Metabolic phenotyping in phenylketonuria reveals disease clustering independently of metabolic control.

Phenylketonuria (PKU, MIM #261600) is one of the most common inborn errors of metabolism (IEM) with an incidence of 1:10000 in the European population. PKU is caused by autosomal recessive mutations in phenylalanine hydroxylase (PAH) and manifests with elevation of phenylalanine (Phe) in plasma and urine. Untreated PKU manifests with intellectual disability including seizures, microcephaly and behavioral abnormalities. Early treatment and good compliance result in a normal intellectual outcome in many but not in all patients. This study examined plasma metabolites in patients with PKU (n = 27), hyperphenylalaninemia (HPA, n = 1) and healthy controls (n = 32) by LC- MS/MS. We hypothesized that PKU patients would exhibit a distinct "submetabolome" compared to that of healthy controls. We further hypothesized that the submetabolome of PKU patients with good metabolic control would resemble that of healthy controls. Results from this study show: (i) Distinct clustering of healthy controls and PKU patients based on polar metabolite profiling, (ii) Increased and decreased concentrations of metabolites within and afar from the Phe pathway in treated patients, and (iii) A specific PKU-submetabolome independently of metabolic control assessed by Phe in plasma. We examined the relationship between PKU metabolic control and extended metabolite profiles in plasma. The PKU submetabolome characterized in this study represents the combined effects of dietary adherence, adjustments in metabolic pathways to compensate for defective Phe processing, as well as metabolic derangements that could not be corrected with dietary management even in patients classified as having good metabolic control. New therapeutic targets may be uncovered to approximate the PKU submetabolome to that of healthy controls and prevent long-term organ damage.

Genomic newborn screening: Are we entering a new era of screening?

Population newborn screening (NBS) for phenylketonuria began in the United States in 1963. In the 1990s electrospray ionization mass spectrometry permitted an array of pathognomonic metabolites to be identified simultaneously, enabling up to 60 disorders to be recognized with a single test. In response, differing approaches to the assessment of the harms and benefits of screening have resulted in variable screening panels worldwide. Thirty years on and another screening revolution has emerged with the potential for first line genomic testing extending the range of screening conditions recognized after birth to many hundreds. At the annual SSIEM conference in 2022 in Freiburg, Germany, an interactive plenary discussion on genomic screening strategies and their challenges and opportunities was conducted. The Genomics England Research project proposes the use of Whole Genome Sequencing to offer extended NBS to 100 000 babies for defined conditions with a clear benefit for the child. The European Organization for Rare Diseases seeks to include "actionable" conditions considering also other types of benefits. Hopkins Van Mil, a private UK research institute, determined the views of citizens and revealed as a precondition that families are provided with adequate information, qualified support, and that autonomy and data are protected. From an ethical standpoint, the benefits ascribed to screening and early treatment need to be considered in relation to asymptomatic, phenotypically mild or late-onset presentations, where presymptomatic treatment may not be required. The different perspectives and arguments demonstrate the unique burden of responsibility on those proposing new and far-reaching developments in NBS programs and the need to carefully consider both harms and benefits.

Isovaleric aciduria identified by newborn screening: Strategies to predict disease severity and stratify treatment.

