CD99L2 Identified as Novel Disease Gene for Spastic Ataxia and Hereditary Spastic Paraplegia
Key Insights
Researchers at Ruhr University Bochum (search) and Tübingen have identified CD99L2 (search), a gene previously known only for immune function, as a novel cause of rare movement disorders including spastic ataxia (search) and hereditary spastic paraplegia (search).
The study, published in Nature Communications, demonstrates that CD99L2 (search) protein acts as an activating partner for CAPN1 (search), a calcium-dependent protease already implicated in these neurodegenerative conditions.
Disease-causing variants disrupt CD99L2 (search) protein production and prevent its interaction with CAPN1 (search), leading to impaired neuronal signaling and synaptic dysfunction in affected patients.
A research team led by scientists at Ruhr University Bochum (search) and the University of Tübingen has uncovered a previously unknown genetic cause of rare movement disorders, revealing that the gene CD99L2 (search)—long recognized solely for its role in the immune system—is essential for normal neuronal communication and, when mutated, drives spastic ataxia (search) and hereditary spastic paraplegia (search).
The findings, published in Nature Communications, resolve a long-standing diagnostic gap for patients with unexplained movement disorders and offer fresh insight into the molecular underpinnings of neurodegeneration.
A Gene with a Hidden Neurological Role
Before this study, CD99L2 (search) had no established neurological function. It was primarily known for its involvement in immune system processes. Using a combination of genome-wide genetic analysis and laboratory experiments in cells, the research team demonstrated that CD99L2 is also critical for communication pathways within nerve cells.
The large-scale genetic analysis of the patient cohort was carried out in Tübingen under the supervision of Dr. Tobias Haack. Functional studies of the newly identified disease gene were led by Dr. Jonasz Weber and colleagues at the Department of Human Genetics at Ruhr University Bochum (search).
How CD99L2 (search) Disruption Affects Neuronal Signaling
The researchers found that the protein produced by CD99L2 (search) functions as an activating partner for CAPN1 (search), a calcium-dependent protease already known to be involved in hereditary spastic paraplegia (search) and ataxia. When CD99L2 is mutated, this critical interaction is lost.
“Disease-causing variants lead to disrupted production of the CD99L2 (search) protein in the cell and prevent its interaction with CAPN1 (search),” explained Dr. Jonasz Weber. “Patients' cells also showed specific disruptions of synaptic processes.”
Defects in CD99L2 (search) reduce the activation of CAPN1 (search), which in turn disrupts important neuronal signaling pathways. This cascade of molecular events provides a likely explanation for the movement-related symptoms—including difficulty walking, poor balance, and muscle stiffness—seen in affected patients.
Bridging Genetics and Functional Neuroscience
The study underscores the value of integrating genetic diagnostics with functional studies of how genes operate inside cells. Rather than treating these as separate domains, the researchers argue that only their close collaboration can yield reliable disease mechanisms from genetic variants.
“Our results show that genetic diagnostics and functional neuroscience are not mutually exclusive areas,” said Weber. “Only when both disciplines work closely together can a reliable disease mechanism be derived from a genetic variant.”
Clinical Implications for Rare Movement Disorders
Spastic ataxia (search) encompasses a group of rare neurodegenerative disorders characterized by problems with movement coordination (ataxia) together with spastic paralysis. Symptoms result from damage affecting the cerebellum and motor pathways within the central nervous system. The age at which symptoms appear and disease progression can vary widely depending on the underlying genetic cause.
Identifying CD99L2 (search) as a disease-causing gene could improve genetic diagnosis for people with rare movement disorders who have gone years without clear answers. It also provides researchers with new information about the biological processes involved in neurodegeneration.
Although no cure currently exists for these disorders, understanding how CD99L2 (search) affects nerve communication may eventually guide the development of new therapies that target the root cause of the disease rather than merely addressing symptoms. Scientists note that further research is needed to determine how common these gene changes are and whether CD99L2 variants contribute to other neurological conditions.