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Gallant NM, Leydiker K, Wilnai Y, Lee C, Lorey F, Feuchtbaum L, Tang H, Carter J, Enns GM, Packman S, Lin HJ, Wilcox WR, Cederbaum SD, Abdenur JE. Biochemical characteristics of newborns with carnitine transporter defect identified by newborn screening in California. Mol Genet Metab 2017; 122:76-84. [PMID: 28711408 DOI: 10.1016/j.ymgme.2017.06.015] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/07/2017] [Revised: 06/29/2017] [Accepted: 06/30/2017] [Indexed: 12/30/2022]
Abstract
Carnitine transporter defect (CTD; also known as systemic primary carnitine deficiency; MIM 212140) is due to mutations in the SLC22A5 gene and leads to extremely low carnitine levels in blood and tissues. Affected individuals may develop early onset cardiomyopathy, weakness, or encephalopathy, which may be serious or even fatal. The disorder can be suggested by newborn screening. However, markedly low newborn carnitine levels can also be caused by conditions unrelated to CTD, such as the low carnitine levels often associated with normal pregnancies and some metabolic disorders occurring in the mother. In order to clarify the biochemical characteristics most useful for identification of CTD in newborns, we examined California Department of Public Health newborn screening data for CTD from 2005 to 12 and performed detailed chart reviews at six metabolic centers in California. The reviews covered 14 cases of newborn CTD, 14 cases of maternal disorders (CTD, 6 cases; glutaric aciduria, type 1, 5; medium-chain acyl CoA dehydrogenase deficiency, 2; and cobalamin C deficiency, 1), and 154 false-positive cases identified by newborn screening. Our results show that newborns with CTD identified by NBS exhibit different biochemical characteristics, compared to individuals ascertained clinically. Newborns with CTD may have NBS dried blood spot free carnitine near the lower cutoff and confirmatory plasma total and free carnitine levels near the normal lower limit, particularly if obtained within two weeks after birth. These findings raise the concern that true cases of CTD may exist that could have been missed by newborn screening. CTD should be considered as a possible diagnosis in cases with suggestive clinical features, even if CTD was thought to be excluded in the newborn period. Maternal plasma total carnitine and newborn urine total carnitine values are the most important predictors of true CTD in newborns. However, biochemical testing alone does not yield a discriminant rule to distinguish true CTD from low carnitine in newborns due to other causes. Because of this biochemical variability and overlap, molecular genetic testing is imperative to confirm CTD in newborns. Additionally, functional testing of fibroblast carnitine uptake remains necessary for cases in which other confirmatory testing is inconclusive. Even with utilization of all available diagnostic testing methods, confirmation of CTD ascertained by NBS remains lengthy and challenging. Incorporation of molecular analysis as a second tier step in NBS for CTD may be beneficial and should be investigated.
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Affiliation(s)
- N M Gallant
- Division of Genetic and Genomic Medicine, University of California, Irvine, Irvine, CA, United States; Department of Pediatrics, University of California, Irvine, Irvine, CA, United States; Stramski Children's Developmental Center, Miller Children's and Women's Hospital, Long Beach, CA, United States
| | - K Leydiker
- Division of Metabolic Disorders, Children's Hospital of Orange County, Orange, CA, United States
| | - Y Wilnai
- Lucile Packard Children's Hospital, Division of Medical Genetics, Stanford University Medical Center, Stanford, CA, United States
| | - C Lee
- Lucile Packard Children's Hospital, Division of Medical Genetics, Stanford University Medical Center, Stanford, CA, United States
| | - F Lorey
- Genetic Disease Screening Program, California Department of Public Health, Richmond, CA, United States
| | - L Feuchtbaum
- Genetic Disease Screening Program, California Department of Public Health, Richmond, CA, United States
| | - H Tang
- Genetic Disease Screening Program, California Department of Public Health, Richmond, CA, United States
| | - J Carter
- Genetic Disease Screening Program, California Department of Public Health, Richmond, CA, United States
| | - G M Enns
- Lucile Packard Children's Hospital, Division of Medical Genetics, Stanford University Medical Center, Stanford, CA, United States
| | - S Packman
- Division of Medical Genetics, Department of Pediatrics, University of California, San Francisco, San Francisco, CA, United States
| | - H J Lin
- Division of Medical Genetics, Department of Pediatrics, Harbor-UCLA Medical Center and Los Angeles Biomedical Research Institute, Torrance, CA, United States
| | - W R Wilcox
- Department of Human Genetics, Emory University School of Medicine, Atlanta, GA, United States
| | - S D Cederbaum
- Department of Psychiatry, David Geffen School of Medicine at UCLA, Los Angeles, CA, United States; Intellectual and Developmental Disabilities Research Center at UCLA, Los Angeles, CA, United States; Semel Institute for Neuroscience, UCLA, Los Angeles, CA, United States
| | - J E Abdenur
- Department of Pediatrics, University of California, Irvine, Irvine, CA, United States; Division of Metabolic Disorders, Children's Hospital of Orange County, Orange, CA, United States.
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