Complement Dysregulation in Infancy: A Case of CD59 Deficiency With Neurological Sequelae

CD59 deficiency is a rare autosomal recessive disorder causing complement-mediated hemolysis, strokes, and neuropathy. Early recognition is critical to avoid irreversible complications. We report a two-year-old girl, born to consanguineous parents, who presented with recurrent hypotonia, motor regression, ischemic stroke, and Coombs-negative hemolytic anemia. Whole exome sequencing confirmed a homozygous CD59 mutation (c.323C>A; p.Ser108). She was treated with immune-moderating therapy and anticoagulants with a rehabilitation program. Despite therapy, she developed persistent neurological deficits and failure to thrive. CD59 deficiency should be considered in infants with unexplained hypotonia, stroke, and hemolytic anemia. Early diagnosis and complement inhibition may reduce complications.