ClinVar

Description

The c.3151G>A (p.G1051R) alteration is located in exon 20 (coding exon 19) of the POLG gene. This alteration results from a G to A substitution at nucleotide position 3151, causing the glycine (G) at amino acid position 1051 to be replaced by an arginine (R). Based on the available evidence, this variant is classified as likely pathogenic for autosomal recessive POLG-related mitochondrial disorders; however, the clinical significance for autosomal dominant POLG-related progressive external ophthalmoplegia is unclear. Based on data from gnomAD, the A allele has an overall frequency of 0.001% (2/282698) total alleles studied. This variant has been confirmed in trans with a second POLG variant in a patient with Alpers syndrome (Li, 2021). It has also been observed in the homozygous state in an individual from a large autism cohort; however, no details were provided regarding whether the patient had clinical symptoms of a POLG-related disorder (Doan, 2019)._x000D_ _x000D_ A different nucleotide substitution resulting in the same missense change, c.3151G>C (p.G1051R), has been previously reported in the compound heterozygous state with other POLG variants in multiple individuals with autosomal recessive POLG-related disorders (Mancuso, 2004; Formichi, 2016; Da Pozzo, 2017). This amino acid position is well conserved in available vertebrate species. Based on internal structural analysis, G1051R is highly destabilizing to the local structure (Ambry internal data). Functional studies using yeast models have shown that G1051R causes increased mtDNA instability and mutant frequency, indicative of defects in the mtDNA genome (Baruffini, 2007; Baruffini, 2010; Stumpf, 2010). This alteration is predicted to be deleterious by in silico analysis. Based on the available evidence, this alteration is classified as likely pathogenic.