G.O.21: Relapsing immune mediated polyneuropathy, strokes and chronic haemolysis due to inherited CD59 deficiency

Abstract

Primary CD59 deficiency in humans has been reported only recently. The original patient had cerebral infarction and elements of paroxysmal nocturnal haemoglobinuria. Activation of the membrane attack complex (MAC) is responsible from the clinical events. In another family with this condition the index cases presented with chronic haemolysis and immune mediated neuropathy. Lastly, a 7-month old infant has been noted with bulbar symptoms. In a two generation-three affected large sibship, we have detected early onset immune mediated neuropathy, strokes both in the anterior and posterior circulation, and mild chronic Coombs negative haemolysis. The onset was as early as 8months of age. There was a timely- order in the symptoms developing: strokes first followed by neuropathy and haemolysis detected during follow up. Neuropathy was mainly axonal which was partially responsive to IVIg treatment. When retrospectively evaluated, the second patient had a chronic cerebellar lesion suggested by diffuse cerebellar volume loss and T2 hyperintensity. Additionally, chronic right deep cerebral white matter lesion was seen. The third case in this family had a small encephalocele of the left temporal lobe. Linkage analysis and homozygosity mapping by using SNP microarrays revealed 10 candidate loci covering 0.33% of the genome. Whole exome sequencing in one index case combined with linkage analysis allowed identifying a homozygous missense mutation (NM_000611: exon3: c. A146T: p. D49V) in the CD59 gene. The mutation was validated by Sanger sequencing. Sanger Sequencing of the other family members revealed a cosegregation of the mutation with the disease phenotype and parents were heterozygous for the mutation as expected. This mutation was found in neither EVS, dbSNPv138 nor 95 ethnically matched controls. Our study contributes to the understanding of autoimmune neuropathies characterized by a novel genetic abnormality leading to activation of MAC.