| Summary: | Inherited complement deficiencies are rare, particularly those associated with late components of the complement cascade. We report a 5-year-4-month-old Taiwanese boy with systemic meningococcal infection who had undetectable CH50 level of < 6 U/mL (normal, 32.6-39.8 U/mL). Levels of C3, C4, C5, C6 and C8 were normal, but C7 was undetectable (<5.8 mg/dL; reference, 55-85 mg/dL). The patient's sister was also C7-deficient (CH50 < 6 U/mL, C7 < 5.8 mg/dL). His father's CH50 was 25.9 U/mL and C7 was 27.8 mg/dL. His mother's CH50 was 31.2 U/mL and C7 was 22.7 mg/dL. His parents thus both had a partial complement deficiency, indicating an autosomal codominant inheritance pattern. Awareness of the possibility of late complement deficiency is important as they comprise a small percentage of patients who present with disseminated meningococcal disease or other serious infections caused by encapsulated organisms.
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