1. A French multigeneration pedigree with hyperlipoproteinaemia was investigated for the transmission of the rare apolipoprotein E1(Gly127 → Asp, Arg158 → Cys) variant. The proband, a 46-year-old male carrying the rare apoE1 variant, presented a severe type III hyperlipoproteinaemia like his three brothers and his sister.
2. ApoE phenotyping and genotyping showed a discrepancy in the second allele carried by the proband's wife and two of her children, thus suggesting another apoE gene mutation. Cloning and sequencing of the entire exon 4 demonstrated a point mutation at codon 251, leading to an apoE3(Cys112 → Arg, Arg251 → Gly) allele. The proband's wife was normolipaemic and heterozygous for this rare isoform and the common apoE3 protein. The rare apoE3(Cys112 → Arg, Arg251 → Gly) allele has been transmitted to her two daughters. The first, aged 19, was normolipaemic and heterozygous for this allele and the common apoE2 allele. The second, carrying both the rare isoforms apoE1(Gly127 → Asp, Arg158 → Cys) and apoE3(Cys112 → Arg, Arg251 → Gly), presented a hypertriglyceridaemia at the age of 10.
3. The exploration of apoE status associated with plasma lipid levels and lipoprotein profiles in this three-generation pedigree made it possible to describe a compound heterozygote for two mutated alleles, one mutation being located in the N-terminal domain of the apoE protein and the other arising in the C-terminal domain.