Carnitine-acylcarnitine translocase deficiency: identification of a novel molecular defect in a Bedouin patient

Carnitine-acylcarnitine translocase deficiency: experience with four cases in Spain and review of the literature

BACKGROUND

Carnitine-acylcarnitine translocase (CACT) deficiency is a rare autosomal recessive disease in the mitochondrial transport of long-chain fatty acids. Despite early diagnosis and treatment, the disease still has a high mortality rate.

METHODS

Clinical symptoms, long-term follow-up, and biochemical and molecular results of four cases are described and compared with the reviewed literature data of 55 cases.

RESULTS

Two cases with neonatal onset, carrying in homozygosity the novel variant sequences p.Gly20Asp (c.59G>A) and p.Arg179Gly (c.536A>G), died during an intercurrent infectious process in the first year of life despite adequate dietetic treatment (frequent feeding, high-carbohydrate/low-fat diet, MCT, carnitine). The other two cases, one with infantile onset and the other diagnosed in the newborn period after a previous affected sibling, show excellent development at 4 and 16 years of age under treatment. The review shows that the most frequent presenting symptoms of CACT deficiency are hypoketotic hypoglycemia, hyperammonemia, hepatomegaly, cardiomyopathy and/or arrhythmia, and respiratory distress. The onset of symptoms is predominantly neonatal in 82% and infantile in 18%. The mortality rate is high (65%), most in the first year of life due to myocardiopathy or sudden death. Outcomes seem to correlate better with the absence of cardiac disease and with a higher long-chain fatty acid oxidation rate in cultured fibroblasts than with residual enzyme activity.

CONCLUSION

Diagnosis before the occurrence of clinical symptoms by tandem MS-MS and very early therapeutic intervention together with good dietary compliance could lead to a better prognosis, especially in milder clinical cases.

Expanded molecular features of carnitine acyl-carnitine translocase (CACT) deficiency by comprehensive molecular analysis

Carnitine-acylcarnitine translocase (CACT) deficiency is a rare autosomal recessive disease of fatty acid oxidation, mainly affecting long chain fatty acid utilization. The disease usually presents at neonatal period with severe hypoketotic hypoglycemia, hyperammonemia, cardiomyopathy and/or arrhythmia, hepatic dysfunction, skeletal muscle weakness, and encephalopathy. Definitive diagnosis of CACT deficiency by molecular analysis of the SLC25A20 gene has recently become clinically available. In contrast to biochemical analysis, sequence analysis is a more rapid and reliable method for diagnosis of CACT deficiency. In this study, we used Sanger sequencing and target array CGH to identify molecular defects in the SLC25A20 gene of patients with clinical features and an acylcarnitine profile consistent with CACT deficiency. Eight novel mutations, including a large 25.9 kb deletion encompassing exons 5 to 9 of SLC25A20 were found. Review of the published cases revealed that CACT deficiency is a pan-ethnic disorder with a broad mutation spectrum. Mutations are distributed along the entire gene without a hot spot. Two thirds of them are nonsense, frame-shift, or splice site mutations resulting in premature stop codons. This study underscores the importance of comprehensive molecular analysis, including sequencing and targeted array CGH of the SLC25A20 gene when CACT deficiency is suspected.

A novel SLC25A20 splicing mutation in patients of different ethnic origin with neonatally lethal carnitine-acylcarnitine translocase (CACT) deficiency

Carnitine-acylcarnitine translocase (CACT) deficiency is a rare disorder of fatty acid oxidation associated with high mortality. Two female newborns of different ethnic origin (the first Anglo-Celtic and the second Palestinian Arab) both died after sudden collapse on day 2 of life. Both had elevated bloodspot long-chain acylcarnitines consistent with either CACT or carnitine palmitoyltransferase II (CPT2) deficiency; the latter was excluded by demonstrating normal CPT2 activity in fibroblasts. Direct sequencing of all SLC25A20 (CACT) gene exons and exon-intron boundaries revealed that Patient 1 was compound heterozygous for a novel c.609-3c>g (IVS6-3c>g) mutation on the paternal allele and a previously described c.326delG mutation on the maternal allele. Patient 2 was homozygous for the same, novel c.609-3c>g mutation. Previously reported SLC25A20 mutations have been almost exclusively confined to a single family or ethnic group. Analysis of fibroblast cDNA by RT-PCR, agarose gel electrophoresis and sequencing of extracted bands showed that both mutations produce aberrant splicing. c.609-3C>G results in exon 7 skipping leading to a frameshift with premature termination seven amino acids downstream. c.326delG was confirmed to produce skipping of exons 3 or 3 plus 4. CACT activity in both patients' fibroblasts was near-zero. For both families, prenatal diagnosis of an unaffected fetus was performed by mutation analysis on CVS tissue in a subsequent pregnancy. Due to the urgency of prenatal diagnosis in the second family, molecular diagnosis was performed prior to demonstration of CACT enzyme deficiency, illustrating that mutation analysis is a rapid and reliable approach to first-line diagnosis of CACT deficiency.