长链脂肪酸氧化障碍（LC-FAOD）诊断、治疗与监测国际指南。
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摘要 长链脂肪酸氧化障碍（LC-FAOD）是线粒体β氧化罕见的遗传性缺陷，在禁食或代谢应激期间损害能量生成。临床表现从新生儿低酮性低血糖和心肌病到肝病、复发性横纹肌溶解和慢性肌病。尽管新生儿筛查（NBS）能够早期发现，但由于证据有限、表型谱扩大以及地区实践差异，管理仍不一致。一个由34名成员组成的国际多学科工作组，包括临床医生、护士、营养师和患者代表，使用PubMed、Embase和Web of Science系统回顾了1990年至2022年的文献。证据采用改编的推荐分级评估、制定与评价（GRADE）方法进行分级，并通过改良的德尔菲-名义小组-德尔菲方法达成共识，共识定义为≥75%。尤其在证据质量低时，专家共识是本指南的基础。建议涉及诊断、饮食管理、禁食耐受性、中链脂肪来源的使用、运动和疾病方案、妊娠护理以及长期监测。证据质量从极低到中等不等。对关键临床干预措施达成了强烈共识。制定了诊断检查、代谢应激期间管理和随访监测的标准化方法，以促进不同年龄组、疾病组和表型严重程度之间的统一护理。本国际指南整合 利用可获得的证据和专家共识，为LC-FAOD的诊断、治疗和终身管理提供标准化建议。它们旨在协调临床实践、改善患者预后，并支持全球实施循证代谢护理。 缩略语 妊娠期急性脂肪肝 β-羟丁酸 肉碱-酰基肉碱转位酶 肌酸激酶 肉碱棕榈酰转移酶 二十二碳六烯酸 膳食营养素参考摄入量 体外膜肺氧合 射血分数 必需脂肪酸 视网膜电图 眼底自发荧光 推荐意见分级的评估、制定与评价 溶血、肝酶升高和血小板减少 遗传性代谢病 静脉注射 长链脂肪 长链脂肪酸氧化障碍 长链3-羟酰基辅酶A脱氢酶 左心室 新生儿筛查 鼻胃 光学相干断层扫描 经皮内镜下胃造口术 生活质量 三羧酸 三功能蛋白 视觉诱发电位 极长链酰基辅酶A脱氢酶 长链脂肪酸氧化障碍（LC‐FAOD）是一组遗传性代谢疾病（IMD），其特征是线粒体中长链脂肪酸的β‐氧化受损，而β‐氧化对于能量产生至关重要，尤其是在禁食或能量需求增加时期。这些缺陷源于编码参与肉碱循环和β‐氧化途径的酶和转运蛋白的基因致病性变异。本指南涉及的长链脂肪酸氧化障碍包括：肉碱棕榈酰转移酶1a（CPT1a）缺乏症（OMIM #255120; ORPHA:156），肉碱‐酰基肉碱转位酶（CACT）缺乏症（OMIM #212138; ORPHA:159），肉碱棕榈酰转移酶2（CPT2）缺乏症（OMIM #255110, #600649, #608836; ORPHA:157），极长链酰基辅酶A脱氢酶（VLCAD）缺乏症（OMIM #201475; ORPHA:26793），长链3‐羟基酰基辅酶A脱氢酶（LCHAD）缺乏症（OMIM #609016; ORPHA:5），以及线粒体三功能蛋白（TFP/MTP）缺乏症（OMIM #609015; ORPHA:746）。 临床上，LC-FAOD（长链脂肪酸氧化障碍）表现出广泛的表型谱，从产前畸形到出生后最初几天的急性代谢危象（包括低酮性低血糖、心肌病、心律失常、横纹肌溶解和高氨血症），再到后期的慢性进行性肌无力、肝病、心律失常、肌病、神经病变或劳力性横纹肌溶解。具有极轻度酶缺乏的个体以及通过基于人群的新生儿筛查（NBS）发现的新生儿可能终生无症状，或仅在代谢应激较高时期（如疾病、禁食、活动增加、环境温度极端变化以及心理/情绪应激）出现症状。 临床表现的变异性给早期诊断和管理带来了挑战。新生儿筛查（NBS）的进展改善了早期检测，使得能够及时干预，从而减轻某些严重后果。这也导致了表型谱的拓宽，尤其是对于某些疾病如极长链酰基辅酶A脱氢酶（VLCAD）缺乏症，进一步使诊断和管理模式复杂化。在此方面，将晚发型疾病与携带者状态区分开来仍然存在挑战，并且存在将具有生化异常但无临床症状的新生儿视为患者进行医疗化和不必要治疗的风险。当前的治疗策略侧重于禁食时长和饮食调整，并补充中链脂肪来源以绕过缺陷通路。患病日管理计划和终末器官疾病监测至关重要。然而，由于高质量证据有限以及诊断和治疗资源可及性的差异，实践差异仍然存在。更具挑战性的是针对通过新生儿筛查（NBS）发现的日益增多的无症状或轻症个体的治疗策略。 鉴于长链脂肪酸氧化障碍（LC-FAOD）的罕见性、异质性和复杂性，迫切需要标准化的临床实践指南，以优化照护、降低发病率和死亡率，并改善患者的生存质量（QOL）。本指南采用基于证据和共识的方法制定，供参与LC-FAOD患者诊断和照护的代谢专科医生、儿科医生、新生儿科医生、重症监护专家、成人内科医生、神经科医生、营养师、妇科医生、护士、心理医生、检验科专家和药师使用。它综合现有证据和专家共识，为LC-FAOD患者在整个生命周期的诊断、治疗和长期监测提供标准化建议，支持全球范围内一致、高质量的医疗服务。 方法与目标 本项目工作组由34名成员组成，包括医生、护士、营养师以及一名患者/家属代表。工作组成员分为三组（诊断与监测、治疗、长期并发症）。每组设两名联合主席。工作组联合主席确定了研究问题并制定了检索词。 文献检索 检索在三个数据库中进行：PubMed、Embase 和 Web of Science。初次检索于2020年7月执行，覆盖日期范围自1990年1月1日至2020年7月1日。2022年7月进行了一次补充检索更新，日期范围为2020年7月1日至2022年7月1日。检索策略的详细信息（包括检索词）见File 。此外，通过专家知识确定了15篇文章和2个书籍章节，这些内容未被初始检索策略捕获。纳入文献列表见File 。系统综述和荟萃分析首选报告条目（PRISMA）流程图见Figure 。 PRISMA流程图，用于在LC‐FAOD指南制定过程中进行的文献综述。 文献综合与初步推荐意见的制定 工作组成员使用改良版GRADE方法学对文章质量进行了评估 [, , ]。针对每个研究问题撰写了证据摘要，并起草了初步推荐意见。主席根据现有证据为每条推荐意见指定了强度，使用以下定义： “弱”推荐意味着现有证据质量可疑（极低或低），或者高质量研究（中等或高）显示某种方法相对于另一种方法几乎没有明显优势。 A “一般”推荐意味着工作组认为益处超过危害（或者在负面推荐的情况下危害明显超过益处），但证据质量没那么强（中等）。在某些明确指出的情况下，当高质量证据不可用时，可以基于较低质量的证据提出推荐，且预期益处超过危害。 A “强”推荐意味着工作组认为所推荐方法的益处明显超过危害（或者在强烈负面推荐的情况下危害明显超过益处），且支持证据的质量为优/良好（高）。在某些明确指出的情况下，当高质量证据无法获得时，可以基于较少的证据提出强推荐，且预期益处强烈超过危害。 每条推荐意见的强度采用改良的GRADE框架进行分配，该框架基于益处与危害的平衡、证据质量以及效应估计的确定性 [, ]。 最终推荐的制定 推荐意见由工作组成员审阅，并采用德尔菲-名义群体-德尔菲方法最终确定 []。德尔菲调查和名义群体投票采用五点李克特量表（非常不同意、不同意、中立、同意或非常同意）进行。共识定义为75%或以上的参与者表示同意或非常同意。 德尔菲调查数据是根据埃默里大学机构审查委员会（IRB）批准的方案（方案编号 #00009134）收集的。 指南 诊断 在症状性病例中，在无症状病例新生儿筛查（NBS）阳性时以及无症状病例确诊后，应进行哪些临床和实验室检查？ 对于出现提示 LC‐FAOD 症状的患者，或通过新生儿筛查阳性、家族筛查或偶然发现（例如通过选择性代谢筛查或基因组合检测）而发现疑似 LC‐FAOD 的无症状个体，目前缺乏关于最佳初始临床和实验室检查的可靠证据。