An autosomal dominant neurological disorder caused by de novo variants in FAR1 resulting in uncontrolled synthesis of ether lipids.

PURPOSE: In this study we investigate the disease etiology in 12 patients with de novo variants in FAR1 all resulting in an amino acid change at position 480 (p.Arg480Cys/His/Leu). METHODS: Following next-generation sequencing and clinical phenotyping, functional characterization was performed in patients' fibroblasts using FAR1 enzyme analysis, FAR1 immunoblotting/immunofluorescence, and lipidomics. RESULTS: All patients had spastic paraparesis and bilateral congenital/juvenile cataracts, in most combined with speech and gross motor developmental delay and truncal hypotonia. FAR1 deficiency caused by biallelic variants results in defective ether lipid synthesis and plasmalogen deficiency. In contrast, patients' fibroblasts with the de novo FAR1 variants showed elevated plasmalogen levels. Further functional studies in fibroblasts showed that these variants cause a disruption of the plasmalogen-dependent feedback regulation of FAR1 protein levels leading to uncontrolled ether lipid production. CONCLUSION: Heterozygous de novo variants affecting the Arg480 residue of FAR1 lead to an autosomal dominant disorder with a different disease mechanism than that of recessive FAR1 deficiency and a diametrically opposed biochemical phenotype. Our findings show that for patients with spastic paraparesis and bilateral cataracts, FAR1 should be considered as a candidate gene and added to gene panels for hereditary spastic paraplegia, cerebral palsy, and juvenile cataracts.

Fatty acid oxidation flux predicts the clinical severity of VLCAD deficiency.

PURPOSE: Very-long-chain acyl-CoA dehydrogenase (VLCAD) deficiency (VLCADD) is an inherited disorder of mitochondrial long-chain fatty acid ß-oxidation (LC-FAO) and is included in many newborn screening (NBS) programs worldwide. Patients may present with hypoketotic hypoglycemia, cardiomyopathy, and/or myopathy, but clinical severity varies widely and the clinical outcome is unpredictable. We investigated predictive markers that may determine clinical severity. METHODS: We developed a clinical severity score (CSS), which was determined for 13 Dutch patients with VLCADD, all of whom were diagnosed before the introduction of VLCADD in NBS to prevent bias from early diagnosis. In cultured skin fibroblasts from these patients, we measured LC-FAO flux (the rate of oleate oxidation), VLCAD activity, and acylcarnitine profiles following palmitate loading. RESULTS: The strongest correlation (r = 0.93; P < 0.0001) was observed between LC-FAO flux and the CSS. VLCAD activity measurement and the C14/C16-to-acylcarnitine ratio correlated much less. A median LC-FAO flux of 6% of control values (range 5.6-6.8%) was associated with cardiomyopathy (P < 0.01), and 32.4% (range 5.6-50.5%) was associated with myopathy (P < 0.05). CONCLUSION: Our results demonstrate a very strong correlation between LC-FAO flux in fibroblasts and the clinical severity of VLCADD. LC-FAO flux measurements may thus predict whether patients are likely to develop symptoms.

Rosuvastatin lowers coenzyme Q10 levels, but not mitochondrial adenosine triphosphate synthesis, in children with familial hypercholesterolemia.

OBJECTIVE: To investigate whether statin therapy affects coenzyme Q10 (CoQ10) status in children with heterozygous familial hypercholesterolemia (FH). STUDY DESIGN: Samples were obtained at baseline (treatment naïve) and after dose titration with rosuvastatin, aiming for a low-density lipoprotein cholesterol level of 110 mg/dL. Twenty-nine patients were treated with 5, 10, or 20 mg of rosuvastatin for a mean period of 29 weeks. RESULTS: We found a significant (32%) decrease in peripheral blood mononuclear cell (PBMC) CoQ10 level (P = .02), but no change in PBMC adenosine triphosphate synthesis (P = .60). Uncorrected plasma CoQ10 values were decreased significantly, by 45% (P < .01). In contrast, ratios of plasma CoQ10/total cholesterol and CoQ10/low-density lipoprotein cholesterol remained equal during treatment. CONCLUSIONS: In children with FH, rosuvastatin causes a significant decrease in cellular PBMC CoQ10 status but does not affect mitochondrial adenosine triphosphate synthesis in children with FH. Further studies should address whether (rare) side effects of statin therapy could be explained by a deterioration in CoQ10 status.

