Three Novel and One Potential Hotspot CPT1A Variants in Chinese Patients With Carnitine Palmitoyltransferase 1A Deficiency

Abstract

Carnitine palmitoyltransferase 1A (CPT1A) deficiency is an inherited disorder of mitochondrial fatty acid β-oxidation that impairs fasting ketogenesis and gluconeogenesis in the liver. Few studies implementing newborn screening (NBS) for CPT1A deficiency in the Chinese population have been reported. This study aimed to determine the biochemical, clinical, and genetic characteristics of patients with CPT1A deficiency in China. A total of 204,777 newborns were screened using tandem mass spectrometry at Quanzhou Maternity and Children's Hospital between January 2017 and December 2018. Newborns with elevated C0 levels were recruited, and suspected patients were subjected to further genetic analysis. Additionally, all Chinese patients genetically diagnosed with CPT1A deficiency were reviewed and included in the study. Among the 204,777 screened newborns, two patients were diagnosed with CPT1A deficiency; thus, the estimated incidence in the selected population was 1:102,388. In addition to the two patients newly diagnosed with CPT1A deficiency, we included in our cohort 10 Chinese patients who were previously diagnosed. Five of these 12 patients were diagnosed via NBS. All patients exhibited elevated C0 and/or C0/(C16+C18) ratios. No clinical symptoms were observed in the five patients diagnosed via NBS, while all seven patients presented with clinical symptoms, including fever, cough, vomiting, diarrhea, and seizures. Eighteen distinct CPT1A variants were identified, 15 of which have been previously reported. The three novel variants were c.272T>C (p.L91P), c.734G>A (p.R245Q), and c.1336G>A (p.G446S). in silico analysis suggested that all three novel variants were potentially pathogenic. The most common variant was c.2201T>C (p.F734S), with an allelic frequency of 16.67% (4/24). Our findings demonstrated that NBS for CPT1A deficiency is beneficial. The three novel variants expand the mutational spectrum of CPT1A in the Chinese population, and c.2201T>C (p.F734S) may be a potential hotspot CPT1A mutation.

Keywords: CPT1A gene; carnitine palmitoyltransferase 1A deficiency; in silico prediction; newborn screening; tandem mass spectrometry.

Figure 1

Overview of all CPT1A variants found in the Chinese population.

Figure 2

Multiple sequence alignment using ClustalX. Alignment of the CPT1A sequences revealed that the amino acid residues at positions 91, 245, and 446 (highlighted in box) were strictly conserved.

Figure 3

Three-dimensional structural modeling of wild-type and mutant CPT1A proteins. The yellow dashed lines represent hydrogen bonds, and the red numbers represent the hydrogen bond distances. Leu-91 is located in the extracellular segment between two transmembrane domains. The p.L91P variant may affect the quaternary structure of CPT1A by causing the loss of the side chain hydrogen bond with Thr-90, which may result in abnormal folding of CPT1A. p.R245Q is located in the C-terminal catalytic domain, which may affect the quaternary structure of CPT1A by eliminating the side chain hydrogen bonds with Gly-244, Gly-319, and Asp-323, possibly resulting in abnormal folding. p.G446S is located in the C-terminal catalytic domain; the beta turn in the CPT1A secondary structure was changed to a random coil, resulting in an unstable protein.