Carnitine-acylcarnitine translocase deficiency (CACTD) is an autosomal recessive disorder affecting the carnitine-acylcarnitine translocase (CACT), which plays a pivotal role in mitochondrial fatty acid oxidation (FAO). This deficiency results from mutations in the SLC25A20 gene on chromosome 3p21.31, encompassing 9 exons and encoding 301 amino acids[1]. 42 mutation sites of this gene have been noted to be pathogenic in the Human Gene Mutation Database (HGMD). These variations primarily involve missense and deletion, impacting the activity of CACT, thereby reducing the transport of long-chain fatty acid into mitochondria[2].

CACTD was initially documented in 1992[3]. It exhibits a relatively low prevalence, varying across populations due to genetic heterogeneity. Among the Chinese population, estimated incidences include 1/100,000 in Guangdong[4], 1/76,894 in Hunan[5], and 1/60,000 in Hong Kong[6]. In contrast, estimated incidences only range from 1/750,000 to 1/2,000,000 in the Caucasian population[7]. CACTD clinically manifests as metabolic decompensation, cardiomyopathy, hepatopathy, and myopathy[2]. Symptoms typically emerge in the neonatal period, characterized by rapid deterioration and a high mortality rate. Its rarity of incidence and the diversity of its clinical manifestations make diagnosis challenging, often requiring specialized biochemical and molecular testing to confirm. Up to now, there is still no consensus clinical criteria for CACTD[8].

This case confirms CACTD as the underlying cause of death in a Chinese family's second child, shedding light on the undetected genetic metabolic disorder leading to neonatal sudden death.