For a neonate detected by newborn screening (NBS) with a potential diagnosis of very-long chain acyl-coA dehydrogenase deficiency (VLCAD), the most frequent evaluations for diagnostic confirmation include a combination of plasma acylcarnitine profile and molecular testing. Functional testing, including fibroblast acylcarnitine profiling and leukocyte or fibroblast enzyme assay, can be useful adjunct testing if uncharacterized variants are found and the diagnosis remains unclear.
Optimal VLCAD management requires ongoing assessment of clinical and nutritional status. Outcome measures from dietary history, anthropometrics, and clinical and laboratory assessment are used to determine appropriateness of treatment recommendations. Close monitoring of growth, development, and medical and nutrition parameters is needed for all individuals diagnosed with VLCAD. Evidence suggests that cardiac function should be monitored as part of routine care with more frequent evaluations in those with a severe form of VLCAD.
Consensus for routine monitoring of VLCAD is limited in both the formal and gray literature. However, after completing the Delphi survey and Nominal Group process, there was consensus (>80%) to routinely measure creatine kinase (CK) and plasma carnitine (total, ester, free) to assess severity and guide treatment recommendations, while comprehensive metabolic panel (liver enzymes and glucose), plasma acylcarnitine profile, essential fatty acid profile and cardiac monitoring would be used as conditional monitoring for patients.
Normal or near-normal concentrations of CK can be expected when individuals are asymptomatic. A CK concentration >1000 U/L can be used to define rhabdomyolysis and the extent of CK increase may be the best marker for severity of metabolic decompensation. Several sources suggest that monitoring plasma acylcarnitine profiles, specifically C14:1 and other long chain species with 14 to 18 carbons and the ratio of C14:1/C14, can be useful. Concentrations are expected to decrease with treatment and may be normal or near normal in those with a mild phenotype when asymptomatic. However, acylcarnitine concentrations can be influenced by length of fasting, dietary intake and carnitine supplementation and these factors need to be considered in interpretation of the results. Elevations in C8 and C10 acylcarnitines suggest MCT supplementation.
Monitoring of essential fatty acids (linoleic acid, α-linolenic acid), and their derivatives (arachidonic acid and docosahexaenoic acid) as well as fat-soluble vitamins is suggested to assess the need for dietary modification or supplementation for those treated with a fat-restricted diet.
Conduct nutrition assessments (dietary history, nutrient analysis, feeding skills and schedule, anthropometrics/growth, activity level and nutrition-related physical findings) to determine adherence and nutritional adequacy of a dietary prescription (RECOMMENDATION TABLE #10, Monitoring the Nutritional Management of an Individual with VLCAD when Well)
It is well established that nutrition assessment is an important component in the care of individuals with metabolic disorders (Y.31). Routine nutrition monitoring of patients should include anthropometrics, dietary intake and physical findings (G.128). When estimating energy needs for an individual, standard equations can be utilized (G.128). However, if a patient has a lower lean body mass (LBM) and higher fat mass, a lower activity factor may be useful. This has been recommended for patients with LCHAD and may not apply to other long-chain fatty acid oxidation disorders (LC-FAOD) (G.127).
Evaluate confirmatory testing (plasma acylcarnitine profile, genetic testing, enzyme testing) as it may suggest the severity of the disorder and can be helpful in guiding early nutrition management.
VLCAD deficiency can present at any age from the neonatal period to adulthood and poses the greatest risk of complications during intercurrent illness or after prolonged fasting. Early diagnosis, treatment, and surveillance can reduce morbidity and mortality; hence, the disorder is included in the newborn Recommended Uniform Screening Panel (RUSP) in the United States.
The Inborn Errors of Metabolism Information System (IBEM-IS) was established in 2007 to collect longitudinal information on individuals with inborn errors of metabolism included in NBS programs. A retrospective analysis of early outcomes for 52 individuals diagnosed with VLCAD by NBS (ages 1 to 18 years) found that plasma acylcarnitine profiles and molecular testing are the most common tests used to confirm the diagnosis. Functional testing (fibroblast acylcarnitine profiling and white blood cell or fibroblast enzyme assay) was useful to provide additional diagnostic information when uncharacterized mutations were identified (F.4055).
