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  • Title: Apolipoprotein C-II deficiency with no rare variant in the APOC2 gene.
    Author: Takase S, Osuga J, Fujita H, Hara K, Sekiya M, Igarashi M, Takanashi M, Takeuchi Y, Izumida Y, Ohta K, Kumagai M, Nishi M, Kubota M, Masuda Y, Taira Y, Okazaki S, Iizuka Y, Yahagi N, Ohashi K, Yoshida H, Yanai H, Tada N, Gotoda T, Ishibashi S, Kadowaki T, Okazaki H.
    Journal: J Atheroscler Thromb; 2013; 20(5):481-93. PubMed ID: 23470567.
    Abstract:
    AIM: Familial apolipoprotein C-II (apoC-II) deficiency is a rare autosomal recessive disorder with marked hypertriglyceridemia resulting from impaired activation of lipoprotein lipase. In most cases of apoC-II deficiency, causative mutations have been found in the protein-coding region of APOC2; however, several atypical cases of apoC-II deficiency were reported to have markedly reduced, but detectable levels of plasma apoC-II protein (hereafter referred to as hypoapoC-II), which resulted from decreased promoter activity or improper splicing of apoC-II mRNA due to homozygous mutations in APOC2. Here we aim to dissect the molecular bases of a new case of hypoapoC-II. METHODS: We performed detailed biochemical/genetic analyses of our new case of hypoapoC-II, manifesting severe hypertriglyceridemia (plasma triglycerides, 3235 mg·dL(-1)) with markedly reduced levels of plasma apoC-II (0.6 mg·dL(-1)). RESULTS: We took advantage of a monocyte/macrophage culture system to prove that transcription of apoC-II mRNA was decreased in the patient's cells, which is compatible with the reported features of hypoapoC-II. Concomitantly, transcriptional activity of the minigene reporter construct of the patient's APOC2 gene was decreased; however, no rare variant was detected in the patient's APOC2 gene. Fifty single nucleotide variants were detected in the patient's APOC2, but all were common variants (allele frequencies ＞35%) that are supposedly not causative. CONCLUSIONS: A case of apoC-II deficiency was found that is phenotypically identical to hypoapoC-II but with no causative mutations in APOC2, implying that other genes regulate apoC-II levels. The clinical entity of hypoapoC-II is discussed.
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