Abstract
CD59 deficiency is a common finding in RBCs and WBCs in patients with chronic hemolysis suffering from paroxysmal nocturnal hemoglobinuria in which the acquired mutation in the PIGA gene leads to membrane loss of glycosylphosphatidylinositol-anchored membrane proteins, including CD59. The objective of the present study was to elucidate the molecular basis of childhood familial chronic Coombs-negative hemolysis and relapsing polyneuropathy presenting as chronic inflammatory demyelinating polyradiculoneuropathy in infants of North-African Jewish origin from 4 unrelated families. A founder mutation was searched for using homozygosity mapping followed by exome sequencing. The expression of CD59, CD55, and CD14 was examined in blood cells by flow cytometry followed by Western blot of the CD59 protein. A homozygous missense mutation, p.Cys89Tyr in CD59, was identified in all patients. The mutation segregated with the disease in the families and had a carrier rate of 1:66 among Jewish subjects of North-African origin. The mutated protein was present in the patients' cells in reduced amounts and was undetectable on the membrane surface. Based on the results of the present study, we conclude that the Cys89Tyr mutation in CD59 is associated with a failure of proper localization of the CD59 protein in the cell surface. This mutation is manifested clinically in infancy by chronic hemolysis and relapsing peripheral demyelinating disease.