Newborn screening (NBS) allows early identification of individuals with rare disease, such as isovaleric aciduria (IVA). Reliable early prediction of disease severity of positively screened individuals with IVA is needed to guide therapeutic decision, prevent life-threatening neonatal disease manifestation in classic IVA and over-medicalization in attenuated IVA that may remain asymptomatic. We analyzed 84 individuals (median age at last study visit 8.5 years) with confirmed IVA identified by NBS between 1998 and 2018 who participated in the national, observational, multicenter study. Screening results, additional metabolic parameters, genotypes, and clinical phenotypic data were included. Individuals with metabolic decompensation showed a higher median isovalerylcarnitine (C5) concentration in the first NBS sample (10.6 vs. 2.7 µmol/L; p < 0.0001) and initial urinary isovalerylglycine concentration (1750 vs. 180 mmol/mol creatinine; p = 0.0003) than those who remained asymptomatic. C5 was in trend inversely correlated with full IQ (R = -0.255; slope = -0.869; p = 0.0870) and was lower for the "attenuated" variants compared to classic genotypes [median (IQR; range): 2.6 µmol/L (2.1-4.0; 0.7-6.4) versus 10.3 µmol/L (7.4-13.1; 4.3-21.7); N = 73]. In-silico prediction scores (M-CAP, MetaSVM, and MetaLR) correlated highly with isovalerylglycine and ratios of C5 to free carnitine and acetylcarnitine, but not sufficiently with clinical endpoints. The results of the first NBS sample and biochemical confirmatory testing are reliable early predictors of the clinical course of IVA, facilitating case definition (attenuated versus classic IVA). Prediction of attenuated IVA is supported by the genotype. On this basis, a reasonable algorithm has been established for neonates with a positive NBS result for IVA, with the aim of providing the necessary treatment immediately, but whenever possible, adjusting the treatment to the individual severity of the disease.

Elevated holo-transcobalamin in Gaucher disease type II: A case report.

Gaucher disease (GD), one of the most common lysosomal disorders, is caused by deficiency of ß-glucocerebrosidase. Based on the presence and severity of neurological complications, GD is classified into types I, II (the most severe form), and III. Abnormalities in systemic markers of vitamin B12 (B12 ) metabolism have been reported in GD type I patients, suggesting a higher prevalence of B12 deficiency in these patients. A 2-month-old male with GD type II was admitted to the hospital presenting jaundice, hepatosplenomegaly, and ichthyosis. At admission, cholestasis and ascites, abnormal liver function enzymes, prolonged prothrombin time, and high levels of B12 were confirmed. Analysis of biomarkers of B12 status revealed elevated B12 and holo-transcobalamin (holo-TC) levels. The B12 profile found in our patient is the opposite to what is described for GD type I patients. Holo-TC may increase in inflammatory states or due to liver diseases. In GD, the accumulation of glucocerebroside may be a trigger that initiates a systemic inflammatory reaction, characterized by macrophage activation. We suggest higher levels of holo-TC could be associated with a more severe (neuronopathic) GD, and be a biomarker of GD type II.

Mitochondrial damage in renal epithelial cells is potentiated by protein exposure in propionic aciduria.

Propionic aciduria (PA) is caused by deficiency of the mitochondrial enzyme propionyl-CoA carboxylase (PCC). Due to inefficient propionate catabolism patients are endangered by life-threatening ketoacidotic crisis. Protein and amino acid restriction are major therapeutic pillars. However, long-term complications like neurological deterioration and cardiac abnormalities cannot be prevented. Chronic kidney disease (CKD), which is a well-known characteristic of methylmalonic aciduria two enzymatic steps downstream from PCC, has been recognized as a novel late-onset complication in PA. The pathophysiology of CKD in PA is unclear. We investigated mitochondrial structure and metabolism in human renal tubular cells of healthy controls and PA patients. The cells were exposed to either standard cell culture conditions (NT), high protein (HP) or high concentrations of isoleucine and valine (I/V). Mitochondrial morphology changed to condensed, fractured morphology in PA cells irrespective of the cell culture medium. HP and I/V exposure, however, potentiated oxidative stress in PA cells. Mitochondrial mass was enriched in PA cells, and further increased by HP and I/V exposure suggesting a need for compensation. Alterations in the tricarboxylic acid cycle intermediates and accumulation of medium- and long-chain acylcarnitines pointed to altered mitochondrial energy metabolism. Mitophagy was silenced while autophagy as cellular defense mechanisms was highly active in PA cells. The data demonstrate that PA is associated with renal mitochondrial damage which is aggravated by protein and I/V load. Preservation of mitochondrial energy homeostasis in renal cells may be a potential future therapeutic target.

