Amat di San Filippo Cristina, Taylor Matthew R G, Mestroni Luisa, Botto Lorenzo D, Longo Nicola
Division of Medical Genetics, Departments of Pediatrics and Pathology, University of Utah, 2C412 SOM, 50 North Medical Drive, Salt Lake City, UT 84132, USA.
Mol Genet Metab. 2008 Jun;94(2):162-6. doi: 10.1016/j.ymgme.2008.02.002. Epub 2008 Mar 11.
Carnitine is essential for the transfer of long-chain fatty acids across the mitochondrial membrane for subsequent beta-oxidation. A defect in the high-affinity carnitine transporter OCTN2 causes autosomal recessive primary carnitine deficiency that can present with hypoketotic hypoglycemia, mainly in infancy or cardiomyopathy. Heterozygotes for primary carnitine deficiency can have mildly reduced plasma carnitine levels and can develop benign cardiac hypertrophy. In animal models, heterozygotes for this disease have a higher incidence of cardiomyopathy with aging. This study tested whether heterozygosity for primary carnitine deficiency was associated with cardiomyopathy. The frequency of mutations in the SLC22A5 gene encoding the OCTN2 carnitine transporter was determined in 324 patients with cardiomyopathy and compared to that described in the normal population. Missense variations identified in normal controls and patients with cardiomyopathy were expressed in Chinese Hamster Ovary cells to confirm a functional effect. Exons 2-10 of the SLC22A5 gene were amplified by PCR in the presence of LCGreen I and analyzed by dye-binding/high-resolution thermal denaturation. Exon 1 of the gene was sequenced in all patients. Heterozygosity for a few variants (L144F, T264M, I312V, E317K, and R488H) was found in 6/324 patients with cardiomyopathy. Expression of these variants in CHO cells indicated that T264M decreased, E317K increased, while L144F, I312V, and R488H did not significantly affect carnitine transport. Expression in CHO cells of all the variants identified in a normal population indicated that only two had a functional effect (L17F and Y449D), while L144F, V481I, V481F, M530V, and P549S did not change significantly carnitine transport. The frequency of variants affecting carnitine transport was 2/324 patients with cardiomyopathy (0.61%) not significantly different from frequency of 3/270 (1.11%) in the general population. These results indicate that heterozygosity for primary carnitine deficiency is not more frequent in patients with unselected types of cardiomyopathy and is unlikely to be an important cause of cardiomyopathy in humans.
肉碱对于长链脂肪酸穿过线粒体膜以进行后续的β氧化过程至关重要。高亲和力肉碱转运体OCTN2的缺陷会导致常染色体隐性遗传的原发性肉碱缺乏症，主要在婴儿期可表现为低酮性低血糖症或心肌病。原发性肉碱缺乏症的杂合子血浆肉碱水平可能会轻度降低，并可能发展为良性心脏肥大。在动物模型中，随着年龄增长，这种疾病的杂合子患心肌病的发生率更高。本研究检测原发性肉碱缺乏症的杂合性是否与心肌病相关。在324例心肌病患者中确定了编码OCTN2肉碱转运体的SLC22A5基因的突变频率，并与正常人群中描述的频率进行比较。在正常对照和心肌病患者中鉴定出的错义变异在中国仓鼠卵巢细胞中表达以确认其功能效应。在存在LCGreen I的情况下通过PCR扩增SLC22A5基因的外显子2 - 10，并通过染料结合/高分辨率热变性进行分析。对所有患者的该基因外显子1进行测序。在324例心肌病患者中有6例发现了一些变异（L144F、T264M、I312V、E317K和R488H）的杂合性。这些变异在CHO细胞中的表达表明，T264M使转运减少，E317K使转运增加，而L144F、I312V和R488H对肉碱转运没有显著影响。在正常人群中鉴定出的所有变异在CHO细胞中的表达表明，只有两个变异（L17F和Y449D）具有功能效应，而L144F、V481I、V481F、M530V和P549S对肉碱转运没有显著改变。影响肉碱转运的变异频率在324例心肌病患者中为2/324（0.61%），与普通人群中3/270（1.11%）的频率无显著差异。这些结果表明，原发性肉碱缺乏症的杂合性在未选择的心肌病类型患者中并不更常见，不太可能是人类心肌病的重要病因。
