Long-chain fatty acid oxidation disorders (LC-FAOD) are an autosomal recessive inherited rare disease group that result in an acute metabolic crisis and chronic energy deficiency owing to the deficiency in an enzyme that converts long-chain fatty acids into energy. LC-FAOD includes carnitine palmitoyltransferase type 1 (CPT1), carnitine-acylcarnitine translocase (CACT), carnitine palmitoyltransferase type 2 (CPT2), very long-chain acyl-CoA dehydrogenase (VLCAD), long-chain 3-hydroxyacyl-CoA dehydrogenase (LCHAD), and trifunctional protein (TFP) deficiencies. Common symptoms of LC-FAOD are hypoketotic hypoglycemia, cardiomyopathy, and myopathy. Depending on symptom onset, the disease can be divided as neonatal period, late infancy and early childhood, adolescence, or adult onset, but symptoms can appear at any time. The neonatal screening test (NBS) can be used to identify the characteristic plasma acylcarnitine profiles for each disease and confirmed by deficient enzyme analysis or molecular testing. Before introduction of NBS, the mortality rate of LC-FAOD was very high. With NBS implementation as routine neonatal care, the mortality rate was dramatically decreased, but severe symptoms such as rhabdomyolysis recur frequently and affect the quality of life. Triheptanoin (Dojolvi^®), the first drug for pediatric and adult patients with molecularly confirmed LC-FAOD, has recently been approved by the US Food and Drug Administration in 2020. In this review, the diagnosis of LC-FAOD and treatment including triheptanoin are summarized.

Glutaric aciduria type 1 (GA1; OMIM #231670) is a rare autosomal recessive inherited neurometabolic disorder caused by the deficiency of glutaryl-CoA dehydrogenase. Infantile-onset GA1 is the most common form characterized by striatal injury and progressive movement disorder, and it is often triggered by an acute encephalopathic crisis within the first three years of life. Once this crisis occurs, there is a high likelihood for ineffective or limited conventional interventions, neurological disorders, or even death. Therefore, early diagnosis and immediate preventive management, such as dietary therapy, is essential. In the past decades, newborn screening (NBS) by tandem mass spectrometry for GA1 has been largely introduced in many countries including Korea, and it has led to improvements in the neurological outcomes of patients with GA1. In this review, the clinical symptoms, natural histories, and outcomes before and after the introduction of NBS in patients are discussed.

The most common urea cycle disorder is ornithine transcarbamylase deficiency. More than 80 percent of patients with symptomatic ornithine transcarbamylase deficiency are late-onset, which can present various phenotypes from infancy to adulthood. With no regards to the severity of the disease, characteristic fluctuating courses due to hyperammonemia may develop unexpectedly, and can be precipitated by various metabolic stressors. Late-onset ornithine transcarbamylase deficiency is not merely related to a type of genetic variation, but also to the complex relationship between genetic and environmental factors that result in hyperammonemia; therefore, it is difficult to predict the prevalence of neurological symptoms in late-onset ornithine transcarbamylase deficiency. Most common acute neurological manifestations include psychological changes, seizures, cerebral edema, and death; subacute neurological manifestations include developmental delays, learning disabilities, intellectual disabilities, attention-deficit/hyperactivity disorder, executive function deficits, and emotional and behavioral problems. This review aims to increase awareness of late-onset ornithine transcarbamylase deficiency, allowing for an efficient use of biochemical and genetic tests available for diagnosis, ultimately leading to earlier treatment of patients.

Very long-chain acyl-coenzyme A dehydrogenase (VLCAD) deficiency (VLCADD) leads to a defective 𝛽-oxidation, specifically during prolonged fasting, infection, or exercise. Patients with VLCADD usually suffer from cardiomyopathy, hypoketotic hypoglycemia, hepatic dysfunction, exercise intolerance, muscle pain, and rhabdomyolysis, and sometimes succumb to sudden death. VLCADD is generally classified into three phenotypes: severe early-onset cardiac and multiorgan failure, hypoketotic hypoglycemia, and later-onset episodic myopathy. Diagnostic evaluation comprises acylcarnitine analysis, genetic analysis, and VLCAD activity assay. In the acylcarnitine analysis, the key metabolites are C14:1, C14:2, C14, and C12:1. A C14:1 level >1 mmol/L strongly suggests VLCADD. Various treatment recommendations are available for this condition. Dietary management includes decreasing fat content, increasing medium-chain triglyceride levels, and decreasing fasting periods. Supplementation with L-carnitine is controversial. Triheptanoin (a seven-carbon fatty acid triglyceride) treatment demonstrates improvement of cardiac functions. Bezafibrate may improve the quality of life of patients with VLCAD.

목적: 혈장 아미노산(PAA) 및 소변 유기산(UOA) 분석에서 비정상적인 대사 산물의 검출은 리 증후군과 같은 임상 미토콘드리아 질환을 진단하는 데 사용되었다. 본 연구에서는 PAA 및 UOA 분석의 진단적 가치와 유효성을 검토하였다. 방법: 이 논문은 2003년에서 2018년 사이에 단일 3차 진료 센터에서 진단된 리 증후군 환자에 대상으로 후향적 연구로 진행되었다. 전체 미토콘드리아 시퀀싱 및 핵 DNA 관련 미토콘드리아 유전자 패널 분석을 통해 미토콘드리아 DNA (mtDNA) 돌연변이 관련 리 증후군에 대해 19명의 환자가 양성이었고 57명의 환자는 음성인 것으로 밝혀졌다. 그 이후에 PAA 및 UOA 분석 결과를 비교하였다. 결과: 두 그룹 간의 PAA 및 UOA 분석 결과를 비교한 결과, mtDNA 돌연변이 양성 Leigh 증후군과 mtDNA 돌연변이 음성 Leigh 증후군 그룹 간에 비정상적인 대사 산물은 뚜렷한 차이를 보이지 않았다. 결론: PAA 및 UOA 분석은 리 증후군을 진단하거나 mtDNA 돌연변이 관련 리 증후군을 선별하기 위한 부적절한 검사 방법이다. 그러나 UOA 분석은 여전히 리 증후군에 대한 적합한 선별 검사일 수 있다.