Molecular investigation in Chinese patients with primary carnitine deficiency

Abstract

Background: Primary carnitine deficiency (PCD) is an autosomal recessive disorder of carnitine transportation caused by mutations in the SLC22A5 that lead to low serum carnitine levels and decreased intracellular carnitine accumulation. Characteristic clinical findings are hypoketotic hypoglycemia and skeletal and cardiac myopathy.

Objective: To genetically diagnose 24 unrelated Chinese patients with PCD, including 18 infants and six adults.

Methods: The entire coding region and the intron-exon boundaries of SLC22A5 were amplified by polymerase chain reaction (PCR). In silico analyses and reverse transcription-polymerase chain reaction (RT-PCR) were used to predict variants' impact on protein structure and function.

Results: Disease-causing variants in the SLC22A5 were identified in all 24 subjects, and c.288delG, c.495C>A, c.774_775insTCG, c.824+1G>A, and c.1418G>T were novel. The novel variant c.824+1G>A caused a truncated protein p.Phe276Tyrfs*8.

Conclusions: We identified 13 variants in the SLC22A5 in 24 PCD patients, and five of these variants are novel mutations. c.824+1G>A was confirmed to alter mRNA splicing by reverse transcription PCR. Furthermore, our findings broaden the mutation spectrum of SLC22A5 and the understanding of the diverse and variable effects of PCD variants.

Keywords: newborn screening; primary carnitine deficiency; splice site mutation; variant.

Figure 1

Result of reverse transcription PCR of c.824+1G>A. The variant caused the first 13 bases of intron 3 being included into the coding sequence to form a frameshift of p.Phe276Tyrfs*8

Figure 2

Schematic of the OCTN2 carnitine transporter with location of variants identified in this study. Positions of functional domains are based on the information provided by the Universal Protein Resource (UniProt) (http://www.uniprot.org/)