C1q deficiency in an Inuit family: Identification of a new class of C1q disease-causing mutations

C1q deficiency is a rare condition associated with a systemic lupus erythematosus (SLE)-like syndrome and recurrent infections. e present the molecular basis behind C1q deficiency in three sisters of Inuit origin. Initial examination for complement deficiency showed no function of the classical complement activation pathway in the patients; the lectin and alternative pathways were intact. No C1q or low molecular weight C1q was detected in sera and no anti-C1q autoantibodies were found. cing of the C1q genes revealed a novel missense mutation (Gly-Arg) in codon 217 of the B chain. All sisters were homozygous for the mutation: both parents were heterozygous. None of 100 healthy controls carried the mutation. ndings define a third class of molecular mechanisms behind C1q deficiency, where missense mutations cause a lack of detectable C1q-antigen in serum.