impaired sense of smell. Petit then turned her attention to the auditory system. In the early 1990s, little was known about the molecules involved in hearing loss. The reason: The cochlea (the auditory sensory organ) has only a few thousand sensory (hair) cells, and those cells are arranged in a way that makes them difficult for scientists to access and isolate through biochemical procedures. Petit thought that a genetics approach—searching for genetic defects that cause deafness—offered the best way of understanding the functioning of the auditory system. “It was a very exciting adventure,” she says. “At that time, not a single gene responsible for profound deafness had been mapped to the human chromosome, a mandatory step to identify causal disease genes at the time.”
Petit began her search for those genes by looking at the transmission of given gene defects through large, geographically isolated families in Northern Africa and the Middle East with a history of profound hearing loss. In those remote regions of the world, many marriages are consanguineous (between first or second cousins), a factor that makes it easier to identify the genes involved in recessive genetic disorders. This innovative approach led Petit to map to the human chromosome—for the first time—two genes (DFNB1 and DFNB2) responsible for recessive forms of profound congenital deafness. She and her team then went on to identify more than 20 genes that cause various forms of hearing impairment among the most severe and the most frequent.
“Our objective was to elucidate the molecular mechanisms of hearing using as entry points the genes responsible for human deafness. But a deep understanding could and still today can only be obtained from animal models of these deafness forms. These models allow to set up the multidisciplinary approach that is required for elucidate how the cochlea responds to sound and encodes the mechanical acoustic signals into electrical signals then process all along the central auditory pathway,” says Petit. So Petit and her team developed a variety of mouse models so as to decipher both the early and late roles of these genes and for some of them, their peripheral and central roles. A series of groundbreaking studies followed in which Petit described how various genes and the proteins are involved in the normal neurodevelopmental and neurophysiological processes in the cochlea, especially how the sensory hair cells, respond to mechanical sound vibrations, convert them into electrical signals that will generate nerve impulses that travel to the brain. She also described how hearing goes awry when mutations in these genes interfere with that transmission. One of the early medical conditions that Petit’s lab targeted was Usher syndrome, a recessive genetic disorder that can affect both hearing and vision. Petit demonstrated how the proteins encoded by the genes involved in Usher syndrome impact the early development and then the mechanotransduction machinery of the cochlea’s hair cells. These and other findings from Petit’s lab have had a transformative impact on the diagnosis and treatment of hereditary hearing loss, including the ongoing development of promising gene therapies for both congenital and late-forming types of deafness.
In addition to professorships at the Institut Pasteur and the Collège de France, Petit is founding director of the Hearing Institute, a collaborative research venture of the Institut Pasteur, la Fondation pour l’Audition and INSERM (the French National Institute of Health and Medical Research). Petit has been bestowed with numerous honors and awards during her career, including membership in the French Academy of Sciences, the Academia Europae, and the Norwegian Academy of Sciences and Letters. She is also a foreign associate of the National Academy of Sciences and the National Academy of Medicine.
Petit lives in a Paris suburb with her husband, hepato-gastroenterologist Jacques Petit, MD. They have a daughter, who is a medical doctor, and a son, who is a jazz cellist.