A fatty acid oxidation disorder (FAOD) is an “invisible” disease, meaning that patients with this diagnosis do not display characteristics that make it immediately obvious to those around them that they are ill. 

The challenge of living with a disease that is not readily apparent to others is that the patient is usually not afforded the space to navigate the challenges of living with the disease. This can add a psychological dimension to the illness in a way that can be extremely stressful to sufferers.

A Vague Presentation 

Let’s consider how FAODs first present themselves. In Reviews in Endocrine and Metabolic Disorders, Merritt and colleagues wrote, “Initial onset of FAOD may occur early or late in life and is characterized by a broad spectrum of clinical disease presentations, affecting a variety of high-energy–requiring organ systems, including the heart, liver, and skeletal muscle and nervous systems.” 

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The vague presentation of FAODs means that some patients do not get a proper diagnosis until much later in life. Symptoms can arise at any time from infancy on, and when they do occur, the lack of proper care can lead to life-threatening episodes of spontaneous acute decompensation. Merritt et al commented, “Clinical manifestations of disease can be serious, unpredictable, and precipitous in nature.” 

In addition, the mental impact of acute episodes can be devastating. These include mood swings, feelings of powerlessness, anxiety, and depression. 

So how do patients with a FAOD eventually get diagnosed? Since the onset of the disease varies greatly, a diagnosis is sometimes only suspected after serious symptoms manifest. Hence, there is a global movement advocating for FOAD testing to be included in newborn screening. The benefits of this approach are obvious: it allows for the disease to be detected quickly, efficiently, and (relatively) painlessly. 

Studies indicate that 50% of patients who are only diagnosed when symptomatic die from complications of the disease. Newborn screening allows physicians to prescribe appropriate lifestyle advice that can result in greatly improved outcomes. The management of FAOD generally encompasses dietary restrictions to minimize reliance on long-chain fatty acid catabolism. Nutritional advice can differ between patients, but the ultimate objective is to preserve the quality of life and prevent the onset of crises. 

The Patient Experience 

Despite the obvious toll that FAOD can have on patients, there is limited research on the patient experience. Williams-Hall and colleagues conducted a study to evaluate the quality of life impact of long chain FAODs (LCFAODs) because much of the existing publications focus solely on the clinical presentation, pathophysiology, and treatment of this type of disease. 

In a nod to the “invisible” nature of the disorder, Williams-Hall et al wrote in Therapeutic Advances in Endocrinology and Metabolism that “many of the features of LCFAOD are often clinician-read signs, symptoms, and complications.” The term “clinician-read” means that these symptoms tend to be only noticed by healthcare professionals and not the general population. 

Read more about LCFAOD etiology 

The research team conducted a 2.5-hour focus group with 4 LCFAOD patients and 4 caregivers in 2016. The discussion was semistructured and open-ended to ensure that all topics of interest were explored. In addition, the research team also interviewed 4 clinicians who treated patients with LCFAOD. 

The focus group found that patients typically experience acute crises once or twice per year, with some requiring hospitalization. Perceived triggers included fasting, prolonged exercise, and periods of acute illness. Patients reported the need to undergo significant lifestyle modifications to manage their disease, impacting their ability to function socially and physically, work, sleep, and carry out daily activities. A majority of participants also reported experiencing disturbances to their emotional/psychological well-being. 

The interviews with the clinicians also yielded interesting insights. Among the severe signs and symptoms of LCFAOD identified were cardiomyopathy, rhabdomyolysis, and hypoglycemia, which can lead to hospitalizations. The clinicians also revealed that impaired mobility and exercise intolerance were among the main functional limitations of patients with LCFAOD. 

The research team wrote, “Findings are consistent with what limited research has been conducted in this area and highlight that LCFAOD are serious, life-threatening conditions with substantial impacts on the functioning and [quality of life] of affected individuals.” 

The main limitations of this study are its small sample size and the known heterogeneous nature of LCFAOD clinical phenotypes. However, it is abundantly clear that many aspects of this disease are only noticeable to the patients and their clinicians, including many of the signs and symptoms, management strategies, and the psychological toll of living with this disease. 

Read more about LCFAOD complications 

On living with chronic disease, Voorhees wrote in Health Communication, “When faced with a serious injury or ongoing illness, individuals create an ‘illness identity’ by modifying their goals and expectations for the future, adapting to impairments, and understanding new emotional reactions.” In other words, patients with chronic illness often have to bend over backward in order to brave through life. 

The challenge for us physicians is to manage patients with FAOD with the care and dignity they deserve. If our patients sometimes feel “unseen” by society, it is our job to make sure that they feel seen and heard. We must not be afraid to ask tough questions during consultations and assure our patients of the physiological and psychological support they need. 


Merritt JL 2nd, MacLeod E, Jurecka A, Hainline B. Clinical manifestations and management of fatty acid oxidation disordersRev Endocr Metab Disord. 2020;21(4):479-493. doi:10.1007/s11154-020-09568-3

Williams-Hall R, Tinsley K, Kruger E, et al. Qualitative evaluation of the symptoms and quality of life impacts of long-chain fatty acid oxidation disordersTher Adv Endocrinol Metab. 2022;13:20420188211065655. doi:10.1177/20420188211065655

Voorhees HL. “I was literally just not myself”: how chronic pain changes multiple frames of identityHealth Commun. 2022;1-13. doi:10.1080/10410236.2022.2025702