ATM NM_000051.3:c.1158del, Lys387ArgfsTer3

Variant summary: ATM c.1158delG (p.Lys387ArgfsX3) results in a premature termination codon, predicted to cause a truncation of the encoded protein or absence of the protein due to nonsense mediated decay, which are commonly known mechanisms for disease. Truncations downstream of this position have been classified as pathogenic by our laboratory (c.1339C>T, p.Arg447X; c.1564_1565delGA, p.Glu522fsX43; c.2502dupA, p.Val835fsX7). The variant was absent in 251274 control chromosomes (gnomAD). The variant, c.1158delG, has been reported in the literature in multiple individuals affected with Ataxia-Telangiectasia (Izatt_1999, Thompson_2005, Nahas_2009, Schon_2019). These data indicate that the variant is likely to be associated with disease. To our knowledge, no experimental evidence demonstrating an impact on protein function has been reported. Three ClinVar submissions from other clinical diagnostic laboratories (evaluation after 2014) cite the variant as pathogenic. Based on the evidence outlined above, the variant was classified as pathogenic.

The c.1158delG pathogenic mutation, located in coding exon 8 of the ATM gene, results from a deletion of one nucleotide at nucleotide position 1158, causing a translational frameshift with a predicted alternate stop codon (p.K387Rfs*3). This mutation has been identified in trans with another ATM mutation in patients with ataxia-telangiectasia (Izatt L et al. Eur. J. Hum. Genet., 1999 Apr;7:310-20; Schon K et al. Ann Neurol, 2019 02;85:170-180). This variant is considered to be rare based on population cohorts in the Genome Aggregation Database (gnomAD). In addition to the clinical data presented in the literature, this alteration is expected to result in loss of function by premature protein truncation or nonsense-mediated mRNA decay. As such, this alteration is interpreted as a disease-causing mutation.

This sequence change creates a premature translational stop signal (p.Lys387Argfs*3) in the ATM gene. It is expected to result in an absent or disrupted protein product. Loss-of-function variants in ATM are known to be pathogenic (PMID: 23807571, 25614872). This variant is not present in population databases (gnomAD no frequency). This premature translational stop signal has been observed in individual(s) with ataxia-telangiectasia (PMID: 10234507). In at least one individual the data is consistent with being in trans (on the opposite chromosome) from a pathogenic variant. ClinVar contains an entry for this variant (Variation ID: 141887). For these reasons, this variant has been classified as Pathogenic.