Growth‐associated protein 43 in lesions and cerebrospinal fluid in multiple sclerosis

Axonal damage in multiple sclerosis (MS) is correlated to disease progression. Early axonal damage may be compensated for by regenerative processes. Growth‐associated protein 43 (GAP‐43) is a marker for axonal growth and synaptogenesis in various neurodegenerative diseases. We investigated the expression of GAP‐43 in 48 MS grey and white matter lesions of different stages. Decreased GAP‐43 expression was found in 74% of the white matter lesions, independent of the lesion stage. In 19 out of 35 white matter lesions, areas of increased GAP‐43 expression were present immediately adjacent to the lesions. Increased or unaltered expression was observed in remyelinated lesions. GAP‐43 was expressed in neurofilament‐positive structures. GAP‐43 expression appeared unchanged in grey matter lesions. Macrophages were present in the areas of changed GAP‐43 expression. cerebrospinal fluid GAP‐43 levels were negatively correlated with magnetic resonance imaging measures of whole‐brain atrophy (r = −0.30). In conclusion, these results indicate that decreased GAP‐43 immunopositivity reflects axonal damage in MS lesions, which may again be reflected in decreased cerebrospinal fluid levels. The increased levels of GAP‐43 in remyelinated or nondemyelinated white matter close to MS lesions may reflect regenerative attempts by damaged axons.