ClinVar Genomic variation as it relates to human health

The c.667T>C (p.W223R) alteration is located in exon 7 (coding exon 6) of the GBA gene. This alteration results from a T to C substitution at nucleotide position 667, causing the tryptophan (W) at amino acid position 223 to be replaced by an arginine (R). Based on data from gnomAD, the C allele has an overall frequency of <0.01% (2/251106) total alleles studied. The highest observed frequency was <0.01% (2/113588) of European (non-Finnish) alleles. This alteration, also referred to as p.W184R in the literature, has been reported in the compound heterozygous state with a second mutation in multiple patients with Gaucher disease (Amaral, 2000; Choy, 2000; Rozenberg, 2006; Panicker, 2014; Dimitriou, 2020). This amino acid position is highly conserved in available vertebrate species. Expression studies in Sf9 cells showed very low activity and an essentially inactive protein (Amaral, 2000). Human induced pluripotent stem cells from fibroblasts of an affected patient with this alteration and a second alteration showed low levels of beta-glucocerebrosidase activity and widespread lysosomal depletion and dysfunction (Panicker, 2014; Awad, 2015). This alteration is predicted to be deleterious by in silico analysis. Based on the available evidence, this alteration is classified as pathogenic.

Variant summary: The GBA c.667T>C (p.Trp223Arg) variant causes a missense change involving the alteration of a non-conserved nucleotide and it is located in the Glycosyl hydrolase family 30, TIM-barrel domain (IPR033453) (InterPro). 5/5 in silico tools predict a damaging outcome for this variant. This was confirmed by functional studies showing abrogated Beta-glucosidase catalytic activity (0.0004 total units of specific activity per cross-reacting immunologic material (CRIM SA) (vs. 1 in control) (Amaral_2000, Awad_2015). This variant was found in 3/112128 control chromosomes at a frequency of 0.0000268, which does not exceed the estimated maximal expected allele frequency of a pathogenic GBA variant (0.005). This variant was reported in multiple patients with Gaucher disease (Choy_1999, Rozenberg_2006) in which pseudogene interference was ruled out. In addition, multiple clinical diagnostic laboratories/reputable databases classified this variant as pathogenic. Taken together, this variant is classified as pathogenic.

The p.Trp223Arg variant in GBA has been reported in at least 8 individuals with Gaucher disease (PMID: 17059888, 24801745, 27136700, 10679038, 27864021) and has been Identified in 0.002% (2/111560) of European (non-Finnish) chromosomes by the Genome Aggregation Database (gnomAD, http://gnomad.broadinstitute.org; dbSNP rs61748906). Although this variant has been seen in the general population, its frequency is low enough to be consistent with a recessive carrier frequency. This variant has also been reported in ClinVar (VariationID: 93457) as benign by Prevention Genetics, likely pathogenic by Praxis fuer Humangenetik Tuebingen, and pathogenic by Integrated Genetics and EGL Genetic Diagnostics. In vitro functional studies demonstrating very low glucocerebrosidase activity in mutant hiPSC macrophages provide some evidence that the p.Trp223Arg variant may impact protein function (PMID: 24801745). However, these types of assays may not accurately represent biological function. Computational prediction tools and conservation analyses suggest that this variant may impact the protein, though this information is not predictive enough to determine pathogenicity. The presence of this variant in combination with reported pathogenic variants and in 8 individuals with Gaucher disease increases the likelihood that the p.Trp223Arg variant is pathogenic (VariationID: 4288, 4290, 4293; PMID: 17059888, 24801745, 27136700, 10679038, 27864021). In summary, this variant meets criteria to be classified as pathogenic for Gaucher disease in an autosomal recessive manner based on the presence of the variant in combination with other pathogenic variants in affected individuals, functional studies, and the low frequency of the variant in the general population. ACMG/AMP Criteria applied: PM3_very-strong, PM2, PS3_moderate, PP3 (Richards 2015).

Functional studies found that W223R is associated with significantly reduced enzyme activity (PMID: 10757640); In silico analysis supports that this missense variant has a deleterious effect on protein structure/function; This variant is associated with the following publications: (PMID: 9516376, 25435509, 8889578, 11112377, 18078074, 10679038, 27864021, 16396828, 29198828, 26220978, 16418594, 18070135, 24904648, 30606667, 32658388, 34586679, 17059888, 33301762, 10757640)