虽然缺乏更大规模的研究，但大量已发表的关于 LC‐FAOD 患者的病例报告和病例系列研究展示了患者有发生各种临床症状和实验室异常的风险。 症状性病例中的诊断性检查 LC‐FAOD 患者可在 NBS 结果回报之前出现症状和生化异常 [, ]。在 LC‐FAOD 患者中，早在出生后 24 小时即可观察到低血糖、乳酸酸中毒和/或 CK 的相关升高。伴有心肌病、呼吸窘迫和高氨血症的有症状 TFP 缺乏症患者在出生第一天即可观察到。在 CPT2 缺乏症最严重的表现中，脑和肾畸形及心肌病可在产前明显可见 []。晚发型病例也可表现为横纹肌溶解或神经病变（MTPD/LCHADD）。在这种情况下，有症状病例的基线评估见表 。 LC‐FAOD 患者的推荐临床和实验室评估。 注：X = 推荐。(X) = 可选。— = 不推荐。 另见章节 和 。 许多机构表示使用酰基肉碱谱来评估游离肉碱。 如果分子结果不明确，或为严重程度评估所需。 如果怀疑 LCHADD/TFPD（非新生儿期进行）。 如果怀疑 CACTD 或新生儿型 CPT2 缺乏症，否则根据临床指征。 如果因横纹肌溶解或在严重 CPT2 或 CACT 缺乏症中怀疑肾功能障碍，考虑：血尿素氮、肌酐和/或胱抑素 C 以及肾小管功能标志物。 尽管在大多数长链脂肪酸氧化障碍（LC‐FAOD）病例中，心脏症状很常见，但心脏受累并非CPT1缺乏症或晚发型肌病型CPT2缺乏症的临床特征，尤其是由c.338C>T变异引起的CPT2缺乏症。因此，CPT1缺乏症和肌病型CPT2缺乏症患者无需进行心脏检查。 通过新生儿血斑筛查发现的病例中的诊断性检测 首要目的是确定患者的生理状态，判断其是否代谢稳定，或者是否存在明显或即将发生的代谢失代偿或器官受累的证据。基线检查见表。基线评估不仅确立诊断，而且有助于监测疾病进展和潜在治疗的效果。 用于确认（或排除）诊断的靶向诊断性生化、遗传和/或功能检测，如第节和第节中的建议所述。LC‐FAOD的新生儿血斑筛查（NBS）假阳性结果可能发生，应通过随访检测予以识别[，]。多篇文献报道，部分NBS异常的婴儿随后酰基肉碱谱正常[，，]。据报道，NBS假阳性和假阴性结果可通过酶/功能检测和/或分子遗传学检测来解决[，，，，，，]。 尸检和产前检测 长链脂肪酸氧化缺陷（LC-FAOD）已被报道为婴儿猝死综合征（SIDS）和急性危及生命事件（ALTE）的病因之一 []，但解读死后收集的酰基肉碱谱可能具有挑战性。遗传学检查可提供明确信息，特别是对于计划生育和遗传咨询。 存在携带LC-FAOD胎儿风险的妊娠（通常因先前有患病子女而识别）有数种诊断选择 []。可选检测包括羊水酰基肉碱谱分析，或针对已知家族基因型的羊水细胞或胎盘分子检测。参见产前诊断部分。或者，等待婴儿分娩并进行脐带血酰基肉碱检测，或更好的是在婴儿24小时龄内获取婴儿样本，只要新生儿留在婴儿室，定期喂养和监测直到获得结果，都是合适的。注意，脐带血中的诊断性代谢物可能因母体循环的清除而仅轻度异常或缺失。 建议： 无论临床情况如何，都应对疑似患有LC-FAOD的患者进行适当的临床和实验室评估。可能的检测项目数量众多，列于表中。初始临床评估应针对神经、肝脏和心脏功能，而实验室评估应包括生化参数以及器官功能筛查，包括肝脏、心脏和肌肉参数。 证据质量：低。 推荐强度：强。 在（貌似）无症状但新生儿筛查（NBS）结果阳性的新生儿中，标准诊疗是进行额外的生化和临床检查，包括功能检测。随访检测也将识别出NBS的假阳性结果。 证据质量：低。 推荐强度：强。 对于有症状提示长链脂肪酸氧化障碍（LC-FAOD）的新生儿，除NBS外还需进行选择性代谢筛查。 证据质量：低。 推荐强度：强。 受累个体的高危家庭成员应接受临床评估和检测，以明确可能的LC-FAOD。 证据质量：低。 推荐强度：强。 在婴儿猝死综合征（SIDS）或明显危及生命事件（ALTE）的背景下，应考虑LC-FAOD。 证据质量：低。 推荐强度：强。 应进行分子遗传学检测。 证据质量：低。 推荐强度：强。 产前诊断有哪些可用且推荐的方法？ 在过去，产前诊断一直基于生化和酶学技术，但最近，胎儿DNA的遗传学分析已成为标准做法[]。在已确定潜在分子缺陷的家庭中，遗传学产前检测是首选方法。当遗传学结果不明确（例如，发现意义不明的变异）或无法获得时，生化和/或酶学分析可用作替代或补充方法。在某些情况下，例如CPT2缺乏症，酰基肉碱分析的灵敏度不足以对代谢缺陷做出可靠的产前诊断[]。 关于产前诊断的个人、文化和伦理价值观的考虑超出了本指南的范围，这些方面应在个体基础上与家属讨论。 推荐： 建议将分子遗传学分析用于长链脂肪酸氧化障碍（LC‐FAOD）的产前诊断。 证据质量：极低。 推荐强度：强。 评估严重程度的最佳工具有哪些？ “疾病严重程度”这一术语在文献中的定义不一致。在本指南中，疾病严重程度指症状的频率和强度。理想情况下，评估患者的疾病严重程度有助于更好地进行个体化管理并预测临床病程。关于该主题的文献量仍相对较少，但已有多种工具可用于量化疾病严重程度。 除一些例外情况，大多数疾病的基因型/表型相关性难以预测，包括LC-FAOD。CPT2中常见的c.338C>T (p.Ser113Leu)变异通常与成人起病的轻度表型相关，而导致功能失活的变异则导致严重的新生儿型[，，，]。LCHAD缺乏症由常见HADHA变异c.1528G>C (p.Glu510Gln)的纯合性引起；然而，尽管存在遗传同质性，LCHAD缺乏症患者的临床表型可能高度可变。在TFP缺乏症中，位于蛋白质外环的致病性变异（预计对蛋白质稳定性影响较小）通常与轻度疾病相关[]。临床表现的严重程度也与硫解酶抗原减少的程度相关[]。在VLCAD缺乏症中，有证据表明由错义变异（尤其是蛋白质C末端）导致的病例表型较轻。c.848T>C (p.V283A)变异是在VLCADD NBS阳性个体中发现的最常见致病性变异[]。它通常与青春期或成年早期的横纹肌溶解症发病相关，而与心肌病无关。在CACT缺乏症中，最常见的致病性剪接位点变异c.199-10T>G的纯合性与严重的新生儿起病型疾病相关[]。 测量FAO酶活性也有帮助，尽管其可用性在地理上受限，且通常仅在研究基础上提供。在淋巴细胞或成纤维细胞中测得的VLCAD酶活性（棕榈酰-CoA氧化）水平与临床表型相关[,,,]。残余酶活性>20%符合轻症/晚发型疾病，甚至终身无症状；酰基肉碱谱仍可异常[]。细胞LC-FAO通量的测量已显示与VLCADD患者的临床严重程度相关[]。将VLCADD患者来源的成纤维细胞与标记的棕榈酸一起孵育，产生两种不同的酰基肉碱种类谱，分别与伴有肥厚型心肌病的严重早发型疾病和主要表现为低酮性低血糖的轻症疾病直接相关。
全文（开放获取） · 英文原文
