[Clinical characteristics and genetic analysis of a child with Neutral lipid storage disease with myopathy].

OBJECTIVE: To explore the clinical phenotype and genetic basis of a child with Neutral lipid storage disease with myopathy (NLSDM). METHODS: A child who was admitted to the First Affiliated Hospital of Zhengzhou University in February 2021 for a history of elevated creatine kinase (CK) for over 2 months was selected as the study subject. Clinical and laboratory examinations were carried out, and the child was subjected to whole exome sequencing. Candidate variants were validated by Sanger sequencing of her family members. RESULTS: The patient, a 9-year-old female, had exhibited weakness in the lower limbs, elevated CK level, and refractory cardiomyotrophy. Genetic testing revealed that she has harbored c.32C>G (p.S11W) and c.516C>G (p.N172K) compound heterozygous variants of the PNPLA2 gene, which were respectively inherited from her mother and father. Based on the guidelines from the American College of Medical Genetics and Genomics (ACMG), both variants were rated as likely pathogenic (PM1+PM2_Supporting+PP3+PP4). CONCLUSION: The c.32C>G (p.S11W) and c.516C>G (p.N172K) compound heterozygous variants of the PNPLA2 gene probably underlay the myasthenia gravis and elevated creatine kinase in this child.

The Multifaceted Cause of Lipid Storage Myopathies, Genetics, and Treatment.

Several inherited metabolic fatty acid disorders present with myopathies. Skeletal muscle accounts for 40% of the body and is important for metabolism, exercise, and movement. Muscle energy failure is manifested by metabolic crises with muscle weakness, sometimes associated with muscle fatigue and failure resulting in acute necrosis or rhabdomyolysis/myoglobinuria episodes. Lack of energy leads to muscle necrosis. Other presentations are weakness and myalgias with lipid storage myopathies in the biopsy. The biomarkers of such disorders are acyl-carnitine with various profiles and need to be carefully evaluated to plan supplementary therapy and specific diets. If red flags are not distinctly followed and diagnosed in time they might lead to a metabolic or cardiac failure.

D-Bifunctional Protein Deficiency Diagnosis-A Challenge in Low Resource Settings: Case Report and Review of the Literature.

D-bifunctional protein deficiency (D-BPD) is a rare, autosomal recessive peroxisomal disorder that affects the breakdown of long-chain fatty acids. Patients with D-BPD typically present during the neonatal period with hypotonia, seizures, and facial dysmorphism, followed by severe developmental delay and early mortality. While some patients have survived past two years of age, the detectable enzyme activity in these rare cases was likely a contributing factor. We report a D-BPD case and comment on challenges faced in diagnosis based on a narrative literature review. An overview of Romania's first patient diagnosed with D-BPD is provided, including clinical presentation, imaging, biochemical, molecular data, and clinical course. Establishing a diagnosis can be challenging, as the clinical picture is often incomplete or similar to many other conditions. Our patient was diagnosed with type I D-BPD based on whole-exome sequencing (WES) results revealing a pathogenic frameshift variant of the HSD17B4 gene, c788del, p(Pro263GInfs*2), previously identified in another D-BPD patient. WES also identified a variant of the SUOX gene with unclear significance. We advocate for using molecular diagnosis in critically ill newborns and infants to improve care, reduce healthcare costs, and allow for familial counseling.

Tracing the lipidome in inborn errors of metabolism.

Inborn errors of metabolism (IEM) represent a heterogeneous group of more than 1800 rare disorders, many of which are causing significant childhood morbidity and mortality. More than 100 IEM are linked to dyslipidaemia, but yet our knowledge in connecting genetic information with lipidomic data is limited. Stable isotope tracing studies of the lipid metabolism (STL) provide insights on the dynamic of cellular lipid processes and could thereby facilitate the delineation of underlying metabolic (patho)mechanisms. This mini-review focuses on principles as well as technical limitations of STL and describes potential clinical applications by discussing recently published STL focusing on IEM.

