Nationwide screening identifies an expanded clinical spectrum of anti-KLHL11 antibody-associated neurologic disease in Japan.

OBJECTIVE

To define the clinical spectrum and treatment responses of anti-Kelch-like protein 11 (KLHL11) IgG-associated neurological syndromes by screening a large, expanded cohort of patients with suspected autoimmune cerebellar ataxia (ACA), autoimmune encephalitis (AE), and related neurological disorders.

METHODS

In this retrospective, observational study, serum samples from 930 patients collected from over 100 medical institutions across Japan between 2002 and 2025 were screened. The study population was categorized into five cohorts: cerebellar ataxia (CA) of unknown etiology (n = 778), AE (n = 49), brainstem encephalitis (n = 2), myelitis (n = 12), and multiple system atrophy (MSA) (n = 89). Anti-KLHL11 antibodies were detected using a fixed cell-based assay with HEK293T cells. Cerebrospinal fluid was analyzed in all serum-positive cases.

RESULTS

Anti-KLHL11 antibodies were identified in four cases, three males and one female with a mean onset age > 60 years, all showing dual positivity in serum and cerebrospinal fluid. The clinical phenotypes consisted of predominantly CA (n = 2), combined limbic encephalitis (LE) and CA (n = 1), and isolated LE associated with small-cell lung cancer (n = 1). Notably, none of the cases were associated with testicular tumor. While typical paraneoplastic presentations were observed, one patient had no detectable malignancy and improved with immunotherapy alone, and another showed neurological recovery following treatment of a non-testicular tumor. Anti-KLHL11 antibodies were absent in all disease controls with MSA.

CONCLUSIONS

Expanding our initial findings, this nationwide study indicates that anti-KLHL11 antibody-associated ACA and AE are rare but increasingly recognized in Japan and may be under-recognized globally. The clinical spectrum of anti-KLHL11 antibody-associated neurological diseases is broad, including females and individuals without a detectable testicular tumor. Importantly, patients presenting with AE may show more favorable responses to immunotherapy or tumor-directed treatment than those with isolated CA, highlighting the importance of early recognition and phenotype-specific management.