【Abstract】 Long-chain fatty acid oxidation disorders (LC-FAOD) are rare inherited defects of mitochondrial β-oxidation that impair energy generation during fasting or metabolic stress. Clinical manifestations range from neonatal hypoketotic hypoglycemia and cardiomyopathy to hepatopathy, recurrent rhabdomyolysis, and chronic myopathy. Although newborn screening (NBS) enables early detection, management remains inconsistent due to limited evidence, broadening phenotypic spectrum, and regional practice variation. An international multidisciplinary workgroup of 34 members, including clinicians, nurses, dietitians, and patient representatives, systematically reviewed the literature (1990-2022) using PubMed, Embase, and Web of Science. Evidence was graded using an adapted Grading of Recommendations Assessment, Development, and Evaluation (GRADE) approach, and consensus was achieved through a modified Delphi-Nominal Group-Delphi methodology, with agreement defined as ≥ 75%. Especially when evidence was low, expert consensus was the basis for this guideline. Recommendations address diagnosis, dietary management, fasting tolerance, use of medium-chain fat sources, exercise and illness protocols, pregnancy care, and long-term monitoring. Evidence quality ranged from very low to moderate. Strong consensus was reached for critical clinical interventions. Standardized approaches for diagnostic work-up, management during metabolic stress, and follow-up monitoring were developed to promote uniform care across age groups, disease groups, and phenotypic severity. This international guideline integrates available evidence and expert consensus to provide standardized recommendations for diagnosis, treatment and lifelong management of LC-FAOD. They aim to harmonize clinical practice, improve patient outcomes, and support global implementation of evidence-based metabolic care. 【Abbreviations】 acute fatty liver of pregnancy beta‐hydroxybutyrate carnitine‐acylcarnitine‐translocase creatine kinase carnitine palmitoyltransferase docosahexaenoic acid dietary reference intakes extracorporeal membrane oxygenation ejection fraction essential fatty acid electroretinogram fundus autofluorescence Grading of Recommendations Assessment, Development, and Evaluation hemolysis, elevated liver enzymes, and low platelet count inherited metabolic disorders intravenous long‐chain fat long‐chain fatty acid oxidation disorders long‐chain 3‐hydroxyacyl‐CoA dehydrogenase left ventricular newborn screening nasogastric optical coherence tomography percutaneous endoscopic gastrostomy quality of life tricarboxylic acid trifunctional protein visual evoked potential very long‐chain acyl‐CoA dehydrogenase 【Introduction】 Long‐chain fatty acid oxidation disorders (LC‐FAOD) are a group of inherited metabolic disorders (IMD) characterized by impaired mitochondrial β‐oxidation of long‐chain fatty acids, essential for energy production, particularly during periods of fasting or increased energy demand. These defects result from pathogenic variants in genes encoding enzymes and transport proteins involved in the carnitine cycle and β‐oxidation pathway. LC‐FAOD addressed in this guideline are: carnitine palmitoyltransferase 1a (CPT1a) deficiency (OMIM #255120; ORPHA:156), carnitine‐acylcarnitine‐translocase (CACT) deficiency (OMIM #212138; ORPHA:159), carnitine palmitoyltransferase 2 (CPT2) deficiency (OMIM #255110, #600649, #608836; ORPHA:157), very long‐chain acyl‐CoA dehydrogenase (VLCAD) deficiency (OMIM #201475; ORPHA:26793), long‐chain 3‐hydroxyacyl‐CoA dehydrogenase (LCHAD) deficiency (OMIM #609016; ORPHA:5), and mitochondrial trifunctional protein (TFP/MTP) deficiency (OMIM #609015; ORPHA:746). Clinically, LC‐FAOD manifest with a broad phenotypic spectrum ranging from prenatal malformations to acute metabolic crises in the first days of life—including hypoketotic hypoglycemia, cardiomyopathy, cardiac arrhythmias, rhabdomyolysis, and hyperammonemia—to chronic, progressive muscle weakness, hepatopathy, cardiac arrhythmias, myopathy, and neuropathy or exertional rhabdomyolysis in later life. Individuals with very mild enzyme deficiencies and newborns identified through population‐based newborn screening (NBS) can remain asymptomatic throughout life or develop symptoms only during periods of high metabolic stress (e.g., illness, fasting, increased activity, environmental temperature extremes, and psychological/emotional stress). The variability in clinical presentation poses challenges for early diagnosis and management. Advances in NBS have improved early detection, enabling prompt intervention that can mitigate some severe outcomes. It has also led to a broadening of the phenotypic spectrum, particularly for some conditions such as VLCAD deficiency, further complicating the diagnostic and management paradigm. Here, challenges remain in differentiating late‐onset disease from carrier status, with a risk of medicalizing and unnecessarily treating newborns with biochemical abnormalities but not clinical symptoms as patients. Current therapeutic strategies focus on fasting duration and dietary modifications, with supplementation of medium‐chain fat sources to bypass defective pathways. Sick day management plans and monitoring for end‐ organ disease are critical. However, practice variation persists due to limited high‐quality evidence and differences in access to diagnostic and therapeutic resources. Even more challenging are treatment strategies in the increasing number of asymptomatic or mildly affected individuals identified by NBS. Given the rarity, heterogeneity, and complexity of LC‐FAOD, there is a pressing need for standardized clinical practice guidelines to optimize care, reduce morbidity and mortality, and improve quality of life (QOL) for affected individuals. This guideline, developed with evidence‐ and consensus‐based methodology, is intended to be used by metabolic specialists, pediatricians, neonatologists, intensive care specialists, adult physicians, neurologists, dietitians, gynecologists, nurses, psychologists, laboratory specialists, and pharmacists involved in the diagnosis and care of LC‐FAOD patients. It synthesizes available evidence and expert consensus to provide standardized recommendations for diagnosis, treatment, and long‐term monitoring of patients with LC‐FAOD across the lifespan, supporting consistent, high‐quality care worldwide. 【Methodology and Objectives】 The workgroup for this project was comprised of 34 members, including physicians, nurses, dietitians, and a patient/family representative. The workgroup members were divided into three groups (Diagnosis & Monitoring, Treatment, and Long‐term Complications). Two co‐chairs were assigned to each group. The workgroup co‐chairs defined the research questions and identified search terms. 