Original Article

Vitamin A is linked to the expression of the AI-CIII-AIV gene cluster in familial combined hyperlipidemia

Correspondence to: Josep Ribalta

There is growing evidence of the capacity of vitamin A to regulate the expression of the genetic region that encodes apolipoproteins (apo) A-I, C-III, and A-IV. This region in turn has been proposed to modulate the expression of hyperlipidemia in the commonest genetic form of dyslipidemia, familial combined hyperlipidemia (FCHL). The hypothesis tested here was whether vitamin A (retinol), by controlling the expression of the AI-CIII-AIV gene cluster, plays a role in modulating the hyperlipidemic phenotype in FCHL. We approached the subject by studying three genetic variants of this region: a C₁₁₀₀–T transition in exon 3 of the apoC-III gene, a G₃₂₀₆–T transversion in exon 4 of the apoC-III gene, and a G_-75–A substitution in the promoter region of the apoA-I gene. The association between plasma vitamin A concentrations and differences in the plasma concentrations of apolipoproteins A-I and C-III based on the different genotypes was assessed in 48 FCHL patients and 74 of their normolipidemic relatives. The results indicated that the subjects carrying genetic variants associated with increased concentrations of apoA-I and C-III (C₁₁₀₀–T and G_-75–A) also presented increased plasma concentrations of vitamin A. This was only observed among the FCHL patients, which suggested that certain characteristics of these patients contributed to this association. The G₃₂₀₆–T was not associated with changes in either apolipoprotein concentrations or in vitamin A.

In summary, we report a relationship between genetically determined elevations of proteins of the AI-CIII-AIV gene cluster and vitamin A in FCHL patients. More studies will be needed to confirm that vitamin A plays a role in FCHL which might also be important for its potential application to therapeutical approaches.—Ribalta, J., J. Girona, J. C. Vallvé, A. E. La Ville, M. Heras, and L. Masana. Vitamin A is linked to the expression of the AI-CIII-AIV gene cluster in familial combined hyperlipidemia. J. Lipid Res. 1999. 40: 426– 431.

Supplementary key words: peroxisome proliferator activated receptor, retinoid X receptor, retinoic acid, hyperapoB, fibrates, syndrome X

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