Major clinical events and healthcare resource use among patients with long-chain fatty acid oxidation disorders in the United States: Results from LC-FAOD Odyssey program.

Major clinical events (MCEs) related to long-chain fatty acid oxidation disorders (LC-FAOD) in triheptanoin clinical trials include inpatient or emergency room (ER) visits for three major clinical manifestations: rhabdomyolysis, hypoglycemia, and cardiomyopathy. However, outcomes data outside of LC-FAOD clinical trials are limited. The non-interventional cohort LC-FAOD Odyssey study examines data derived from US medical records and patient reported outcomes to quantify LC-FAOD burden according to management strategy including MCE frequency and healthcare resource utilization (HRU). Thirty-four patients were analyzed of which 21 and 29 patients had received triheptanoin and/or medium chain triglycerides (MCT), respectively. 36% experienced MCEs while receiving triheptanoin versus 54% on MCT. Total mean annualized MCE rates on triheptanoin and MCT were 0.1 and 0.7, respectively. Annualized disease-related inpatient and ER events were lower on triheptanoin (0.2, 0.3, respectively) than MCT (1.2, 1.0, respectively). Patients were managed more in an outpatient setting on triheptanoin (8.9 annualized outpatient visits) vs MCT (7.9). Overall, this shows that those with LC-FAOD in the Odyssey program experienced fewer MCEs and less HRU in inpatient and ER settings during triheptanoin-treated periods compared with the MCT-treated periods. The MCE rate was lower after initiation of triheptanoin, consistent with clinical trials.

Recurrent familial case of early childhood sudden death: Complex post mortem genetic investigations.

INTRODUCTION: Sudden Unexplained Death in Childhood (SUDC) needs to be fully assessed considering its impact on the family, parents and siblings. Inborn Errors of Metabolism (IEM) such as Medium-Chain Acyl-CoA Dehydrogenase Deficiency (MCADD) should be taken into consideration when SUDC occurres. Our aim is to present a family with two successive SUDC and to discuss the post-mortem genetics investigations revealing an IEM implication. CASES REPORT: A complete autopsy with genetic testing was performed when the proband, a 4-year-old girl, died. A few years previously, her older brother had died at the same age and off the same condition. Years later, his exhumation was necessary in order to perform a post-mortem diagnosis.The two siblings were revealed to have had the same pathogenic genotype of the ACADM gene, heterozygous substitutions in ACADM (NM_000016.5): c.985 A>G p.(Lys329Glu) and c.347 G>A p.(Cys116Tyr). In addition, they also both carried a VUS in TECRL, a gene implicated in Catecholaminergic Polymorphic Tachycardia Ventricular (CPVT) and SUDC. CONCLUSION: We illustrate the importance of exome analyses for investigating unexplained sudden death, especially in children, with the possible impact for genetic counselling in the family. The finding of the implication of ACADM gene in this case, raises likely responsibility of the public health system in countries such as France, who delayed implementation of new born screening for these conditions. Exome analyses in this case detected unexpected complexity in interpretation linked to the identification of a second candidate gene for SUDC.

Sudden death with cardiac involvement in a neonate with carnitine-acylcarnitine translocase deficiency.

A female neonate born with normal Apgar scores at 38+2 weeks of gestational age unexpectedly passed away within less than 30 hours after birth. The situation mirrored her brother's earlier demise within 24 hours post-delivery, suggesting a possible genetic disorder. Gross examination revealed widespread cyanosis and distinct yellowish changes on the cardiac ventricles. Histopathological examination disclosed lipid accumulation in the liver, heart, and kidneys. Tandem mass spectrometry detected elevated levels of 10 amino acids and 14 carnitines in cardiac blood. Trio-whole genome sequencing (Trio-WGS) identified the SLC25A20 c.199-10T>G mutation associated with carnitine-acylcarnitine translocase disease (CACTD), a type of fatty acid oxidation disorders (FAODs) with a potential for sudden death. Further validation of gene expression confirmed the functional deficiency of SLC25A20, ultimately diagnosing CACTD as the underlying cause of the neonate's demise. This case highlights the importance of prenatal metabolic and genetic screening for prospective parents and emphasizes the need for forensic doctors to integrate metabolomic and genomic investigations into autopsies for suspected inherited metabolic diseases.