【Literature Search】 Searches were performed in three databases: PubMed, Embase, and Web of Science. The initial searches were performed in July 2020 and covered the date range from January 1, 1990, through July 1, 2020. An additional search update was performed in July of 2022 that had a date range of July 1, 2020, through July 1, 2022. Details of the search strategy, including search terms, are available in File . In addition, 15 articles and 2 book chapters were identified through expert knowledge that was not captured by the initial search strategy. A list of included literature is available in File . The Preferred Reporting Items for Systematic Reviews and Meta‐Analyses (PRISMA) flowchart is presented in Figure . PRISMA flow diagram chart for the literature review conducted as part of the development of the LC‐FAOD guideline. 【Literature Synthesis and Development of Preliminary Recommendations】 Workgroup members assessed the quality of the articles using the modified GRADE methodology [, , ]. Evidence summaries were drafted for each research question, and preliminary recommendations were drafted. The chairs assigned a strength to each recommendation based on the available evidence, using the following definitions: A “Weak” recommendation means that the quality of evidence that exists is suspect (very low or low) OR that well‐done studies (moderate or high) show little clear advantage to one approach versus another. A “Fair” recommendation means that the workgroup believes that the benefits exceed the harms (or that the harms clearly exceed the benefits in the case of a negative recommendation), but the quality of evidence is not as strong (moderate). In some clearly identified circumstances, recommendations can be made based on lower‐quality evidence when high‐quality evidence is not available, and the anticipated benefits outweigh the harms. A “Strong” recommendation means that the workgroup believes that the benefits of the recommended approach clearly exceed the harms (or that the harms clearly exceed the benefits in the case of a strong negative recommendation), and that the quality of the supporting evidence is excellent/good (high). In some clearly identified circumstances, strong recommendations can be made based on lesser evidence when high‐quality evidence is impossible to obtain, and the anticipated benefits strongly outweigh the harms. The strength of each recommendation was assigned using a modified GRADE framework based on the balance of benefits and harms, quality of evidence, and certainty in effect estimates [, ]. 【Development of Final Recommendations】 The recommendations were reviewed by the workgroup members and finalized using a Delphi‐Nominal Group‐Delphi methodology []. Delphi surveys and Nominal Group voting were conducted using a five‐point Likert scale (strongly disagree, disagree, neutral, agree, or strongly agree). Consensus was defined as 75% or more of participants indicating agreement or strong agreement. The Delphi survey data were collected under a protocol approved by the Emory University Institutional Review Board (IRB) (protocol #00009134). 