[Clinical characteristics analysis of mitochondrial short-chain enoyl-CoA hydratase 1 deficiency with ECHS1 gene c.489G>A compound heterozygous variants]

Objective: To summarize the clinical characteristics of children with mitochondrial short-chain enoyl-CoA hydratase-1 deficiency (ECHS1D) caused by c.489G>A (p.Pro163=) compound heterozygous variants in the ECHS1 gene, and to explore genotype-phenotype correlations. Methods: A case series study was performed to analyze clinical, biochemical, metabolic, imaging, genetic, treatment and follow-up outcomes of 24 children with ECHS1 gene c.489G>A(p.Pro163=) variant, who were diagnosed in the Department of Neurology, Beijing Children's Hospital from July 2010 to June 2024. Disease severity was assessed using the Newcastle Paediatric Mitochondrial Disease Scale, and Fisher exact test was applied to compare the improvement rate between valine-restricted and non-restricted groups. Results: These 24 children were all diagnosed after 2022, with a disease duration of 3.35 (1.25, 6.52) years at diagnosis. A total of 8 children initially had negative genetic results, and were finally confirmed by abnormal splicing of ECHS1 gene via skin fibroblast RNA sequencing, with the longest diagnostic time of 14 years. All 24 children presented with Leigh syndrome, including 11 boys and 13 girls, with an onset age of 1.46 (0.96, 2.79) years; 16 children (67%) were mild cases. Common initial symptoms included developmental delay (9 cases) and paroxysmal dystonia (9 cases), followed by developmental regression (3 cases), nystagmus (2 cases), and epilepsy (1 case). Main manifestations were dystonia (18 cases), developmental regression (14 cases), nystagmus (12 cases), developmental delay (11 cases), ataxia (10 cases), vision loss (9 cases), seizures (2 cases), and hearing impairment (1 case). Among 22 children who underwent blood and urine metabolic screening, 21 children (95%) had elevated urinary 2, 3-dihydroxy-2-methylbutyric acid and 19 children (86%) had elevated urinary S-(2-hydroxypropyl) cysteamine. All 24 children had symmetric abnormal signals in bilateral globus pallidus on cranial magnetic resonance imaging, 10 children had isolated globus pallidus involvement, and other common involved sites included caudate nucleus and brainstem (9 cases each), putamen (7 cases), and cerebral white matter (5 cases). At last follow-up, all 24 children survived, with a follow-up duration of 5.40 (2.75, 8.02) years and a maximum age of 17.8 years; 17 children (71%) had varying degrees of clinical improvement. There was no statistical difference in the improvement rate between children with or without valine-restricted diet (12/14 vs. 5/8,P=0.309). A total of 18 pathogenic variants in the ECHS1 gene were identified among 24 children, 13 of which were distributed in exons 7 and 8; those carrying c.308T>C, c.523G>A, c.796A>G, and c.832G>A variants were mostly severe cases. Conclusions: Children carrying ECHS1 gene c.489G>A(p.Pro163=) compound heterozygous variants face significant diagnostic delay. Clinical awareness of this synonymous variant needs further improvement for timely diagnosis. All these cases present as Leigh syndrome, mostly mild, with no clear genotype-phenotype correlation identified.