Platelet proteomic profiling in sitosterolemia suggests thrombocytopenia is driven by lipid disorder and not platelet aberrations.

ABSTRACT: Sitosterolemia is a rare autosomal recessive genetic disorder in which patients develop hypercholesterolemia and may exhibit abnormal hematologic and/or liver test results. In this disease, dysfunction of either ABCG5 or ABCG8 results in the intestinal hyperabsorption of all sterols, including cholesterol and, more specifically, plant sterols or xenosterols, as well as in the impaired ability to excrete xenosterols into the bile. It remains unknown how and why some patients develop hematologic abnormalities. Only a few unrelated patients with hematologic abnormalities at the time of diagnosis have been reported. Here, we report on 2 unrelated pedigrees who were believed to have chronic immune thrombocytopenia as their most prominent feature. Both consanguineous families showed recessive gene variants in ABCG5, which were associated with the disease by in silico protein structure analysis and clinical segregation. Hepatosplenomegaly was absent. Thrombopoietin levels and megakaryocyte numbers in the bone marrow were normal. Metabolic analysis confirmed the presence of strongly elevated plasma levels of xenosterols. Potential platelet proteomic aberrations were longitudinally assessed following dietary restrictions combined with administration of the sterol absorption inhibitor ezetimibe. No significant effects on platelet protein content before and after the onset of treatment were demonstrated. Although we cannot exclude that lipotoxicity has a direct and platelet-specific impact in patients with sitosterolemia, our data suggest that thrombocytopenia is neither caused by a lack of megakaryocytes nor driven by proteomic aberrations in the platelets themselves.

Family sitosterolemia: report of two cases in Colombia. / Sitosterolemia familiar: reporte de dos casos en Colombia.

Sitosterolemia is an autosomal recessive and very rare disease. Its main characteristic is that there is a greater absorption and a decrease in the excretion of sterols, which leads to them being deposited in tissues. It is given by mutations in the ABCG5 or ABCG8 genes found on chromosome 2p21. In this clinical note, we describe the first two patients with familial sitosterolemia described in Colombia, brothers, one of them with xanthomas in extremities as the only symptom, and the other, completely asymptomatic. Genetic studies were performed as a diagnostic test in both patients, where a pathogenic homozygous variant could be identified in the ABCG8 gene in the first case (symptomatic), and a heterozygous variant in the ABCG8 gene in the second case (asymptomatic); the first patient has responded to treatment with ezetimibe. In conclusion, xanthomas should be studied in depth in pediatric age as they may be the only visible sign of such complex and hereditary diseases as familial sitosterolemia, which can be controlled and prevent cardiovascular complications of the disease.

A review of fatty acid oxidation disorder mouse models.

Fatty acid oxidation disorders (FAODs) are a family of rare, genetic disorders that affect any part of the fatty acid oxidation pathway. Patients present with severe phenotypes, such as hypoketotic hypoglycemia, cardiomyopathy, and rhabdomyolysis, and currently manage these symptoms by the avoidance of fasting and maintaining a low-fat, high-carbohydrate diet. Because knowledge about FAODs is limited due to the small number of patients, rodent models have been crucial in learning more about these disorders, particularly in studying the molecular mechanisms involved in different phenotypes and in evaluating treatments for patients. The purpose of this review is to present the different FAOD mouse models and highlight the benefits and limitations of using these models. Specifically, we discuss the phenotypes of the available FAOD mouse models, the potential molecular causes of prominent FAOD phenotypes that have been studied using FAOD mouse models, and how FAOD mouse models have been used to evaluate treatments for patients.

