Complement Dysregulation Syndromes in Children and Adolescents

The perceived complexity of the complement system has limited the understanding of its prevalence within many disease processes. Well-known disorders such as Shiga Toxin E. coli hemolytic uremic syndrome (STEC HUS) have overshadowed emerging lesser-known diseases such as atypical hemolytic uremic syndrome (aHUS), Streptococcus pneumoniae hemolytic uremic syndrome (spHUS), paroxysmal nocturnal hemoglobinuria (PNH), and congenital CD59 deficiency in the pediatric population. Unfortunately, delays in differential consideration and diagnosis of such complement dysregulation syndromes in children often lead to catastrophic outcomes. Morbidity and mortality have been reduced through early recognition and implementation of appropriate therapeutic interventions. This chapter will portray a more abridged version of the physiologic mechanisms of complement and its relation to pediatric disease processes with the goal of improving awareness through a broader understanding.