Clinical and biochemical characterization of four patients with mutations in ECHS1

Abstract

BackgroundShort-chain enoyl-CoA hydratase (SCEH, encoded by ECHS1) catalyzes hydration of 2-trans-enoyl-CoAs to 3(S)-hydroxy-acyl-CoAs. SCEH has a broad substrate specificity and is believed to play an important role in mitochondrial fatty acid oxidation and in the metabolism of branched-chain amino acids. Recently, the first patients with SCEH deficiency have been reported revealing only a defect in valine catabolism. We investigated the role of SCEH in fatty acid and branched-chain amino acid metabolism in four newly identified patients. In addition, because of the Leigh-like presentation, we studied enzymes involved in bioenergetics.MethodsMetabolite, enzymatic, protein and genetic analyses were performed in four patients, including two siblings. Palmitate loading studies in fibroblasts were performed to study mitochondrial β-oxidation. In addition, enoyl-CoA hydratase activity was measured with crotonyl-CoA, methacrylyl-CoA, tiglyl-CoA and 3-methylcrotonyl-CoA both in fibroblasts and liver to further study the role of SCEH in different metabolic pathways. Analyses of pyruvate dehydrogenase and respiratory chain complexes were performed in multiple tissues of two patients.ResultsAll patients were either homozygous or compound heterozygous for mutations in the ECHS1 gene, had markedly reduced SCEH enzymatic activity and protein level in fibroblasts. All patients presented with lactic acidosis. The first two patients presented with vacuolating leukoencephalopathy and basal ganglia abnormalities. The third patient showed a slow neurodegenerative condition with global brain atrophy and the fourth patient showed Leigh-like lesions with a single episode of metabolic acidosis. Clinical picture and metabolite analysis were not consistent with a mitochondrial fatty acid oxidation disorder, which was supported by the normal palmitate loading test in fibroblasts. Patient fibroblasts displayed deficient hydratase activity with different substrates tested. Pyruvate dehydrogenase activity was markedly reduced in particular in muscle from the most severely affected patients, which was caused by reduced expression of E2 protein, whereas E2 mRNA was increased.ConclusionsDespite its activity towards substrates from different metabolic pathways, SCEH appears to be only crucial in valine metabolism, but not in isoleucine metabolism, and only of limited importance for mitochondrial fatty acid oxidation. In severely affected patients SCEH deficiency can cause a secondary pyruvate dehydrogenase deficiency contributing to the clinical presentation.Electronic supplementary materialThe online version of this article (doi:10.1186/s13023-015-0290-1) contains supplementary material, which is available to authorized users.

Clinical, biochemical, and genetic features of four patients with short‐chain enoyl‐CoA hydratase (ECHS1) deficiency

“…In primary 3‐MGA, deficiency of 3‐methyl glutaconyl Co A hydratase due to mutations in the AUH gene are directly responsible for the accumulation of 3MGC while in secondary 3MGA, no defect in leucine catabolism exists and the metabolic origin of 3MGC is unknown (Su & Ryan, 2014). Increased 3‐HIVA has been previously reported in a 1‐year‐old male patient (Ferdinandusse et al, 2015) and increased excretion of 3‐MGC has been reported previously in at least one case of SCEH deficiency, a 7‐year‐old female and may represent a later biochemical feature in milder cases (Ferdinandusse et al, 2015) and noted to be increased transiently following long‐term follow‐up (Huffnagel et al, 2017). All of our patients were from consanguineous unions so it is possible that excretion of 3‐MGC is not related to ECHS1 mutations but to a separate condition or secondary to mitochondrial dysfunction.…”

“…All four patients had increased excretion of erythro ‐2,3‐dihydroxy‐2‐methylbutyrate; this metabolite derived from acryloyl‐CoA was originally described in SCEH deficiency in 2014 by Peters et al Latter patient reports document concentrations of varying magnitude (Bedoyan et al, 2017; Ferdinandusse et al, 2015; Peters et al, 2015) and that levels may be unreliable shortly after birth (Ganetzky et al, 2016) which was the case in Patient 4. Two out of four patients had increased methylmalonic acid which has been reported previously in a patient with SCEH deficiency (Tetreault et al, 2015).…”

“…SCEH enzyme activity was markedly reduced in fibroblasts of Patient 1 (40 nmol/(min.mg protein)) and Patient 3 (27 nmol/[min.mg protein]) compared to the reference values (199–670 nmol/[min.mg protein]). Immunodetection of steady‐state SCEH protein in fibroblast homogenates of Patient 1 and 3 by western blotting revealed the absence of the 27 kDa band corresponding to SCEH (Ferdinandusse et al, 2015). …”

“…SCEH activity in cultured fibroblasts was markedly reduced but not completely deficient, which is in agreement with a milder clinical phenotype considering the age of death when compared to some other published cases (Bedoyan et al, 2017; Haack et al, 2015; Peters et al, 2014). Ferdinandusse et al investigated the role of SCEH in fatty acid and branched‐chain amino acid metabolism in four patients with mutations in ECHS1 and results from their enzyme activity measurements and immunoblot analysis strongly suggest that there is a correlation between the residual SCEH enzyme activity and the severity of the clinical symptoms (Ferdinandusse et al, 2015). In addition, excretion of 2,3‐dihydroxy‐2‐methylbutyrate may not have been reported or checked in some historical cases because its significance was not known at the time; it may be a more common biochemical feature of SCEH deficiency than we are aware of.…”

“…While the exact origin of 2‐methyl‐2,3‐dihydroxybutyrate is currently unknown, we previously noted this metabolite in patients with lactic acidosis of unknown etiology, and in patients with genetically proven metabolic disorders including glycogen storage disease type 1a (OMIM 232200), propionic acidemia (propionyl‐CoA carboxylase deficiency, OMIM 232000), methylmalonic aciduria (methylmalonyl‐CoA mutase deficiency, OMIM 251000), PDH deficiency (OMIM 300502), and multiple carboxylase deficiency due to biotinidase deficiency (OMIM 609019). Despite complete deficiencies of the enzymatic activities in fibroblasts, Ferdinandusse and co‐workers could not detect 2,3‐dihydroxy‐2‐methylbutyrate in the supernatant of patients' cultured fibroblasts (Ferdinandusse et al, 2015). 2,3‐dihydroxy‐2‐methylbutyrate exists as two isomers, erythro and threo .…”