Cardiac phenotype in adolescents and young adults with long-chain 3-hydroxyacyl CoA dehydrogenase (LCHAD) deficiency.

PURPOSE: Long-chain 3-hydroxyacyl-coenzyme A dehydrogenase deficiency (LCHADD) is a rare fatty acid oxidation disorder characterized by recurrent episodes of metabolic decompensation and rhabdomyolysis, as well as retinopathy, peripheral neuropathy, and cardiac involvement, such as infantile dilated cardiomyopathy. Because LCHADD patients are surviving longer, we sought to characterize LCHADD-associated major cardiac involvement in adolescence and young adulthood. METHODS: A retrospective cohort of 16 adolescent and young adult participants with LCHADD was reviewed for cardiac phenotype. RESULTS: Major cardiac involvement occurred in 9 of 16 participants, including sudden death, out-of-hospital cardiac arrest, acute cardiac decompensations with heart failure and/or in-hospital cardiac arrest, end-stage dilated cardiomyopathy, and moderate restrictive cardiomyopathy. Sudden cardiac arrest was more common in males and those with a history of infant cardiomyopathy. CONCLUSION: The cardiac manifestations of LCHADD in adolescence and early adulthood are complex and distinct from the phenotype seen in infancy. Life-threatening arrhythmia occurs at substantial rates in LCHADD, often in the absence of metabolic decompensation or rhabdomyolysis. The potential risk factors identified here-male sex and history of infant cardiomyopathy-may hint at strategies for risk stratification and possibly the prevention of these events.

A Clinical Case of Probable Sitosterolemia.

Sitosterolemia is a rare genetic lipid disorder characterized by elevated plant sterols in the serum. A 24-year-old Japanese woman was referred to our hospital due to a high serum low-density lipoprotein cholesterol (LDL-C) level of 332 mg/dL. At first, she was suspected to suffer from familial hypercholesterolemia, and thus received lipid-lowering agents. Although her LDL-C level remained high (220 mg/dL) with diet therapy plus 10 mg/day rosuvastatin, it was drastically decreased to 46 mg/dL with the addition of 10 mg/day ezetimibe. Finally, her LDL-C level was well-controlled at about 70 mg/dL with 10 mg/day ezetimibe alone. Furthermore, while her serum sitosterol level was elevated at 10.5 µg/mL during the first visit to our hospital, it decreased to 3.6 µg/mL with the 10 mg/day ezetimibe treatment alone. These observations suggest that she might probably suffer from sitosterolemia. Therefore, targeted gene sequencing analysis was performed using custom panels focusing on the exome regions of 21 lipid-associated genes, including ABCG5, ABCG8, and familial hypercholesterolemia-causing genes (LDL receptor, LDLRAP1, PCSK9, and apolipoprotein B). We finally identified a heterozygous ABCG8 variant (NM_022437.2:c.1285A>G or NP_071882.1:p.Met429Val) in our patient. The same gene mutation was detected in her mother. We report here a rare case exhibiting probable sitosterolemia caused by a heterozygous Met429Val variant in the ABCG8 gene and additional unknown variants.

Neutral lipid storage disease with myopathy: clinicopathological and genetic features of nine Iranian patients.

The rare disorder known as Neutral Lipid Storage Disease with Myopathy presents with a variety of clinical manifestations, including myopathy, cardiac dysfunction, and other organ complications. Early diagnosis is crucial due to the increased risk of cardiomyopathy. We describe the clinical, histopathological, muscle imaging, and genetic findings of nine neutral lipid storage myopathy patients. Proximal weakness and asymmetric involvement may suggest lipid storage myopathy. While skeletal muscle weakness was the main manifestation in our patients, one case presented only with hyperCKemia. Additionally, three patients had fertility issues, two suffered from diabetes mellitus, two had cardiomyopathy, and one had a history of hypothyroidism. Muscle histopathology revealed lipid depositions and rimmed vacuoles, prompting peripheral blood smears to detect Jordan Anomalies. All muscle biopsies and peripheral blood smear showed lipid droplets, rimmed vacuoles, and Jordan anomaly. Identifying PNPLA2 gene mutations is important for diagnosing neutral lipid storage myopathy; our cases showed some novel mutations. This study highlights the importance of early diagnosis and comprehensive evaluation in managing neutral lipid storage myopathy cases.

