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Functional and molecular studies in primary carnitine deficiency.

Authors
  • Frigeni, Marta1
  • Balakrishnan, Bijina1
  • Yin, Xue1
  • Calderon, Fernanda R O2, 3
  • Mao, Rong2, 3
  • Pasquali, Marzia1, 2, 3
  • Longo, Nicola1, 2, 3
  • 1 Division of Medical Genetics/Pediatrics, University of Utah, Salt Lake City, Utah.
  • 2 ARUP Institute for Clinical and Experimental Pathology®, ARUP Laboratories, Salt Lake City, Utah.
  • 3 Department of Pathology, University of Utah, Salt Lake City, Utah.
Type
Published Article
Journal
Human Mutation
Publisher
Wiley (John Wiley & Sons)
Publication Date
Dec 01, 2017
Volume
38
Issue
12
Pages
1684–1699
Identifiers
DOI: 10.1002/humu.23315
PMID: 28841266
Source
Medline
Keywords
License
Unknown

Abstract

Primary carnitine deficiency is caused by a defect in the OCTN2 carnitine transporter encoded by the SLC22A5 gene. It can cause hypoketotic hypoglycemia or cardiomyopathy in children, and sudden death in children and adults. Fibroblasts from affected patients have reduced carnitine transport. We evaluated carnitine transport in fibroblasts from 358 subjects referred for possible carnitine deficiency. Carnitine transport was reduced to 20% or less of normal in fibroblasts of 140 out of 358 subjects. Sequencing of the 10 exons and flanking regions of the SLC22A5 gene in 95 out of 140 subjects identified causative variants in 84% of the alleles. The missense variants identified in our patients and others previously reported (n = 92) were expressed in CHO cells. Carnitine transport was impaired by 73 out of 92 variants expressed. Prediction algorithms (Polyphen-2, SIFT) correctly predicted the functional effects of expressed variants in about 80% of cases. These results indicate that mutations in the coding region of the SLC22A5 gene cannot be identified in about 16% of the alleles causing primary carnitine deficiency. Prediction algorithms failed to determine the functional effects of amino acid substitutions in this transmembrane protein in about 20% of cases. Therefore, functional studies in fibroblasts remain the best strategy to confirm or exclude a diagnosis of primary carnitine deficiency.

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