In 13 patients diagnosed prior to NBS, functional assays in fibroblasts (LC-FAO flux showed the strongest correlation) were found to be better predictors of VLCAD severity when compared to genotype analysis. LC-FAO flux was high even with low residual VLCAD enzyme activity - a residual activity of 20% was sufficient to allow normal rates of whole cell oxidation (F.4234).
A 1999 brief communication reported on data from 19 children with LC-FAOD and found that an acylcarnitine ratio of C14:1/C14 greater than 1, without elevated C10:1, was highly indicative of VLCAD deficiency in an acutely ill child (F.4383).
Confirmatory testing in other case reports or series included acylcarnitine profiles, genetic testing and/or enzyme testing (F.660, F.657, F.4128, F.4180, F.626, F.4383, F.633, F.4375, F.4406, F.4371,F.4422, F.7, F.8, F.10, F.2, F.3735, F.4424). Urine organic acids were used for diagnosis in two case reports (F.624, F.8) while another case study described organic acids as nondiagnostic (F.654).
A retrospective review of health records of 22 patients diagnosed with VLCAD deficiency by NBS and treated at one Australian center did not find a genotype-phenotype correlation to guide nutrition therapy for a specific patient (F.4375). The Background section of this guideline provides further details.
There was 100% consensus by MDs that plasma acylcarnitine profile, plasma carnitine (total, free, esters), CK, liver enzymes, glucose and cardiac evaluation should be a part of the confirmatory assessment to determine severity and guide management.
It was recommended that patients identified with a severe genotype be treated, even if asymptomatic.
There was 88% overall (MD/RD) consensus that confirmatory testing (plasma acylcarnitine profile, mutation analysis, enzyme testing) can suggest the severity of the disorder and help guide early nutrition management. However, one MD disagreed with this comment, noting that the above can only guide initial management. Another MD disagreed that acylcarnitine profile or enzyme testing reliably predicts disease severity.
Monitor creatine kinase and plasma carnitine profile (total, free, esters) for routine management of VLCAD.
Case reports of eight Chinese patients with confirmed VLCAD suggested that monitoring CK along with free carnitine, acylcarnitines and cardiac creatase was useful for management (F.3735). Normal concentrations of CK has been suggested as an indicator of treatment efficacy (F.3, F.660, F.626) and the extent of the increase in CK can be a useful marker for severity of metabolic derangement (F.657, F.633). However, others questioned the use of CK for routine monitoring, but reported its use for monitoring during rhabdomyolysis episodes with a CK >1000 uM used to define rhabdomyolysis (F.4055). CK increases during illness and correlates with increased acylcarnitines during these episodes (F.657). CK increased during accidental intake of a high fat diet (F.4), but did not increase with a fat load of 1.5 g/kg in an individual with a mild phenotype (F.3). In a neonate with possible VLCAD by NBS, elevated CK was noted before the onset of hypoglycemia (F.624). CK as high as 40,000 U/L was documented in an asymptomatic patient (F.654).
In a case report of an 8-year-old with VLCAD, an elevation of CK (20,000 U/L) was associated with severe muscle pain, but this was not noted until the day after 1 hour of soccer training. Supplementation of MCT before exercise reduced her adverse symptoms (F.7). Muscle MRI completed on 20 patients with LC-FAOD (including 12 with VLCAD) showed a correlation between CK values and muscle MRI Short-TI Inversion Recovery (STIR) scores (reflecting fatty infiltration of muscle tissue) suggesting that CK may be a useful marker for muscle weakness and/ or pain during metabolic episodes (F.4235). CK concentrations in patients without muscle symptoms ranged from 90 to 544 U/L, while CK in patients with muscle symptoms ranged from 35 to 11,180 U/L. The largely normal CK in those without muscle symptoms and higher concentrations in those with symptoms supported reserving CK monitoring for symptomatic patients.