[Very-long chain acyl-coA dehydrogenase deficiency: report of a Chinese pedigree and a literature review].

OBJECTIVE: To explore the correlation between clinical classification and genotype and prognosis among Chinese children with Very-long chain acyl-CoA dehydrogenase deficiency (VLCADD). METHODS: A Chinese pedigree affected with VLCADD admitted at the First People's Hospital of Yunnan Province in February 2019 was selected as the study subject. The characteristics of disease onset, diagnosis and treatment and prognosis were retrospectively analyzed. Relevant literature was also systematically searched and reviewed. RESULTS: The proband, a 1-year-old boy, had the clinical manifestations of frequently vomiting, hypoglycemia, abnormal liver function and myocardial enzymes. Tandem mass spectrometry screening showed significantly elevated C14, C14:1, C16:1, C16:2, C18 and C14/C8. Genetic testing revealed that he has harbored compound heterozygous variants of the ACADVL gene, namely c.664G>A (p.G222R) and c.1345G>A (p.E449K), which were respectively derived from his father and mother. The child was diagnosed with VLCADD cardiomyopathy type and deceased 2 weeks later. Literature review has identified 60 Chinese children with VLCADD. The clinical classifications were mainly cardiomyopathy type and liver disease type, which accounted for 73.3% (43/60). The combination of ACADVL gene variants were correlated with the clinical classifications of VLCAD. Children with one or two loss-of-function (LOF) mutations showed more severe clinical manifestation and a higher mortality. Cardiomyopathy type had the poorest prognosis, with a mortality rate of 76.9% (20/26). C14:1 may be used as an indicator for the diagnosis of VLCADD, but cannot be used for clinical subtyping and prognosis evaluation. The c.1349G>A (p.R450H) variant had the highest frequency among the Chinese patients, accounting for 10.8% (13/120). CONCLUSION: The clinical classifications of VLCADD are strongly correlated with the prognosis, and LOF mutations are more common in those with severe clinical manifestations. c.1349G>A (p.R450H) may be the most common variant among the Chinese patients, and early screening and diagnosis can greatly improve the prognosis of patients.

Long-term monitoring of fatty acid oxidation defects: results from a MetabERN survey.

BACKGROUND: Implementation of long-chain fatty acid oxidation defects (LCFAOD) in newborn screening (NBS) programs allows for pre-symptomatic diagnosis and treatment. The long-term natural history of NBS LCFAOD patients is largely unknown and may differ from clinically diagnosed pre-NBS patients. This complicates long-term monitoring of LCFAOD and may cause high monitoring variability. To gain insight in current clinical practice, we performed a web-based questionnaire among all metabolic members of the European Reference Network for Hereditary Metabolic Disorders (MetabERN). RESULTS: Thirty-seven colleagues representing at least 35 European metabolic centres shared their experience and results were discussed at the European Metabolic Group (EMG) meeting 2022. The centres concurred in many aspects of long-term monitoring of LCFAOD including the frequency of clinical visits, determination of laboratory parameters, cardiac monitoring and retinopathy screening. Main discrepancies comprised hepatic imaging, glucose monitoring and electrophysiological investigations. CONCLUSIONS: Discrepancies may reflect differences in local availability of monitoring tools, the inclusion of LCFAOD in NBS programs as well as differences in local genotypes and phenotypes. Because monitoring strategies are largely based on the natural disease course of clinically identified patients, there might be over-monitoring of some NBS patients. Nevertheless, we advocate long-term monitoring because resulting information is essential to further characterize the natural disease course, develop evidence-based guidelines and provide a basis for evaluation of future therapies.