【Guideline】 【Diagnosis】 【What Clinical and Laboratory Work‐Up Should be Performed (in Symptomatic Cases, at Time of Positive NBS in Asymptomatic Cases and After Confirmation of the Disease in Asymptomatic Cases)?】 There is a lack of robust evidence for the optimal initial clinical and laboratory work‐up in patients with symptoms suggestive of LC‐FAOD or in asymptomatic individuals with suspected LC‐FAOD who were identified through positive NBS, through family screening or incidentally (e.g., through selective metabolic screening or genetic panel investigations). While larger‐scale studies are absent, the plethora of published case reports and series on LC‐FAOD patients illustrates the wide spectrum of clinical symptoms and laboratory abnormalities patients are at risk of developing. 【Diagnostic Tests in Symptomatic Cases】 LC‐FAOD patients can present with symptoms and biochemical abnormalities prior to the return of NBS results [, ]. In LC‐FAOD patients, hypoglycemia, lactic acidosis, and/or relevant elevations of CK have been observed as early as 24 h after birth. Symptomatic TFP deficiency patients with cardiomyopathy, respiratory distress, and hyperammonemia have been observed on the first day of life. In the most severe presentation of CPT2 deficiency, cerebral and renal malformations and cardiomyopathy can be evident prenatally []. Later onset cases can also present with rhabdomyolysis or neuropathy (MTPD/LCHADD). In such cases, baseline evaluation for symptomatic cases is indicated in Table . Recommended clinical and laboratory assessment for individuals with LC‐FAOD. Note: X = recommended. (X) = optional. — = not recommended. See also Sections and . Many institutions indicated use of acylcarnitine profile to assess free carnitine. If molecular results are unclear, or if necessary for severity assessment. If LCHADD/TFPD is suspected (do it in other than in neonate). If CACTD or neonatal form of CPT2 deficiency is suspected, otherwise at clinical indication. If renal dysfunction is suspected because of rhabdomyolysis or in severe CPT2 or CACT deficiency, consider: blood urea nitrogen, creatinine and/or cystatin C along with markers of tubular function. Although cardiac symptoms are common in most cases of LC‐FAOD, cardiac involvement is not a clinical feature of CPT1 deficiency or the late‐onset myopathic form of CPT2 deficiency, especially caused by the c.338C>T variant. Therefore, individuals with CPT1 and myopathic CPT2 deficiencies do not require cardiac investigations. 【Diagnostic Tests in Cases Identified by Newborn Bloodspot Screening】 Primarily, the aim is to ascertain the patient's physiological status, discerning whether they are metabolically stable or if there is evidence of manifest or impending metabolic decompensation or organ involvement. Baseline investigations are indicated in Table . A baseline assessment not only establishes a diagnosis but also facilitates monitoring of disease progression and efficacy of potential treatments. Targeted diagnostic biochemical, genetic, and/or functional testing to confirm (or exclude) diagnosis are as described in the recommendations in sections and . False positive NBS results for LC‐FAOD occur and should be identified by follow‐up testing [, ]. Several publications report normal subsequent acylcarnitine profiles in infants with an abnormal NBS [, , ]. False positive and negative NBS results have been reported to be addressed by enzyme/functional assays and/or molecular genetic testing [, , , , , , ]. 