Researchers document first known cases of Marfan syndrome in domestic cats

As kittens, brothers Gary and Shaggy had noticeably longer limbs, and later examinations revealed problems with the structures of their eyes and enlargement of the aorta.¹ Workup confirmed bilateral lens luxation and aortic root dilation, which the study authors identified as the cardinal features of Marfan syndrome (MFS), as well as long limbs.²

Histopathologic examination of the ascending aorta showed disrupted and fractured elastic fiber tendrils, consistent with impaired fibrillin-1 function.²

Their cases, described in a study published in Scientific Reports, are the first molecular characterization of MFS in domestic cats. Researchers at Cornell University College of Veterinary Medicine and its Baker Institute for Animal Health, working with outside collaborators, found that both random-bred littermates carried a variant in the fibrillin 1 (FBN1) gene.^1,2

MFS is a rare inherited connective tissue disorder that affects about 1 in 4,000 humans.¹ The disease is autosomal dominant and caused by FBN1 variants, and spontaneous animal models are rarely reported, according to the study authors.² FBN1 codes for fibrillin-1, a protein found in blood vessels, bones, ligaments, skin, and eyes.¹

Two copies, partial function

Whole genome sequencing found a homozygous splice region variant located 3 base pairs upstream of FBN1 exon 22. The variant was absent in a comparison cohort of more than 1,000 cats.² Each cat inherited 2 altered copies of the gene, 1 from each parent.¹

That inheritance pattern stands out because a single altered copy is enough to cause MFS in humans.¹ The team used Oxford Nanopore sequencing of complementary DNA to see how the variant affects splicing. Exon 22 was skipped in 73% of transcripts, which disrupts the second hybrid domain of fibrillin-1.²

The variant is hypomorphic, meaning it reduces gene function without eliminating it. Because the splice site is "leaky," it still produces low levels of normal transcript. The authors described this as functional heterozygosity: the cats are genetically homozygous, but at the molecular level they behave more like heterozygotes.² According to Cornell, this partial function likely explains why the cats survived into adulthood.¹

Implications for diagnostics and research

"The findings provide a foundation for improved veterinary diagnostics," said Jacquelyn Evans, PhD, assistant professor at the Baker Institute for Animal Health, and senior author.¹ "It can help veterinarians recognize similar cases in the future and may help develop genetic tests."

The authors said the cases provide comparative insight into the genetic and molecular basis of MFS.²

Evans also pointed to the role of clients in the discovery. "This discovery is a great example of how [clients] can collaborate with veterinary and genetic experts to learn something that could help other animals in the future," she said. "It also showcases the comparative approach that has long been central to research at the Baker Institute for Animal Health."¹

Collaborators included researchers from Ghent University in Belgium, the University of Pennsylvania, and the Schwarzman Animal Medical Center in New York City.¹

References

1. Griffin T. First known case of Marfan syndrome discovered in feline siblings. Cornell Chronicle. September 24, 2026. Accessed September 28, 2026. https://news.cornell.edu/stories/2026/09/first-known-case-marfan-syndrome-discovered-feline-siblings
2. Cook SR, Hayward JJ, Cheong SH, et al. A homozygous hypomorphic FBN1 splice region variant in domestic cats with Marfan syndrome. Sci Rep. Published online September 19, 2026. doi:10.1038/s41598-026-70702-3