Background. CD59 is the principal cell inhibitor of complement membrane attack on cells. Stroke, peripheral neuropathy, and recurrent central nervous system attacks have been reported in patients with inherited CD59 deficiency. In this paper, we report a patient with CD59 deficiency associated with two attacks of demyelinating peripheral neuropathy and the third attack as an isolated optic neuritis.

Case. An 8-month-old girl whose sibling died at 12th month of age with recurrent weakness episodes responsive to intravenous immune globulin treatment, presented with weakness in legs and poor sucking. Weakness episodes with neurogenic electromyography suggested CD59 deficiency. Immunophenotypic analysis with flow cytometry showed CD59 deficiency. Sanger sequencing of CD59 gene revealed a homozygous c146delA (p.Asp49Valfs*32) mutation. First two attacks were treated with intravenous immunoglobulin therapy without any sequalae. Third attack was an isolated optic neuritis which could not be explained by any other entity. The patient had no response to intravenous immunoglobulin but benefited from pulse steroid therapy. Eculizumab was started every two weeks in order to prevent possible advanced attacks and to reduce their severity.

Conclusion. Although it is a rarely reported disease, better recognition of CD59 deficiency by pediatric neurologists is necessary because it is curable. In addition to different presentations reported, optic neuritis may also be a manifestation of CD59 deficiency.

Keywords: complement inhibition, demyelinating, eculizumab, immune dysregulation, optic neuritis