Impaired IgG responses in a child with homozygous C2 deficiency and recurrent pneumococcal septicaemia.

Homozygous deficiency of the second component of complement (C2) is the most common inherited deficiency of complement. Although C2 deficiency has been detected in asymptomatic individuals, patients usually present with either autoimmune disease or recurrent pyogenic infection, particularly due to encapsulated bacteria such as Streptococcus pneumoniae, Haemophilus influenzae type b and Neisseria meningitidis. Interestingly, infection is the most common mode of presentation of C2 deficiency in young children (1). An association between C2 deficiency and IgG subclass deficiency has also been previously described. We now report a female child with C2 deficiency that presented at the age of 3 mo with recurrent pneumococcal septicaemia. Although IgG subclass levels were normal, specific IgG responses to vaccination against S. pneumoniae and H. influenzae were significantly impaired.