The spectrum of peripheral neuropathy in disorders of the mitochondrial trifunctional protein.

Peripheral neuropathy is a known irreversible long-term complication of long-chain 3-hydroxyacyl-CoA dehydrogenase deficiency (LCHADD) and mitochondrial trifunctional protein deficiency (MTPD), two inherited disorders of mitochondrial long-chain fatty acid oxidation. The underlying pathophysiology of neuropathy is still not fully understood. We report electrophysiological studies and neurological findings in a series of 8 LCHAD-deficient and 11 MTP-deficient patients. The median age at time of the study was 8.0 years (0.5-25 years). The overall prevalence of neuropathy was 58% with neuropathic symptoms being slightly more common in MTPD compared to LCHADD (70% vs 50%, respectively). Onset of neuropathy was significantly earlier in MTPD patients compared to LCHADD patients (median age at onset 4.7 vs 15.3 years, respectively, P = .047). In four patients, isolated peripheral neuropathy was the first and only presenting symptom, and in all four the diagnosis was missed by newborn screening. About half of the patients (45.5%) had a sensorimotor neuropathy, while 27.3% showed a pure motor form and another 27.3% an isolated sensory form. Despite early diagnosis by newborn screening and early initiation of therapy, peripheral neuropathy cannot be prevented in all patients with LCHADD/MTPD and has severe impact on the life of affected patients. Electrophysiology classifies LCHADD/MTPD neuropathy as axonal with secondary demyelination. A novel observation is that in patients with acute, fulminant onset of neuropathy, symptoms can be partly reversible. Further studies are needed to elucidate the underlying pathophysiology of axonal damage and possible therapeutic targets.

Defective lysosomal storage in Fabry disease modifies mitochondrial structure, metabolism and turnover in renal epithelial cells.

Fabry disease (FD) is an X-linked lysosomal storage disorder. Deficiency of the lysosomal enzyme alpha-galactosidase (GLA) leads to accumulation of potentially toxic globotriaosylceramide (Gb3) on a multisystem level. Cardiac and cerebrovascular abnormalities as well as progressive renal failure are severe, life-threatening long-term complications. The complete pathophysiology of chronic kidney disease (CKD) in FD and the role of tubular involvement for its progression are unclear. We established human renal tubular epithelial cell lines from the urine of male FD patients and male controls. The renal tubular system is rich in mitochondria and involved in transport processes at high-energy costs. Our studies revealed fragmented mitochondria with disrupted cristae structure in FD patient cells. Oxidative stress levels were elevated and oxidative phosphorylation was upregulated in FD pointing at enhanced energetic needs. Mitochondrial homeostasis and energy metabolism revealed major changes as evidenced by differences in mitochondrial number, energy production and fuel consumption. The changes were accompanied by activation of the autophagy machinery in FD. Sirtuin1, an important sensor of (renal) metabolic stress and modifier of different defense pathways, was highly expressed in FD. Our data show that lysosomal FD impairs mitochondrial function and results in severe disturbance of mitochondrial energy metabolism in renal cells. This insight on a tissue-specific level points to new therapeutic targets which might enhance treatment efficacy.

Genotype and residual enzyme activity in medium-chain acyl-CoA dehydrogenase (MCAD) deficiency: Are predictions possible?

