Researchers discovered that newborn screening (NBS) combined with genetic testing is critical to improving the screening efficiency of patients with primary carnitine deficiency (PCD), according to a study published in the Orphanet Journal of Rare Diseases.

“PCD is an autosomal recessive disorder of carnitine transportation that leads to impaired fatty acid oxidation,” Lin et al wrote. It is hence closely associated with long chain fatty acid oxidation disorder (LCFAOD). Many newborn screening tests include screening for PCD, as it is a treatable metabolic disease. 

While measuring carnitine transport activity is a reliable diagnostic assay for PCD, it is only performed in selected global laboratories and requires a skin biopsy. Therefore, genetic testing is largely used for diagnostic confirmation. 

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Epidemiological studies indicate that PCD is the most common fatty acid metabolic disorder in China. The authors of this study hence decided to investigate the efficacy of diagnosing PCD using NBS.

A total of 548,247 newborns were screened for PCD from January 2014 to June 2021 in Quanzhou, China. Of the 584,247 newborns, 1714 were reported to have low free carnitine levels, and 47 of them were diagnosed with PCD.

Notably, the NBS results indicated that the 49 patients diagnosed with PCD had various levels of decreased carnitine, while 7 had normal carnitine levels when recalled for a review. However, genetic testing indicated that all patients with PCD harbored biallelic pathogenic variants of the SLC22A5 gene. 

This study suggests that if NBS relies on carnitine levels alone for diagnosing PCD, some of the patients might be missed out, since carnitine levels may appear to be normal during the time of testing.

The ideal screening test for PCD is to measure carnitine levels in conjunction with genetic testing, the authors concluded.


Lin Y, Lin B, Chen Y, et al. Biochemical and genetic characteristics of patients with primary carnitine deficiency identified through newborn screeningOrphanet J Rare Dis. Published online December 4, 2021. doi:10.1186/s13023-021-02126-3