ClinVar Genomic variation as it relates to human health

Variant summary: IDUA c.152G>A (p.Gly51Asp) results in a non-conservative amino acid change in the encoded protein sequence. Five of five in-silico tools predict a damaging effect of the variant on protein function. The variant allele was found at a frequency of 9.2e-06 in 109252 control chromosomes (gnomAD). c.152G>A has been reported in the literature in multiple individuals (both homozygous and compound heterozygous) affected with Mucopolysaccharidosis Type 1 (Bertola_2011, Bunge_1994, Amr_2009). Many of these patients, had a severe phenotype. These data indicate that the variant is very likely to be associated with disease. Three ClinVar submissions (evaluation after 2014) cite the variant as pathogenic. Based on the evidence outlined above, the variant was classified as pathogenic.

The p.Gly51Asp variant in IDUA has been reported in at least 15 individuals with mucopolysaccharidosis (MPS) (PMID: 7951228, 19839758, 12203999, 21394825) and has been identified in 0.002% (1/40612) of European (non-Finnish) chromosomes by the Genome Aggregation Database (gnomAD, http://gnomad.broadinstitute.org; dbSNP rs794726877). Although this variant has been seen in the general population, its frequency is not high enough to rule out a pathogenic role. This variant has also been reported in ClinVar (VariationID: 193061) as pathogenic by EGL Genetic Diagnostics, Counsyl, and GeneReviews. In vitro functional studies provide some evidence that the p.Gly51Asp variant may slightly impact protein function (PMID: 9748610). 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 phenotype of an individual compound heterozygous for this variant is highly specific for MPS based on significantly reduced alpha-L-iduronidase activity levels consistent with disease (PMID: 9748610). Additionally, the presence of this variant in at least 3 affected homozygotes and in combination with reported pathogenic variants in at least 8 individuals with MPS increases the likelihood that the p.Gly51Asp variant is pathogenic (VariationID: 11908, 11909, 11910, 496861; PMID: 7951228, 19839758, 12203999, 21394825). In summary, this variant meets criteria to be classified as pathogenic for MPS in an autosomal recessive manner based on the presence of the variant in combination with other pathogenic variants in individuals with MPS, functional studies, and the phenotype of patients with the variant being highly specific for IDUA. ACMG/AMP Criteria applied: PM3_very-strong, PM2, PP3, PP4, PS3_supporting (Richards 2015).

This sequence change replaces glycine, which is neutral and non-polar, with aspartic acid, which is acidic and polar, at codon 51 of the IDUA protein (p.Gly51Asp). The frequency data for this variant in the population databases is considered unreliable, as metrics indicate poor data quality at this position in the gnomAD database. This missense change has been observed in individual(s) with mucopolysaccharidosis type I (MPS I) (PMID: 7951228, 9427149, 12203999, 19839758, 21394825). ClinVar contains an entry for this variant (Variation ID: 193061). Advanced modeling of protein sequence and biophysical properties (such as structural, functional, and spatial information, amino acid conservation, physicochemical variation, residue mobility, and thermodynamic stability) has been performed at Invitae for this missense variant, however the output from this modeling did not meet the statistical confidence thresholds required to predict the impact of this variant on IDUA protein function. For these reasons, this variant has been classified as Pathogenic.

Common pathogenic variant in Italy