Medium-chain acyl-CoA dehydrogenase deficiency (MCADD) is the most common defect of mitochondrial ß-oxidation. Confirmation diagnostics after newborn screening (NBS) can be performed either by enzyme testing and/or by sequencing of the ACADM gene. Here, we report the results from enzyme testing in lymphocytes with gene variants from molecular analysis of the ACADM gene and with the initial acylcarnitine concentrations in the NBS sample. From April 2013 to August 2019, in 388 individuals with characteristic acylcarnitine profiles suggestive of MCADD the octanoyl-CoA-oxidation was measured in lymphocytes. In those individuals with residual activities <50%, molecular genetic analysis of the ACADM gene was performed. In 50% of the samples (195/388), MCADD with a residual activity ranging from 0% to 30% was confirmed. Forty-five percent of the samples (172/388) showed a residual activity >35% excluding MCADD. In the remaining 21 individuals, MCAD residual activity ranged from 30% to 35%. The latter group comprised both heterozygous carriers and individuals carrying two gene variants on different alleles. Twenty new variants could be identified and functionally classified based on their effect on enzyme function. C6 and C8 acylcarnitine species in NBS correlated with MCAD activity and disease severity. MCADD was only confirmed in half of the cases referred suggesting a higher false positive rate than expected. Measurement of the enzyme function in lymphocytes allowed fast confirmation diagnostics and clear determination of the pathogenicity of new gene variants. There is a clear correlation between genotype and enzyme function underlining the reproducibility of the functional measurement in vitro.

Newborn screening and disease variants predict neurological outcome in isovaleric aciduria.

Isovaleric aciduria (IVA), a metabolic disease with severe (classic IVA) or attenuated phenotype (mild IVA), is included in newborn screening (NBS) programs worldwide. The long-term clinical benefit of screened individuals, however, is still rarely investigated. A national, prospective, observational, multi-center study of individuals with confirmed IVA identified by NBS between 1998 and 2018 was conducted. Long-term clinical outcomes of 94 individuals with IVA were evaluated, representing 73.4% (for classic IVA: 92.3%) of the German NBS cohort. In classic IVA (N = 24), NBS prevented untimely death except in one individual with lethal neonatal sepsis (3.8%) but did not completely prevent single (N = 10) or recurrent (N = 7) metabolic decompensations, 13 of them occurring already neonatally. IQ (mean ± SD, 90.7 ± 10.1) was mostly normal but below the reference population (P = .0022) and was even lower in individuals with severe neonatal decompensations (IQ 78.8 ± 7.1) compared to those without crises (IQ 94.7 ± 7.5; P = .01). Similar results were obtained for school placement. In contrast, individuals with mild IVA had excellent neurocognitive outcomes (IQ 105.5 ± 15.8; normal school placement) and a benign disease course (no metabolic decompensation, normal hospitalization rate), which did not appear to be impacted by metabolic maintenance therapy. In conclusion, NBS reduces mortality in classic IVA, but does not reliably protect against severe neonatal metabolic decompensations, crucial for favorable neurocognitive outcome. In contrast, individuals with mild IVA had excellent clinical outcomes regardless of metabolic maintenance therapy, questioning their benefit from NBS. Harmonized stratified therapeutic concepts are urgently needed.

Glycogen storage disease type I patients with hyperlipidemia have no signs of early vascular dysfunction and premature atherosclerosis.

BACKGROUND AND AIMS: Glycogen storage disease type I (GSD I) is associated with hyperlipidemia, a known risk factor for premature atherosclerosis. Few studies have addressed endothelial dysfunction in patients with GSD I, and these studies yielded controversial results. METHODS AND RESULTS: We investigated vascular dysfunction in a cohort of 32 patients with GSD I (26 GSD Ia, 6 GSD Ib, mean age 20.7 (4.8-47.5) years) compared to 32 age-, gender-, and BMI-matched healthy controls using non-invasive techniques such as quantification of carotid intima media thickness, retinal vessel analysis and 24 h-blood pressure measurements. In addition, early biomarkers of inflammatory and oxidative endothelial stress were assessed in blood. Although GSD I patients had a clearly proatherogenic lipid profile, increased oxidative stress, higher levels of high sensitivity C-reactive protein and increased lipoprotein associated phospholipase A2 activity, functional and structural parameters including carotid intima media thickness and retinal vessel diameters did not indicate premature atherosclerosis in this patient cohort. Blood pressure values and pulse wave velocity were comparable in patients and healthy controls, while central blood pressure and augmentation index were higher in GSD patients. CONCLUSION: Our data suggest that GSD I is not associated with early vascular dysfunction up to the age of at least 20 years. Further studies are needed to elucidate the possibly protective mechanisms that prevent early atherosclerosis is GSD I. Longer follow-up studies are required to assess the long-term risk of vascular disease with increased oxidative stress being present in GSD I patients.