Chanarin-Dorfman Syndrome diagnosed at the stage of liver transplantation: A rare lipid storage disease.

Chanarin-Dorfman Syndrome (CDS) is a rare lipid storage disease with ichthyosis, hepatomegaly, myopathy, neuropathy, deafness, and ocular findings. Here, we aim to present an elderly CDS case and highlight the new endocrinological findings. A 66-year-old male patient with cirrhosis was hospitalized for liver transplantation. We suspected Chanarin-Dorfman Syndrome with ichthyosis, fatty liver, and syndromic facial features with bilateral ectropion, deafness, and malocclusion. We showed the lipid droplets in neutrophils called patognomonic Jordans' anomaly. Homozygous c.47+1 G>A mutation in the ABHD5 (NM_016006.6) gene were detected by clinical exome sequencing. Out of <160 CDS cases in the literature, this is the second eldest CDS patient and first with adrenal insufficiency, parathyroid lipoadenoma and atrophic pancreas. Clinicians should be aware of CDS as a rare cause of fatty liver. We recommend a blood smear and genetic analyses in patients with severe ichtiosis, ectropion, deafness and multiple endocrinolgic disorders.

Two novel heterozygous exonic deletions lead to Chanarin-Dorfman syndrome in a patient with congenital ichthyosis, sensorineural hearing loss, and liver dysfunction.

Chanarin-Dorfman syndrome is an autosomal recessively inherited disorder characterized by ichthyosis, sensorineural hearing loss, and hepatic dysfunction. We report on a 60-year-old female of Venezuelan descent who presented with congenital ichthyosis, progressive sensorineural hearing loss, and liver cirrhosis. We identify a heterozygous copy number deletion involving exon 1 and another heterozygous deletion involving exon 3 of the ABHD5 gene. Exon 2 is preserved. Both deletions were confirmed with RT-PCR. RNAseq from peripheral blood shows a reduction of ABHD5 expression overall and an absence of exon 3 expression, confirming the deleterious effects of the identified deletions. We present exonic deletions as a potentially common type of ABHD5 variation.

Structural insights into the pathogenicity of point mutations in human acyl-CoA dehydrogenase homotetramers.

Acyl-CoA dehydrogenase deficiency (ACAD) is an inherited and potentially fatal disorder with variable clinical symptoms. The relationship between pathogenicity and deleterious point mutations is investigated here in ACAD structures of short (SCAD) and medium-chain (MCAD) types. Structures and dynamic features of native and mutant forms of enzymes models were compared. A total of 2.88 µs molecular dynamics simulations were performed at four different temperatures. Total energy, RMSD, protein ligand interactions and affinity, RMSF measures, secondary structure changes, and important interactions were studied. Mutations in the three main domains of ACADs are pathogenic, while those located at linker turns are not. Mutations affect mostly tetramer formations, secondary structures, and many contacts and interactions. In R206H (MCAD mutant) which is experimentally known to cause a huge turnover decrease, the lack of a single H-bond between substrate and FAD was observed. Secondary structures showed temperature-dependent changes, and SCAD activity was found to be highly correlated to the enzyme helix 3-10 content. Finally, RMSF patterns pointed to one important loop that maintains the substrate close to the active site and is a cause of substrate wobbling upon mutation. Despite similar structure, function, and cellular location, SCAD and MCAD may have different optimum temperatures that are related to the structure taken at that specific temperature. In conclusion, new insight has been provided on the effect of various SCAD and MCAD pathogenic mutations on the structure and dynamical features of the enzymes.

[A case of very long chain acyl-CoA dehydrogenase deficiency diagnosed due to a trigger of hyperemesis gravidarum during pregnancy].