【Post‐Mortem and Prenatal Testing】 LC‐FAOD have been reported as a cause for sudden infant death syndrome (SIDS) and acute life‐threatening events (ALTE) [], but the interpretation of acylcarnitine profiles collected post‐mortem can be challenging. Genetic investigations provide clarification, specifically for family planning and genetic counseling. Pregnancies at risk for carrying a fetus with an LC‐FAOD (typically identified because of a prior affected child) have several options for diagnosis []. Optional testing includes amniotic fluid acylcarnitine profiling or amniocyte or placental molecular testing for a known familial genotype. See Section for prenatal diagnosis. Alternatively, waiting for delivery of the baby and acylcarnitine testing on cord blood, or preferably a sample from the baby by 24 h of age, is appropriate as long as the neonate remains in the nursery, is fed and monitored regularly until the results are available. Note that diagnostic metabolites in cord blood could be minimally abnormal or absent due to clearance by the maternal circulation. Recommendations: Appropriate clinical and laboratory evaluation should be performed in patients suspected of having a LC‐FAOD regardless of the clinical circumstances. The number of possible tests is large and listed in Table . Initial clinical assessments should address neurological, hepatic, and cardiac function, while the laboratory evaluation should include biochemical parameters as well as organ function screening, including liver, heart, and muscle parameters. Quality of evidence: low. Strength of recommendation: strong. In (apparently) asymptomatic newborns with positive NBS, the standard of care is to conduct additional biochemical and clinical investigations, including functional testing. Follow‐up testing will also identify false‐positive NBS results. Quality of evidence: low. Strength of recommendation: strong. In neonates with symptoms suggestive of LC‐FAOD, selective metabolic screening is required in addition to NBS. Quality of evidence: low. Strength of recommendation: strong. At‐risk family members of an affected individual should have clinical assessment and testing for possible LC‐FAOD. Quality of evidence: low. Strength of recommendation: strong. LC‐FAOD should be considered in the context of SIDS or ALTE. Quality of evidence: low. Strength of recommendation: strong. Molecular genetic testing should be performed. Quality of evidence: low. Strength of recommendation: strong. 【What Methods Are Available and Recommended for Prenatal Diagnostics?】 