Assessment of cellular cobalamin metabolism in Gaucher disease.

BACKGROUND: Gaucher disease (GD) is a lysosomal disorder caused by biallelic pathogenic mutations in the GBA1 gene that encodes beta-glucosidase (GCase), and more rarely, by a deficiency in the GCase activator, saposin C. Clinically, GD manifests with heterogeneous multiorgan involvement mainly affecting hematological, hepatic and neurological axes. This disorder is divided into three types, based on the absence (type I) or presence and severity (types II and III) of involvement of the central nervous system. At the cellular level, deficiency of GBA1 disturbs lysosomal storage with buildup of glucocerebroside. The consequences of disturbed lysosomal metabolism on biochemical pathways that require lysosomal processing are unknown. Abnormal systemic markers of cobalamin (Cbl, B12) metabolism have been reported in patients with GD, suggesting impairments in lysosomal handling of Cbl or in its downstream utilization events. METHODS: Cultured skin fibroblasts from control humans (n = 3), from patients with GD types I (n = 1), II (n = 1) and III (n = 1) and an asymptomatic carrier of GD were examined for their GCase enzymatic activity and lysosomal compartment intactness. Control human and GD fibroblasts were cultured in growth medium with and without 500 nM hydroxocobalamin supplementation. Cellular cobalamin status was examined via determination of metabolomic markers in cell lysate (intracellular) and conditioned culture medium (extracellular). The presence of transcobalamin (TC) in whole cell lysates was examined by Western blot. RESULTS: Cultured skin fibroblasts from GD patients exhibited reduced GCase activity compared to healthy individuals and an asymptomatic carrier of GD, demonstrating a preserved disease phenotype in this cell type. The concentrations of total homocysteine (tHcy), methylmalonic acid (MMA), cysteine (Cys) and methionine (Met) in GD cells were comparable to control levels, except in one patient with GD III. The response of these metabolomic markers to supplementation with hydroxocobalamin (HOCbl) yielded variable results. The content of transcobalamin in whole cell lysates was comparable in control human and GD patients. CONCLUSIONS: Our results indicate that cobalamin transport and cellular processing pathways are overall protected from lysosomal storage damage in GD fibroblasts. Extending these studies to hepatocytes, macrophages and plasma will shed light on cell- and compartment-specific vitamin B12 metabolism in Gaucher disease.

Implementation of a fast method for the measurement of carnitine palmitoyltransferase 2 activity in lymphocytes by tandem mass spectrometry as confirmation for newborn screening.

Carnitine palmitoyltransferase II (CPT2) is a rare autosomal recessive inherited disorder affecting mitochondrial ß-oxidation. Confirmation diagnostics are mostly based on molecular sequencing of the CPT2 gene, especially to distinguish CPT2 and carnitine:aclycarnitine translocase deficiencies, which present with identical acylcarnitine profiles on newborn screening (NBS). In the past, different enzyme tests in muscle biopsies have been developed in order to study the functional effect in one of the main target organs. In this study, we implemented a method for measurement of CPT2 enzyme activity in human lymphocytes with detection of the reaction products via liquid chromatography mass spectrometry to enable the simultaneous evaluation of the functional impairment and the clear diagnosis of the disease. CPT2 activity was measured in samples collected from CPT2 patients (n = 11), heterozygous carriers (n = 6), and healthy individuals (n = 52). Seven patients out of 11 were homozygous for the common mutation c.338T>C and showed a residual activity with median values of 19.2 ± 3.7% of healthy controls. Heterozygous carriers showed a residual activity in the range of 42% to 75%. Four individuals carrying the heterozygous mutation c.338T>C showed a 2-fold higher residual activity as compared to homozygous individuals. Our optimized method for the measurement of CPT2 activity is able to clearly discriminate between patients and healthy individuals and offers the possibility to determine CPT2 activity in human lymphocytes avoiding the need of an invasive muscle biopsy. This method can be successfully used for confirmation diagnosis in case of positive NBS and would markedly reduce the time to define diagnosis.