A 25-year-old Japanese woman with a history of repeated episodes of rhabdomyolysis since the age of 12 presented with rhabdomyolysis caused by hyperemesis gravidarum. Blood tests showed an elevated serum CK level (11,755 |IU/l; normal: 30-180 |IU/l). Carnitine fractionation analysis revealed low levels of total carnitine (18.3 |µmol/l; normal: 45-91 |µmol/l), free carnitine (13.1 |µmol/l; normal: 36-74 |µmol/l), and acylcarnitine (5.2 |µmol/l; normal: 6-23 |µmol/l). Tandem mass spectrometry showed high levels of C14:1 acylcarnitine (0.84 |nmol/ml: normal: <0.4 |nmol/ml) and a high C14:1/C2 ratio of 0.253 (normal: <0.013), indicating a potential diagnosis of very long-chain acyl-CoA dehydrogenase (VLCAD) deficiency. Enzyme activity measurement in the patient's peripheral blood lymphocytes confirmed the diagnosis of VLCAD deficiency, with low palmitoyl-CoA dehydrogenase levels (6.5% of normal control value). With the patient's informed consent, acyl-CoA dehydrogenase very long-chain (ACADVL) gene analysis revealed compound heterozygous mutations of c.1332G>A in exon 13 and c.1349G>A (p.R450H) in exon 14. In Japan, neonatal mass screening is performed to detect congenital metabolic diseases. With the introduction of tandem mass screening in 2014, fatty acid metabolism disorders, including VLCAD deficiency, are being detected before the onset of symptoms. However, it is important to note that mass screening cannot detect all cases of this disease. For patients with recurrent rhabdomyolysis, it is essential to consider congenital diseases, including fatty acid metabolism disorders, as a potential diagnosis.

Heptanoic and medium branched-chain fatty acids as anaplerotic treatment for medium chain acyl-CoA dehydrogenase deficiency.

Triheptanoin (triheptanoylglycerol) has shown value as anaplerotic therapy for patients with long chain fatty acid oxidation disorders but is contraindicated in medium-chain acyl-CoA dehydrogenase (MCAD) deficiency. In search for anaplerotic therapy for patients with MCAD deficiency, fibroblasts from three patients homozygous for the most common mutation, ACADMG985A/G985A, were treated with fatty acids hypothesized not to require MCAD for their metabolism, including heptanoic (C7; the active component of triheptanoin), 2,6-dimethylheptanoic (dMC7), 6-amino-2,4-dimethylheptanoic (AdMC7), or 4,8-dimethylnonanoic (dMC9) acids. Their effectiveness as anaplerotic fatty acids was assessed in live cells by monitoring changes in cellular oxygen consumption rate (OCR) and mitochondrial protein lysine succinylation, which reflects cellular succinyl-CoA levels, using immunofluorescence (IF) staining. Krebs cycle intermediates were also quantitated in these cells using targeted metabolomics. The four fatty acids induced positive changes in OCR parameters, consistent with their oxidative catalysis and utilization. Increases in cellular IF staining of succinylated lysines were observed, indicating that the fatty acids were effective sources of succinyl-CoA in the absence of media glucose, pyruvate, and lipids. The ability of MCAD deficient cells to metabolize C7 was confirmed by the ability of extracts to enzymatically utilize C7-CoA as substrate but not C8-CoA. To evaluate C7 therapeutic potential in vivo, Acadm-/- mice were treated with triheptanoin for seven days. Dose dependent increase in plasma levels of heptanoyl-, valeryl-, and propionylcarnitine indicated efficient metabolism of the medication. The pattern of the acylcarnitine profile paralleled resolution of liver pathology including reversing hepatic steatosis, increasing hepatic glycogen content, and increasing hepatocyte protein succinylation, all indicating improved energy homeostasis in the treated mice. These results provide the impetus to evaluate triheptanoin and the medium branched chain fatty acids as potential therapeutic agents for patients with MCAD deficiency.