Elevations of CK often first develop in patients when they are 1 to 3 years of age. Thus,practitioners should be alert for elevated CK and the potential for rhabdomyolysis in the toddler years (F.4055).
In a practice survey, 89% of MDs in Canada suggest use of CK for routine treatment monitoring (F.661).
There was 88% overall consensus (RD/MD) that CK, as a measure of chronic and acute muscle injury, is useful to evaluate the effectiveness of an asymptomatic individual's treatment regimen.
75% of RDs and 80% of MD indicated that CK should be routinely monitored.
Carnitine plays an important role in formation of long-chain acylcarnitines to allow transport of long-chain fatty acids across the mitochondrial membrane for β-oxidation. Low concentrations of plasma carnitine (total, free, esterified) have been measured in VLCAD (F.4422,F.17, F.3, F.633, F.657) and supplementation has been used to restore or maintain normal concentrations (F.2, F.17, F.633, F.660, F.4415).
Surveys have documented the use of plasma carnitine concentrations as an indicator of the extent of endogenous acylcarnitine formation in unsupplemented patients (F.3) and as an indicator for the need for L-carnitine supplementation (F.2).
59% of physicians in Canada recommended routine monitoring of carnitine concentrations (F.661). Day-to-day variation in carnitine concentrations from one subject was 10.7% for free carnitine and 14.6% for the acylcarnitine fraction (F.4128).
See further evidence summarized in recommendation 3.1.1
90% of MDs and 70% of RDs indicated that plasma carnitine (total, free and ester fractions) should be routinely monitored.
Consider additional monitoring when indicated by special circumstances, which may include comprehensive metabolic panel, acylcarnitine profile, essential fatty acids, fat soluble vitamins, cardiac monitoring and other biochemical markers (RECOMMENDATION TABLE #10, Monitoring the Nutritional Management of an Individual with VLCAD when Well)
Liver enzymes: Elevations in liver transaminases (AST, ALT) can provide evidence of hepatomegaly and fatty liver (F.4422, F.9). Increased liver enzymes are associated with muscle pain with excessive physical activity (F.633) and prolonged poor energy intake (F.629). In child with cardiomyopathy, CK and AST increased during illness and correlated with the increase in acylcarnitine concentrations (F.657).
83% of metabolic physicians in Canada suggested routine monitoring of liver enzymes (F.661), while the results of a published Delphi survey suggested that liver enzymes are indicated when an affected child is ill or at risk for a metabolic crisis (F.9). Liver enzymes remained normal with a fat load of 1.5 g/kg in an individual with a mild phenotype (F.3).
Glucose: Hypoglycemia was a frequently reported complication during metabolic episodes (F.624, F.4415, F.4, F.8, F.629, F.4180, F.626, F.4234,F.633, F.4055, F.4406). 72% of Canadian physicians recommended routine monitoring of glucose concentrations. These physicians suggested that following glucose, along with CK, liver enzymes and nutritional status is more important for routine monitoring than monitoring metabolites associated with VLCAD (acylcarnitine profile, urine organic acids, urine acylglycines) (F.661).
75% of RDs and 60% of MDs indicated that a CMP should be routinely monitored for asymptomatic individuals with VLCAD.
Several papers suggest that acylcarnitine profiles can be useful for routine monitoring (F.3, F.4, F.10, F.626, F.3735, F.4415), including acylcarnitine profiles in dried blood spots (F.657). In a study using plasma samples from children with defects of LC-FAOD, the C14:1/C14 acylcarnitine ratio ranged from 0.13 to 0.52 in five asymptomatic individuals with VLCAD, and from 0.88 to 4.62 in ten symptomatic individuals, compared to <0.1 for normal controls (F.4383).