Valproic acid metabolites inhibit dihydrolipoyl dehydrogenase activity leading to impaired 2-oxoglutarate-driven oxidative phosphorylation.

The effect of the antiepileptic drug valproic acid (VPA) on mitochondrial oxidative phosphorylation (OXPHOS) was investigated in vitro. Two experimental approaches were used, in the presence of selected respiratory-chain substrates: (1) formation of ATP in digitonin permeabilized rat hepatocytes and (2) measurement of the rate of oxygen consumption by polarography in rat liver mitochondria. VPA (0.1-1.0 mM) was found to inhibit oxygen consumption and ATP synthesis under state 3 conditions with glutamate and 2-oxoglutarate as respiratory substrates. No inhibitory effect on OXPHOS was observed when succinate (plus rotenone) was used as substrate. We tested the hypothesis that dihydrolipoyl dehydrogenase (DLDH) might be a direct target of VPA, especially its acyl-CoA intermediates. Valproyl-CoA (0.5-1.0 mM) and valproyl-dephosphoCoA (0.5-1.0 mM) both inhibited the DLDH activity, acting apparently by different mechanisms. The decreased activity of DLDH induced by VPA metabolites may, at least in part, account for the impaired rate of oxygen consumption and ATP synthesis in mitochondria if 2-oxoglutarate or glutamate were used as respiratory substrates, thus limiting the flux of these substrates through the citric acid cycle.

Fatty acid oxidation in the human fetus: implications for fetal and adult disease.

Studies in the last few years have shown a remarkably high activity of fatty acid oxidation (FAO) enzymes in human placenta. We have recently shown mRNA expression as well as enzymatic activity of long-chain FAO enzymes in the human embryo and fetus. In this study we show activity of the FAO enzymes carnitine palmitoyltranferase 1, medium-chain acyl-CoA dehydrogenase and short-chain hydroxyacyl-CoA dehydrogenase in embryonic and fetal tissues. In addition, we show the presence of different acylcarnitines in fetal liver and kidney, which substantiates the notion that the mitochondrial FAO enzymes are not only present in human fetal tissues but also metabolically active. In a glucose-rich environment FAO might be necessary for additional ATP production from fatty acids, but also for the breakdown of fatty acids that are products of the turnover of membranes in the growing fetus. The importance of FAO in the human embryo and fetus is further stressed by the fact that a higher frequency of prematurity, intrauterine growth retardation, fetal morbidity and intrauterine death is noted in long-chain FAO defects. Furthermore, in animal studies, gestational loss during early embryonic development has been observed as a consequence of disturbed FAO. Finally, there are indications that regulation of activity of FAO during fetal development might not only be important for fetal life but may also have implications for health and disease in adulthood.

Spastic diplegia and periventricular white matter abnormalities in 2-methyl-3-hydroxybutyryl-CoA dehydrogenase deficiency, a defect of isoleucine metabolism: differential diagnosis with hypoxic-ischemic brain diseases.

A 19-month-old boy with 2-methyl-3-hydroxybutyryl-CoA dehydrogenase (MHBD) deficiency, a defect of isoleucine degradation, had cognitive and motor development delay, spastic diplegia, dysmorphism, and occipital periventricular white matter lesions on MRI scan of the brain. The urinary accumulation of the isoleucine metabolites 2-methyl-3-hydroxybutyrate and tiglylglycine was only moderate under basal conditions. These abnormalities became more pronounced after a 100mg/kg oral isoleucine challenge. Enzyme studies showed a markedly decreased activity of MHBD in fibroblasts and lymphocytes. Sequence analysis of the involved X-chromosome gene (HADH2), revealed the presence of 364C -->G mutation in the patient. His mother was heterozygous for the 364C-->G mutation, whereas the mutation was not found in the other members of the family (father, brother, and sister). This report indicates that an enzyme defect in the metabolism of branched-chain fatty acid oxidation and isoleucine may present features resembling sequelae of neonatal hypoxic-ischemic brain injury. All patients with MHBD deficiency identified so far are characterized by a neurologic phenotype rather than ketoacidotic attacks, unlike patients with the related isoleucine defect beta-ketothiolase deficiency.