Scientists Uncover Genetic Link Behind Rare X-Linked Spastic Ataxia

A groundbreaking study has uncovered a key genetic cause of X-linked spastic ataxia, a rare neurodegenerative disorder. Researchers identified mutations in the CD99L2 gene that disrupt its role in activating CAPN1, a critical enzyme for neuronal health. The findings, published in Nature Communications in 2026, reveal a previously unknown molecular pathway linked to the disease.

The research, led by Menden, Incebacak Eltemur, and colleagues, examined 12 families affected by X-linked spastic ataxia. Participants came from Germany, Turkey, the USA, and Australia, all sharing a pattern of progressive motor decline. The team discovered that loss-of-function variants in CD99L2 prevent proper activation of CAPN1, a calcium-dependent protease essential for synaptic remodelling and neuronal plasticity.

Without functional CD99L2, CAPN1 fails to activate, leading to cellular dysfunction and neuronal death. Hemizygous males with these mutations develop severe, early-onset spastic ataxia, marked by muscle stiffness and coordination loss. Heterozygous females, however, often show milder symptoms or remain asymptomatic.

The study not only pinpoints CD99L2 as a critical regulator of CAPN1 but also highlights its broader relevance in neurodegenerative disease. Disruptions in protease regulation, as seen here, may contribute to wider neuronal degeneration beyond spastic ataxia.

These findings open doors for new treatments, including gene editing and small-molecule drugs targeting the CD99L2-CAPN1 pathway. By clarifying the molecular roots of spastic ataxia, the research provides a foundation for developing precision therapies. Further studies may extend these insights to other neurodegenerative conditions linked to protease dysfunction.