Molecular and functional analysis of SLC25A20 mutations causing carnitine-acylcarnitine translocase deficiency.
The enzyme carnitine-acylcarnitine translocase (CACT) is involved in the transport of long-chain fatty acids into mitochondria. CACT deficiency is a life-threatening, recessively inherited disorder of lipid beta-oxidation which manifests in early infancy with hypoketotic hypoglycemia, cardiomyopathy, liver failure, and muscle weakness. We report here the clinical, biochemical, and molecular features of six CACT-deficient patients from Italy, Spain, and North America who exhibited significant clinical heterogeneity. In five patients (Patients 1, 2, 4, 5, and 6) the disease manifested in the neonatal period, while the remaining patient (Patient 3), the younger sibling of an infant who had died with clinical suspicion of fatty acid oxidation defect, has been treated since birth and was clinically asymptomatic at 4.5 years of age. Patients 1 and 4 were deceased within 6 months from the onset of this study, while the remaining four are still alive at 8, 4.5, 3.5, and 2 years, respectively. Sequence analysis of the CACT gene (SLC25A20) disclosed five novel mutations and three previously reported mutations. Three patients were homozygous for the identified mutations. Two of the novel mutations (c.718+1G>C and c.843+4_843+50del) altered the donor splice site of introns 7 and 8, respectively. The 47-nt deletion in intron 8 caused both skipping of exon 8 only and skipping of exons 6-8. Four mutations [[c.159dupT;c.163delA] ([p.Gly54Trp;p.Thr55Ala]) c.397C>T (p.Arg133Trp), c.691G>C (p.Asp231His), and c.842C>T (p.Ala281Val)] resulted in amino acid substitutions affecting evolutionarily conserved regions of the protein. Interestingly, one of these exonic mutations (p.Ala281Val) was associated with a splicing defect also characterized by skipping of exons 6-8. The deleterious effect of the p.Arg133Trp substitution was demonstrated by measuring CACT activity upon expression of the normal and the mutant protein in E. coli and functional reconstitution into liposomes. Combined analysis of clinical, biochemical, and molecular data failed to indicate a correlation between the phenotype and the genotype.
Iacobazzi
Vito
V
Laboratory of Biochemistry and Molecular Biology, Department of Pharmaco-Biology, University of Bari, Bari, Italy.
Invernizzi
Federica
F
Baratta
Silvia
S
Pons
Roser
R
Chung
Wendy
W
Garavaglia
Barbara
B
Dionisi-Vici
Carlo
C
Ribes
Antonia
A
Parini
Rossella
R
Huertas
Maria Dolores
MD
Roldan
Susana
S
Lauria
Graziantonio
G
Palmieri
Ferdinando
F
Taroni
Franco
F
D000595:Amino Acid Sequence; D019943:Amino Acid Substitution; D002333:Carnitine Acyltransferases / Q000737:chemistry / Q000172:deficiency* / Q000235:genetics / Q000502:physiology; D002675:Child, Preschool; D004252:DNA Mutational Analysis; D004926:Escherichia coli; D005091:Exons / Q000235:genetics; D017809:Fatal Outcome; D005227:Fatty Acids / Q000378:metabolism; D005260:Female; D005808:Genes, Recessive; D018740:Genetic Heterogeneity; D005838:Genotype; D006801:Humans; D007231:Infant, Newborn; D007438:Introns / Q000235:genetics; D007558:Italy; D008052:Lipid Metabolism, Inborn Errors / Q000453:epidemiology / Q000235:genetics*; D008297:Male; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000172:deficiency* / Q000235:genetics / Q000502:physiology; D008928:Mitochondria / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation; D020125:Mutation, Missense; D009656:North America; D010084:Oxidation-Reduction; D017354:Point Mutation; D022821:RNA Splice Sites / Q000235:genetics; D011993:Recombinant Fusion Proteins / Q000502:physiology; D017384:Sequence Deletion; D013030:Spain; D013329:Structure-Activity Relationship
D005227:Fatty Acids; D026901:Membrane Transport Proteins; D022821:RNA Splice Sites; D011993:Recombinant Fusion Proteins; C120109:SLC25A20 protein, human; D002333:Carnitine Acyltransferases