Genome-Wide Association Studies of Metabolites in Patients with CKD Identify Multiple Loci and Illuminate Tubular Transport Mechanisms.

Background The kidneys have a central role in the generation, turnover, transport, and excretion of metabolites, and these functions can be altered in CKD. Genetic studies of metabolite concentrations can identify proteins performing these functions.Methods We conducted genome-wide association studies and aggregate rare variant tests of the concentrations of 139 serum metabolites and 41 urine metabolites, as well as their pairwise ratios and fractional excretions in up to 1168 patients with CKD.Results After correction for multiple testing, genome-wide significant associations were detected for 25 serum metabolites, two urine metabolites, and 259 serum and 14 urinary metabolite ratios. These included associations already known from population-based studies. Additional findings included an association for the uremic toxin putrescine and variants upstream of an enzyme catalyzing the oxidative deamination of polyamines (AOC1, P-min=2.4×10-12), a relatively high carrier frequency (2%) for rare deleterious missense variants in ACADM that are collectively associated with serum ratios of medium-chain acylcarnitines (P-burden=6.6×10-16), and associations of a common variant in SLC7A9 with several ratios of lysine to neutral amino acids in urine, including the lysine/glutamine ratio (P=2.2×10-23). The associations of this SLC7A9 variant with ratios of lysine to specific neutral amino acids were much stronger than the association with lysine concentration alone. This finding is consistent with SLC7A9 functioning as an exchanger of urinary cationic amino acids against specific intracellular neutral amino acids at the apical membrane of proximal tubular cells.Conclusions Metabolomic indices of specific kidney functions in genetic studies may provide insight into human renal physiology.

The diagnostic challenge in very-long chain acyl-CoA dehydrogenase deficiency (VLCADD).

Very long-chain acyl-CoA dehydrogenase deficiency (VLCADD) is the most common defect of mitochondrial ß-oxidation of long-chain fatty acids. However, the unambiguous diagnosis of true VLCADD patients may be challenging, and a high rate of false positive individuals identified by newborn screening undergo confirmation diagnostics. In this study, we show the outcome of enzyme testing in lymphocytes as a confirmatory tool in newborns identified by screening, and the correlation with molecular sequencing of the ACADVL gene. From April 2013 to March 2017, in 403 individuals with characteristic acylcarnitine profiles indicative of VLCADD, palmitoyl-CoA oxidation was measured followed by molecular genetic analysis in most of the patients with residual activity (RA) <50%. In almost 50% of the samples (209/403) the RA was >50%, one-third of the individuals (125/403) displayed a RA of 30-50% and 69/403 individuals showed a residual activity of 0-30%. Sequencing of the ACADVL gene revealed that all individuals with activities below 24% were true VLCADD patients, individuals with residual activities between 24 and 27% carried either one or two mutations. Twenty new mutations could be identified and functionally classified based on their effect on enzyme function. Finally, we observed an up-regulation of MCAD-activity in many patients. However, this did not correlate with the degree of VLCAD RA. Although the likely clinical phenotype cannot be fully foreseen by genetic and functional tests as it depends on many factors, our data demonstrate the strength of this functional enzyme test in lymphocytes as a quick and reliable method for confirmation diagnostics of VLCADD.

Successful pregnancy in maple syrup urine disease: a case report and review of the literature.

