In an attempt to map the gene (or genes) controlling the synthesis fo the fourth component of complement (C4), we performed linkage studies in a family with hereditary C4 deficiency. The proband, a seven-year-old boy with lupus erythematosus, consistently lacked deteftable serum C4 by both functional and protein measurements. The complement defect was transmitted as an autosomal recessive disorder. Eight of 15 family members were considered to be heterozygotes, seven because of low C4 levels and one because of genetic data (obligate heterozygote). The gene (or genes) coding for C4 deficiency appeared to be linked to the major histocompatibility complex (A2,B12,DW2 on the maternal side and A2,BW15,LD108 on the paternal side) and to other markers known to be in close proximity to the histocompatibility complex on chromosome 6 (phosphoglucomutase-3, glyoxalase-1 and properdin factor B).
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