A homozygous point mutation results in a stop codon in the C1q B-chain of a C1q-deficient individual.
Southern blot analysis of the B-chain genes in one of eight C1q-deficient individuals revealed an abnormal banding pattern. The defect, which was homozygous, could be localized by restriction mapping to a single Taq I site within residue 150 in the coding region of the B-chain gene. DNA sequencing across the site revealed a stop codon that would cause premature termination of the protein product. No material corresponding to the A or C chains, or a truncated B chain, could be identified by antigenic analysis of the patient's serum, indicating that a complete B chain is required for secretion of a C1q molecule.
D003062:Codon; D003166:Complement Activating Enzymes / Q000172:deficiency / Q000235:genetics*; D003172:Complement C1 / Q000172:deficiency / Q000235:genetics*; D015922:Complement C1q; D005260:Female; D006801:Humans; D007153:Immunologic Deficiency Syndromes / Q000235:genetics*; D008297:Male; D012150:Polymorphism, Restriction Fragment Length; D013728:Terminator Regions, Genetic
D003062:Codon; D003172:Complement C1; D015922:Complement C1q; D003166:Complement Activating Enzymes