The acylcarnitines C14 and C14:1 decreased with diet treatment (reduced long-chain fat (LCF) diet and MCT supplementation) and were associated with improved symptoms (F.10). Long-chain acylcarnitine concentrations decreased after a meal and increased after exercise on diets containing either C8 or C7 fatty acids (F.4424). Concentrations of long- chain acylcarnitines were lower when walnut or flaxseed oil was used to provide essential fatty acids compared to canola oil - C14:1 was 35% lower, C16 was 22% lower and C18:1 was 39% lower on the diet supplemented with flax/walnut oil (F.4415). Plasma C8:0 and C10:0 acylcarnitines were increased with MCT supplementation (F.17).
C.14:1 can be low secondary to systemic carnitine deficiency (F.4415). For patients with normal free carnitine concentrations, there does not appear to be a correlation between free carnitine and the sum of long-chain acylcarnitines (G.135).
In a practice survey, 59% of physicians from Canada suggested including plasma acylcarnitine profiles in routine monitoring of individuals with VLCAD (F.661).
The sum of acylcarnitines has been recommended to evaluate metabolic control in individuals with VLCAD. The equation is C14:0 + C14:1 + C14:2 +C16:0 + C16:1 + C18:0 + C18:1 + C18:2, with a total of <2 umol/L suggesting good metabolic control (G.135, G.28, G.128).
The nominal group concluded that acylcarnitine profiles may not be the best indicator of a patient's metabolic control since results can be influenced by fasting, dietary intake, carnitine supplementation and health status. If these variables are not well-controlled, the acylcarnitine profile may not truly reflect a patient's dietary control. Therefore, an acylcarnitine profile should not be considered a primary indicator to guide nutrition management.
Consensus was not reached that an acylcarnitine profile should not be used as a primary indictor to guide nutrition management, although 75% of RDs and 70% of MDs agreed with this statement. One RD commented that she consistently observes improved acylcarnitine profiles (based on the sum of very-long chain species: C14:0+C14:1+C14:2+C16:0+C16:1+C18:0) with better adherence to diet. One MD stated that monitoring acylcarnitine profiles can help identify patients who are not compliant with their treatment regimen. Another RD added that timing of lab draws for acylcarnitine profiles need to be consistent and not taken when ill.
When treated with a low-fat diet, patients with VLCAD may experience low blood levels of linoleic acid (LA), alpha linolenic acid (ALA), arachidonic acid (ARA) and docosahexaenoic acid (DHA) (F.2, F.8, F.4375), as well as an abnormal Holman ratio (i.e. triene:tetraene ratio) (F.633). Retrospective data for 75 patients (32 with VLCAD) in European centers showed that monitoring plasma fatty acid concentrations can identify patients needing treatment for essential fatty acid deficiency (F.2).
Essential fatty acids should be monitored for deficiency by evaluating absolute values from a fatty acid profile. The Holman ratio may not indicate essential fatty acid deficiency since it does not account for omega-3 fatty acid status. Absolute values should include LA, ALA, ARA and DHA (G.133).
Cardiac function should be monitored periodically as part of routine follow-up for individuals with VLCAD. Electrocardiogram (ECG) (F.4234, F.633, F.3, F.626, G.142) and echocardiogram (F.626, F.4234, F.633, F.4055, F.4422, F.17) were the most frequently assessed measures of cardiac function. Echocardiogram monitoring was recommended yearly, even for those without signs of cardiac dysfunction (F.3). Cardiac creatase was measured in one case study (F.660). In a longitudinal study of 52 individuals with VLCAD diagnosed by NBS, ECG and echocardiogram monitoring was routinely used in the newborn period (F.4055).
For patients at risk for the severe infantile phenotype, cardiac monitoring included troponin concentrations, cardiac evaluation and ECG (F.9). Cardiac troponin and brain natriuretic peptide (BNP), along with other metabolic laboratory measurements were monitored in a woman with VLCAD who developed heart failure in the post-partum period (F.3816).
Conditional monitoring for cardiac status:
90% of MDs and 81% of RDs recommend conditional monitoring of B-type natriuretic peptide (BNP).
80% of MDs and 75% of RDs recommend conditional monitoring of troponin.