KEY TAKEAWAYS
- Employing a classical genetic approach to understanding mouse lemurs, Mark Krasnow and his colleagues mapped an inherited heart rhythm disorder without relying on preconceived candidate genes.
- The work identified the unexpected importance of a magnesium transporter — SLC41A2 — in regulating the heart’s pacemaker, expanding our understanding of how cardiac rhythm is controlled.
- Mouse lemurs proved to be a powerful system for studying human diseases and biological mechanisms that directly relate to human health.
Pinpointing which specific genes, molecules, and channels drive disease is an exacting task. For HHMI Investigator Mark Krasnow, identifying the gene behind sick sinus syndrome required patience, curiosity, strategy, and help from a very cute friend — the mouse lemur.
Finding New Ways to Unlock Inherited Illnesses
Sick sinus syndrome is a serious cardiac arrhythmia in which the heart’s natural pacemaker — the sinus node — malfunctions, causing a slow or irregular heartbeat. Though often associated with heart disease and aging, the condition can also be inherited.
As a physician-scientist, Krasnow has devoted his career to understanding human illness through basic science. For decades, he studied genetic diseases in fruit flies and mice, whose short reproductive cycles make inheritance easy to track. But many illnesses common to primates — ranging from lung and metabolic disorders to cardiac arrhythmias — don’t occur in those animals.
Meet the World’s Smallest Primate
Genetically, mouse lemurs are about halfway between mice and humans. They are indigenous only to Madagascar, though they are highly adaptable and can thrive in different environments. And with 24 different recognized mouse lemur species, they possess a wide range of biological differences — just like humans.
Mouse lemurs had already been studied extensively in labs and in the wild. Krasnow and his Stanford University labexternal link, opens in a new tab partnered with ecologists, primatologists, and biologists, visiting well-established labs in France and conducting fieldwork in Madagascar to understand the characteristics and habits of their new research ally.
Students conduct community science to protect Madagascar’s mouse lemurs
Madagascar’s biodiversity offers extraordinary opportunities not only for science, but for education. For the past decade, Krasnow and his team have invited local high school students and teachers to the field station to help map mouse lemur genes and ecosystems — fostering both scientific understanding and appreciation for Madagascar’s unique role as a hotspot for biodiversity.
Locating the Right Cardiac Gene
Although best known for his work on lung disease, Krasnow saw no reason to limit his scope. His team launched systematic genetic screenings of mouse lemurs, developing 70 assays covering anatomy, sensory function, strength, blood chemistry, and cardiac health. Wild lemurs were examined, tagged, and released within hours so researchers could track their health over time.
Among the first 350 mouse lemurs examined in Madagascar, 22 showed human-like cardiac arrhythmias; seven had sick sinus syndrome. All seven were related, and the disease followed an autosomal recessive inheritance pattern. Genome sequencing narrowed the cause to a ten-gene interval.
In humans, sick sinus syndrome had been linked mainly to calcium and sodium ion channels, but those mutations don’t explain all inherited cases. Krasnow’s team expected to find similar genes in mouse lemurs. Instead, they identified a surprising candidate: SLC41A2, a magnesium transporter.
The Overlooked Role of Magnesium
Although previously studied, SLC41A2 had not yet been linked to any specific disease or physiological function. Working with a Stanford cardiology lab, the researchers engineered human stem cells into cardiac pacemaker cells and introduced the SLC41A2 mutation they had identified in the mouse lemurs. The result was a 20 percent reduction in firing rate — exactly what sick sinus syndrome patients experience.
The finding revealed not only the importance of SLC41A2, but also a previously unrecognized role for magnesium in human cardiac health. While cardiologists knew that calcium spikes regulate heart rhythm, Krasnow’s team uncovered magnesium spikes that are equally essential — a finding that thrust a spotlight on these formerly anonymous transporters. Magnesium has long been used clinically to stabilize arrhythmias; identifying the responsible gene now opens new therapeutic possibilities to improve heart health.
Following the Genetic Map Wherever It Leads
With mouse lemurs established as a powerful model for primate-specific diseases, the potential applications are vast — from cardiac and neurodegenerative disorders to metabolic disease and lung conditions.
“We’re still conducting screens and mapping mouse lemur families,” Krasnow says. “We’ll repeat this approach to find other overlooked but clinically important genes. Once we identify the right mutations and mechanisms, we can improve care for both mouse lemurs and humans.”