ClinVar Genomic variation as it relates to human health

The p.Leu238Gln variant in IDUA has been reported in at least 7 individuals with mucopolysaccharidosis (MPS), segregated with disease in 4 affected relatives from 2 families (PMID: 24368159), and has been Identified in 0.014% (2/13914) of African chromosomes and 0.003% (3/102956) of European (non-Finnish) chromosomes by the Genome Aggregation Database (gnomAD, http://gnomad.broadinstitute.org; dbSNP rs148789453). Although this variant has been seen in the general population, its frequency is low enough to be consistent with a recessive carrier frequency. In vitro functional studies provide some evidence that the p.Leu238Gln variant may impact protein function (PMID: 15300847). 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 in 5 individuals with MPS increases the likelihood that the p.Leu238Gln variant is pathogenic (VariationID: 11908, 222994; PMID: 24368159). The phenotype of individuals compound heterozygous for this variant is highly specific for MPS based on alpha-L-iduronidase activity being <1%, consistent with disease (PMID: 15300847). 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 known pathogenic variants, functional studies, cosegregation, and the phenotype of individuals with the variant and MPS being highly specific for IDUA. ACMG/AMP Criteria applied: PM3_strong, PS3_moderate, PM2_supporting, PP3, PP4, PP1 (Richards 2015).

Published functional studies demonstrate that the L238Q variant causes reduced IDUA activity and protein levels when expressed in Chinese hamster ovary (CHO) cells (Yogalingam et al., 2004); In silico analysis, which includes protein predictors and evolutionary conservation, supports a deleterious effect; Not observed at significant frequency in large population cohorts (gnomAD); This variant is associated with the following publications: (PMID: 15300847, 24368159, 26260077, 31194252)

This sequence change replaces leucine, which is neutral and non-polar, with glutamine, which is neutral and polar, at codon 238 of the IDUA protein (p.Leu238Gln). This variant is present in population databases (rs148789453, gnomAD 0.008%). This missense change has been observed in individual(s) with mucopolysaccharidosis type I (PMID: 15300847, 24368159; Invitae). ClinVar contains an entry for this variant (Variation ID: 265418). 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) performed at Invitae indicates that this missense variant is expected to disrupt IDUA protein function with a positive predictive value of 95%. This variant disrupts the p.Leu238 amino acid residue in IDUA. Other variant(s) that disrupt this residue have been observed in individuals with IDUA-related conditions (PMID: 21480867, 24368159), which suggests that this may be a clinically significant amino acid residue. For these reasons, this variant has been classified as Pathogenic.

The IDUA c.713T>A variant is predicted to result in the amino acid substitution p.Leu238Gln. This variant was reported along with second variant in several individuals with Mucopolysaccharidosis type 1 (Yogalingam et al. 2004. PubMed ID: 15300847; Ahmed et al. 2013. PubMed ID: 24368159). In vitro functional study demonstrated that this variant reduces IDUA activity to 5.88% of normal enzyme activity (Table 3, Yogalingam et al. 2004. PubMed ID: 15300847). Alternative variant at the same codon p.Leu238Arg has been observed in an individual with Mucopolysaccharidosis type 1 (Wang et al. 2011. PubMed ID: 21480867). This variant is reported in 0.014% of alleles in individuals of African descent in gnomAD. This variant is interpreted as pathogenic.