BACKGROUND: Maple syrup urine disease (MSUD) is an autosomal recessive disorder of branched-chain amino acid metabolism. Patients with MSUD are at risk of life-threatening metabolic decompensations with ketoacidosis and encephalopathy. These episodes are often triggered by physiological stress. Only few cases of pregnancies in MSUD mothers have been reported so far. CASE PRESENTATION: We present the favorable outcome of a pregnancy in a woman with classical MSUD. She presented in the metabolic outpatient clinic in week 7 of gestation. Branched-chain amino acid concentrations were measured at least weekly to adjust dietary leucine intake. Despite excellent compliance, leucine concentrations frequently exceeded the target value of < 300 µmol/L during the first trimester. From the second trimester until delivery, protein and leucine intake increased continuously to about threefold compared to pre-pregnancy values. To maximize patient safety during delivery and the postpartum period, a detailed plan including peripartal infusion therapy, dietary recommendations and monitoring parameters was developed. Primary Caesarean section was performed in week 38 of gestation, and the patient gave birth to a healthy girl. Lactation was successfully implemented. Leucine levels were maintained within the target range throughout the complete postpartum period. In addition to our case, we give an overview about all cases of pregnancies in MSUD mothers published so far. CONCLUSIONS: Management of pregnancy, delivery, postpartum period and lactation may be challenging in patients with MSUD. Careful monitoring and interdisciplinary collaboration is essential to minimize the risk of metabolic crisis, especially after delivery.

Triheptanoin: long-term effects in the very long-chain acyl-CoA dehydrogenase-deficient mouse.

A rather new approach in the treatment of long-chain fatty acid oxidation disorders is represented by triheptanoin, a triglyceride with three medium-odd-chain heptanoic acids (C7), due to its anaplerotic potential. We here investigate the effects of a 1-year triheptanoin-based diet on the clinical phenotype of very long-chain-acyl-CoA-dehydrogenase-deficient (VLCAD-/-) mice. The cardiac function was assessed in VLCAD-/- mice by in vivo MRI. Metabolic adaptations were identified by the expression of genes regulating energy metabolism and anaplerotic processes using real-time PCR, and the results were correlated with the measurement of the glycolytic enzymes pyruvate dehydrogenase and pyruvate kinase. Finally, the intrahepatic lipid accumulation and oxidative stress in response to the long-term triheptanoin diet were assessed. Triheptanoin was not able to prevent the development of systolic dysfunction in VLCAD-/- mice despite an upregulation of cardiac glucose oxidation. Strikingly, the anaplerotic effects of triheptanoin were restricted to the liver. Despite this, the hepatic lipic content was increased upon triheptanoin supplementation. Our data demonstrate that the concept of anaplerosis does not apply to all tissues equally.

Sexual dimorphism of lipid metabolism in very long-chain acyl-CoA dehydrogenase deficient (VLCAD-/-) mice in response to medium-chain triglycerides (MCT).

Medium-chain triglycerides (MCT) are widely applied in the treatment of long-chain fatty acid oxidation disorders. Previously it was shown that long-term MCT supplementation strongly affects lipid metabolism in mice. We here investigate sex-specific effects in mice with very-long-chain-acyl-CoA dehydrogenase (VLCAD) deficiency in response to a long-term MCT modified diet. We quantified blood lipids, acylcarnitines, glucose, insulin and free fatty acids, as well as tissue triglycerides in the liver and skeletal muscle under a control and an MCT diet over 1 year. In addition, visceral and hepatic fat content and muscular intramyocellular lipids (IMCL) were assessed by in vivo(1)H magnetic resonance spectroscopy (MRS) techniques. The long-term application of an MCT diet induced a marked alteration of glucose homeostasis. However, only VLCAD-/- female mice developed a severe metabolic syndrome characterized by marked insulin resistance, dyslipidemia, severe hepatic and visceral steatosis, whereas VLCAD-/- males seemed to be protected and only presented with milder insulin resistance. Moreover, the highly saturated MCT diet is associated with a decreased hepatic stearoyl-CoA desaturase 1 (SCD1) activity in females aggravating the harmful effects of a saturated MCT diet. Long-term MCT supplementation deeply affects lipid metabolism in a sexual dimorphic manner resulting in a severe metabolic syndrome only in female mice. These findings are striking since the first signs of insulin resistance already occur in female VLCAD-/- mice during their reproductive period. How these metabolic adaptations are finally regulated needs to be determined. More important, the relevance of these findings for humans under these dietary modifications needs to be investigated.

