The NM_000018.4:c.770del (p.Asp257AlafsTer19) variant in ACADVL is a frameshift variant predicted to cause a premature stop codon in biologically relevant exon 9/20 leading to nonsense mediated decay in a gene in which loss-of-function is an established disease mechanism (PVS1; PMIDs 9973285, 11590124). At least one individual with this variant was identified by newborn screen, but this information is insufficient to use toward classification (PMID: 30194637, 20547398). Additionally, this variant was identified in an individual who reportedly had increased acylcarnities and decreased very long chain acyl-CoA dehydrogenase (VLCAD) activity, but this information was insufficient to use toward classification (PMID: 12682504). This variant is absent from gnomAD v2.1.1 (PM2_supporting). In summary, this variant meets the criteria to be classified as likely pathogenic for autosomal recessive VLCAD deficiency based on the ACMG/AMP criteria applied, as specified by the ClinGen ACADVL Variant Curation Expert Panel: PVS1, PM2_Supporting (ACADVL VCEP specifications version 1; approved November 8, 2021).