rs121908680
- Conflicting interpretations of pathogenicity
Your Genotype
Sign InDescription
Functional studies demonstrate that this variant significantly impairs catalytic activity of the PLA2G6 protein (Engel et al., 2010); Nonsense variant in the C-terminus predicted to result in protein truncation, as the last 17 amino acids are lost, and other loss-of-function variants have been reported downstream in the Human Gene Mutation Database (Stenson et al., 2014); This variant is associated with the following publications: (PMID: 18359254, 20886109, 16783378, 27378808, 28600779, 24800972, 18443314, 24847269, 18570303, 24745848, 30537300, 30340910, 20619503, 33101984, 31589614)
This variant was determined to be pathogenic according to ACMG Guidelines, 2015 [PMID:25741868]. This variant has been previously reported as disease-causing [PMID 16783378, 27378808, 20886109]
The PLA2G6 c.2370T>G (p.Tyr790Ter) variant is a stop-gained variant and has been reported in at least eight studies in a total of 11 probands with PLA2G6-associated neurodegeneration, including in at least five in a homozygous state, in five in a compound heterozygous state, and in one in a heterozygous state (Morgan et al. 2006; Carrilho et al. 2008; Gregory et al. 2008; Pinto et al. 2010; Paisan-Ruiz 2012; Illingworth et al. 2014; Blake et al. 2016; Erro et al. 2016). Of note, another variant, c.2370_2371delTG, which also results in p.Tyr790Ter, has been reported in both a homozygous and compound heterozygous state in other probands. Control data are not available for the p.Tyr790Ter variant, which is reported at a frequency of 0.000148 in the Latino from the Genome Aggregation Database. In vitro studies examining the catalytic function of the p.Tyr790Ter variant demonstrated <10% phospholipase activity compared to wildtype in the presence of two different substrates (Engel et al. 2010). Based on the collective evidence, the p.Tyr790Ter variant is classified as pathogenic for PLA2G6-associated neurodegeneration. This variant was observed by ICSL as part of a predisposition screen in an ostensibly healthy population.
We were able to detect the known pathogenic mutation c.2370T>G in the PLA2G6 gene in the patient in a heterozygous state. The variant was also detected in the mother of the patient in heterozygous state. The PLA2G6 gene codes for phospholipase A2 of group 6 (MIM *603604). Biallelic pathogenic sequence variants in PLA2G6 have been described with three clinical manifestations of autosomal recessively inherited PLA2G6-associated neurodegeneration: 1) infantile neuroaxonal dystrophy (INAD, MIM: 256600), 2) neurodegeneration with iron accumulation in the brain (NBIA, MIM: 610217) and 3) PLA2G6-dependent dystonia parkinsonism (MIM: 612953). Clinical symptoms include psychomotor regression, symmetrical pyramidal trajectory signs, pronounced trunk hypotension, spastic quadriplegia, visual disturbances and dementia. The clinical course may be variable. The above variation leads to the formation of a premature stop codon and thus most likely to the premature termination of protein biosynthesis. The variant has already been reported in numerous patients in homozygous or compound-heterozygous condition (HGMD: CM063050). The sequence variant is listed in gnomAD 25x in heterozygous state and occurs in the European subpopulation with an allele frequency of 0.015%.
This variant has been previously reported as disease-causing and was found twice in our laboratory with another variant in affected individuals: a 2-year-old male with regression, hearing loss, hypotonia, failure to thrive, cerebellar atrophy, vision loss; a 5-year-old female with regression, dystonia, epilepsy, microcephaly, failure to thrive, cerebellar atrophy. Heterozygotes would be expected to be asymptomatic carriers.
This sequence change creates a premature translational stop signal (p.Tyr790*) in the PLA2G6 gene. While this is not anticipated to result in nonsense mediated decay, it is expected to disrupt the last 17 amino acid(s) of the PLA2G6 protein. This variant is present in population databases (rs121908680, gnomAD 0.01%). This premature translational stop signal has been observed in individuals with clinical features of PLA2G6-related conditions (PMID: 16783378, 27378808; Invitae). ClinVar contains an entry for this variant (Variation ID: 6195). Algorithms developed to predict the effect of variants on protein structure and function are not available or were not evaluated for this variant. Experimental studies have shown that this premature translational stop signal affects PLA2G6 function (PMID: 20886109). Algorithms developed to predict the effect of sequence changes on RNA splicing suggest that this variant may create or strengthen a splice site. For these reasons, this variant has been classified as Pathogenic.
Reference Allele
A
Alternative Allele
C
Chromosome
22
Location
38112212
Variant Type
SNP
ClinVar
Name
NM_003560.4(PLA2G6):c.2370T>G (p.Tyr790Ter)
Allele
C
Clinical Significance
Conflicting interpretations of pathogenicity