In the past, prenatal diagnostics has been based on biochemical and enzymatic techniques, but more recently, genetic analysis of fetal DNA has become the standard of care []. In families in whom the underlying molecular defect has been established, genetic prenatal testing is the method of choice. Biochemical and/or enzymatic analyses can be used as alternative or additional methods when genetic results are inconclusive (e.g., identification of variants of unknown significance) or unavailable. In some cases, e.g., CPT2 deficiency, acylcarnitine analysis is not sensitive enough to enable a reliable prenatal diagnosis of the metabolic defect []. The consideration of individual, cultural, and ethical values regarding prenatal diagnostics is beyond the scope of this guideline, and these aspects should be discussed with the family on an individual basis. Recommendation: Molecular genetic analysis is recommended for the prenatal diagnosis of LC‐FAOD. Quality of evidence: very low. Strength of recommendation: strong. 【What Are the Best Tools for Severity Assessment?】 The term disease severity is inconsistently defined in the literature. For the purposes of this guideline, disease severity refers to the frequency and intensity of symptoms. Ideally, assessing disease severity in a patient enables better individualized management and prediction of the clinical course. The body of literature on this topic is still relatively scarce, but several tools exist that are of use in quantifying disease severity. With some exceptions, genotype/phenotype correlations for most diseases are difficult to predict, including for LC‐FAOD. The common c.338C>T (p.Ser113Leu) variant in CPT2 is usually associated with an adult‐onset mild phenotype, while inactivating variants result in a severe neonatal form [, , , ]. LCHAD deficiency is caused by homozygosity for the common HADHA variant c.1528G>C (p.Glu510Gln); however, despite genetic homogeneity, the clinical phenotype of individuals with LCHAD deficiency can be highly variable. In TFP deficiency, pathogenic variants in the outer protein loops, which are expected to have less impact on protein stability, are usually associated with mild disease []. The severity of the clinical presentation is also correlated with the degree of reduction in thiolase antigen []. In VLCAD deficiency, evidence suggests milder phenotypes in cases caused by missense variants, especially in the C‐terminus of the protein. The c.848T>C (p.V283A) variant is the most frequent pathogenic variant found in individuals with a positive VLCADD NBS []. It is usually associated with onset of rhabdomyolysis in adolescence or early adulthood and not cardiomyopathy. In CACT deficiency, homozygosity for the most common pathogenic splice site variant c.199‐10T>G is associated with a severe neonatal‐onset form of the disease []. Measurement of FAO enzyme activities is also helpful, though availability is geographically limited and often available only on a research basis. The level of VLCAD enzyme activity (palmitoyl‐CoA oxidation) measured in lymphocytes or fibroblasts correlates with clinical phenotype [, , , ]. Residual enzyme activity > 20% is consistent with mild/late‐onset disease or even lack of symptoms throughout life; the acylcarnitine profile can still be abnormal []. Measurement of cellular LC‐FAO flux has been shown to correlate with the clinical severity of VLCADD patients []. Incubation of VLCADD patient‐derived fibroblasts with labeled palmitate produces two distinct profiles of acylcarnitine species that directly correlate with severe early‐onset disease with hypertrophic cardiomyopathy and mild disease manifesting primarily as hypoketotic hypoglycemia