Clinical pattern, mutations and in vitro residual activity in 33 patients with severe 5, 10 methylenetetrahydrofolate reductase (MTHFR) deficiency.

BACKGROUND: Severe methylenetetrahydrofolate reductase (MTHFR) deficiency is a rare inborn defect disturbing the remethylation of homocysteine to methionine (<200 reported cases). This retrospective study evaluates clinical, biochemical genetic and in vitro enzymatic data in a cohort of 33 patients. METHODS: Clinical, biochemical and treatment data was obtained from physicians by using a questionnaire. MTHFR activity was measured in primary fibroblasts; genomic DNA was extracted from cultured fibroblasts. RESULTS: Thirty-three patients (mean age at follow-up 11.4 years; four deceased; median age at first presentation 5 weeks; 17 females) were included. Patients with very low (<1.5%) mean control values of enzyme activity (n = 14) presented earlier and with a pattern of feeding problems, encephalopathy, muscular hypotonia, neurocognitive impairment, apnoea, hydrocephalus, microcephaly and epilepsy. Patients with higher (>1.7-34.8%) residual enzyme activity had mainly psychiatric symptoms, mental retardation, myelopathy, ataxia and spasticity. Treatment with various combinations of betaine, methionine, folate and cobalamin improved the biochemical and clinical phenotype. During the disease course, patients with very low enzyme activity showed a progression of feeding problems, neurological symptoms, mental retardation, and psychiatric disease while in patients with higher residual enzyme activity, myelopathy, ataxia and spasticity increased. All other symptoms remained stable or improved in both groups upon treatment as did brain imaging in some cases. No clear genotype-phenotype correlation was obvious. DISCUSSION: MTHFR deficiency is a severe disease primarily affecting the central nervous system. Age at presentation and clinical pattern are correlated with residual enzyme activity. Treatment alleviates biochemical abnormalities and clinical symptoms partially.

Development and pathomechanisms of cardiomyopathy in very long-chain acyl-CoA dehydrogenase deficient (VLCAD(-/-)) mice.

Hypertrophic cardiomyopathy is a typical manifestation of very long-chain acyl-CoA dehydrogenase deficiency (VLCADD), the most common long-chain ß-oxidation defects in humans; however in some patients cardiac function is fully compensated. Cardiomyopathy may also be reversed by supplementation of medium-chain triglycerides (MCT). We here characterize cardiac function of VLCAD-deficient (VLCAD(-/-)) mice over one year. Furthermore, we investigate the long-term effect of a continuous MCT diet on the cardiac phenotype. We assessed cardiac morphology and function in VLCAD(-/-) mice by in vivo MRI. Cardiac energetics were measured by (31)P-MRS and myocardial glucose uptake was quantified by positron-emission-tomography (PET). Metabolic adaptations were identified by the expression of genes regulating glucose and lipid metabolism using real-time-PCR. VLCAD(-/-) mice showed a progressive decrease in heart function over 12 months accompanied by a reduced phosphocreatine-to-ATP-ratio indicative of chronic energy deficiency. Long-term MCT supplementation aggravated the cardiac phenotype into dilated cardiomyopathy with features similar to diabetic heart disease. Cardiac energy production and function in mice with a ß-oxidation defect cannot be maintained with age. Compensatory mechanisms are insufficient to preserve the cardiac energy state over time. However, energy deficiency by impaired ß-oxidation and long-term MCT induce cardiomyopathy by different mechanisms. Cardiac MRI and MRS may be excellent tools to assess minor changes in cardiac function and energetics in patients with ß-oxidation defects for preventive therapy.