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  • Updated 02.20.2021
  • Released 11.28.1994
  • Expires For CME 02.20.2024

Carnitine-acylcarnitine translocase deficiency

Introduction

Overview

Carnitine-acylcarnitine translocase deficiency is a rare inborn error of energy metabolism involving the carnitine cycle. This enzyme deficiency is considered the most severe disorder of fatty acid oxidation. Its clinical features are related to the impairment of fasting adaptation and cardiac and skeletal muscle metabolism, and its presentation overlaps with the clinical presentation of the severe neonatal form of carnitine palmitoyltransferase type-2 deficiency. In this article, the author describes the developments of this disorder including the expanding clinical phenotype, the management, and the advances in the understanding of the genetics of this condition since the human gene was cloned in 1997.

Key points

Carnitine-acylcarnitine translocase deficiency shares clinical features with other defects of long-chain fatty acid oxidation.

The biochemical findings may be indistinguishable from the neonatal form of carnitine palmitoyltransferase type-2 deficiency.

The mortality rate is high and it occurs mainly in the first year of life.

In at least a quarter of cases, patients display mild manifestations with long-term survival.

Treatment consists of low-fat/high-carbohydrate diet and medium chain fat supplementation with frequent meals and avoidance of fasting.

Historical note and terminology

Carnitine-acylcarnitine translocase (CACT) deficiency is a rare defect in mitochondrial long-chain fatty acid oxidation and was first described in 1992 (27). Fatty acid oxidation is a critical energy source during fasting, and defects commonly result in life-threatening energy deficiency. The process of long chain fatty acid oxidation requires esterifying the fatty acid to coenzyme A (forming an acylCoA), then exchanging the CoA for carnitine (forming an acylcarnitine), after which the enzyme carnitine-acylcarnitine translocase transports the acylcarnitine into the mitochondria where oxidation and energy production occur. There are approximately a dozen defects in long-chain fat metabolism, and they share similar clinical features related to their impairment of fasting, cardiac functioning, and skeletal muscle metabolism (29).

This disorder is rare, with fewer than 100 cases reported. The majority of patients become symptomatic in the newborn period. The mortality rate reaches up to 65% in the first year of life due to cardiac complications (19). However, some patients have been described with a milder phenotype and long-term survival (28).

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