Compound heterozygosity for an apolipoprotein A1 gene promoter mutation and a structural nonsense mutation with apolipoprotein A1 deficiency.
Apolipoprotein (apo) A1 plays a central role in the metabolism of HDL. We describe a novel genetic variant of the apoA1 gene identified in a patient with low concentrations of plasma HDL cholesterol. The proband, a 12-year-old Japanese boy, exhibited markedly low levels of both plasma apoA1 and HDL cholesterol. Genomic DNA sequencing of apoA1 genes of the patient showed a compound heterozygosity for an A to C substitution at 27 bp upstream of the transcription start site of 1 apoA1 allele, and a C to T substitution in another allele at residue 84 resulting in aberrant termination. The point mutation at nucleotide position -27 changed ATAAATA of the putative TATA box signal sequence to ATACATA. In addition to this mutation, the patient was heterozygous for a G to A substitution at position -75. Immunoblotting of an isoelectric focusing electrophoresis gel of the proband's plasma showed a trace amount of normal apoA1. No measurable plasma apoA1 and HDL cholesterol in a patient with homozygosity for nonsense mutation at residue 84 has been reported previously. To determine the effects of substitution either at position -27 or -75, plasmids containing the 5'-flanking region of the human apoA1 promoter fused to the CAT reporter gene were constructed and transfected in HepG2 cells. A construct with the A to C substitution at position -27 showed 41. 8+/-4.2%, and G to A substitution at position -75 showed 72.8+/-15. 2% (means+/-SD, n=3) of CAT activities, compared with the wild-type promoter sequence. A construct with the double substitutions at positions -27 and -75 showed only 22.8+/-1.3% (mean+/-SD, n=3) activity relative to the wild type. Our patient is the first case with a TATA box mutation etiologically related to lipoprotein disorders.
Matsunaga
A
A
Department of Internal Medicine, Fukuoka University, School of Medicine, Japan.
Sasaki
J
J
Han
H
H
Huang
W
W
Kugi
M
M
Koga
T
T
Ichiki
S
S
Shinkawa
T
T
Arakawa
K
K
D016632:Apolipoprotein A-I / Q000172:deficiency* / Q000235:genetics*; D001053:Apolipoproteins / Q000097:blood; D001483:Base Sequence / Q000235:genetics; D002648:Child; D004247:DNA / Q000032:analysis; D006579:Heterozygote; D006801:Humans; D008055:Lipids / Q000097:blood; D008297:Male; D009154:Mutation / Q000235:genetics*; D010375:Pedigree; D018807:Polymorphism, Single-Stranded Conformational; D011401:Promoter Regions, Genetic / Q000235:genetics*; D016385:TATA Box / Q000235:genetics; D014158:Transcription, Genetic / Q000235:genetics