Published functional studies demonstrate a damaging effect due to improper intracellular localization of pendrin and loss of pendrin-induced iodide and chloride transport (Scott et al., 2000; Yoon et al., 2008); Common variant in Caucasian populations, accounting for approximately 10% of pathogenic alleles in published studies of Western European individuals (Tsukada et al., 2015); In silico analysis, which includes protein predictors and evolutionary conservation, supports a deleterious effect; This variant is associated with the following publications: (PMID: 22975760, 26969326, 11317356, 31827275, 12354788, 10861298, 18310264, 9618166, 26022370, 10700480, 20553101, 9618167, 22717225, 27771369, 31163360, 15689455, 20597900, 25999548, 31980526, 31589614)

Variant summary: SLC26A4 c.707T>C (p.Leu236Pro) 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 0.00027 in 251476 control chromosomes. This frequency is not significantly higher than estimated for a pathogenic variant in SLC26A4 causing Pendred Syndrome (0.00027 vs 0.0035), allowing no conclusion about variant significance. c.707T>C has been reported in the literature in multiple homozygous and compound heterozygous individuals affected with Pendred Syndrome (e.g. Rendtorff_2013, Scott_2000). These data indicate that the variant is very likely to be associated with disease. At least one publication reports experimental evidence evaluating an impact on protein function. The most pronounced variant effect results in loss of pendrin-induced chloride and iodide transport (e.g. Scott_2000). The following publications have been ascertained in the context of this evaluation (PMID: 23336812, 10861298). ClinVar contains an entry for this variant (Variation ID: 4817). Based on the evidence outlined above, the variant was classified as pathogenic.

The c.707T>C (p.L236P) alteration is located in exon 6 (coding exon 5) of the SLC26A4 gene. This alteration results from a T to C substitution at nucleotide position 707, causing the leucine (L) at amino acid position 236 to be replaced by a proline (P). Based on data from gnomAD, the C allele has an overall frequency of 0.029% (83/282766) total alleles studied. The highest observed frequency was 0.06% (77/129104) of European (non-Finnish) alleles. This variant has been identified in the homozygous state and in conjunction with other SLC264 variants in individuals with features consistent with SLC26A4-related deafness; in at least one instance, the variants were identified in trans (Van Hauwe, 1998; Downie, 2020; Badyga, 2023). Another variant at the same codon, c.706C>G (p.L236V), has been identified in individuals with features consistent with SLC26A4-related deafness (Chiong, 2018). This amino acid position is well conserved in available vertebrate species. This alteration is predicted to be deleterious by in silico analysis. Based on the available evidence, this alteration is classified as pathogenic.

The c.707T>C variant in SLC26A4 is a missense variant predicted to cause substitution of leucine to proline at amino acid 236. This variant is rare in the general population with a frequency below the threshold expected for the associated phenotype(s). This variant has been observed in one or more individuals affected with the associated recessive disease, as either homozygous or compound heterozygous with a second variant (PMID: 23336812). Given the available evidence, this variant is classified as Pathogenic.

The SLC26A4 c.707T>C (p.Leu236Pro) missense variant is well described in the literature and is one of the three most common pathogenic variants in SLC26A4, which together account for 50% of the disease-causing alleles in probands with Pendred syndrome of northern European descent (Alasti et al. 2014; Tsukada et al. 2015). Across a selection of available literature, the p.Leu236Pro variant has been reported in at least four individuals in a homozygous state, 13 individuals in a compound heterozygous state, and one individual in a heterozygous state, all affected with Pendred syndrome (van Hauwe et al. 1998; Coyle et al. 1998; Campbell et al. 2001). The variant has also been reported in individuals affected with hearing loss, including two in a compound heterozygous state and five in a heterozygous state (Yan et al. 2017). Campbell et al. (2001) demonstrated segregation with disease in at least one multiplex family with temporal bone abnormalities. Haplotype analysis suggests a common founder effect for this variant (van Hauwe et al. 2008; Coyle et al. 1998). The p.Leu236Pro variant was absent from 257 control individuals (van Hauwe et al. 1998; Coyle et al. 1998; Campbell et al. 2001; Yan et al. 2017) and is reported at a frequency of 0.00105 in the European American population of the Exome Sequencing Project. Functional studies by Rotman-Pikielny et al. (2002) demonstrated that the variant protein is retained in the endoplasmic reticulum (ER) whereas the wild type protein targets to the plasma membrane. Yoon et al. (2008) confirmed the initial localization of the p.Leu236Pro variant protein in the ER and showed that after time, the protein was concentrated at the centrosome. They further determined that Cl-/HCO3- ion exchange activity of the variant protein was notably decreased, and that the variant was not temperature sensitive. Based on collective evidence, the p.Leu236Pro variant is classified as pathogenic for SLC26A4-related disorders. This variant was observed by ICSL as part of a predisposition screen in an ostensibly healthy population.

NM_000441.1(SLC26A4):c.707T>C(L236P) is classified as pathogenic in the context of Pendred syndrome. Sources cited for classification include the following: PMID 9618167, 9618166, 18310264 and 12354788. Classification of NM_000441.1(SLC26A4):c.707T>C(L236P) is based on the following criteria: This is a well-established pathogenic variant in the literature that has been observed more frequently in patients with clinical diagnoses than in healthy populations. Please note: this variant was assessed in the context of healthy population screening.

PS1_Strong, PM2_Supporting, BP4_Supporting

PM2_supporting, PP3_supporting, PS3_supporting, PM3_very-strong, PP4_supporting

The p.Leu236Pro variant in SLC26A4 has been reported in at least 15 individuals with either nonsyndromic hearing loss or Pendred syndrome who were homozygous or compound heterozygous, and it segregated in 4 affected family members from 2 fa milies (Busi 2012, Pryor 2005, Pourova 2010, Siem 2010, Van Hauwe 1998, LMM data ). One in vitro functional analysis study suggests the variant may impact normal intracellular trafficking of the protein (Rotman-Pikielny 2002). The p.Leu236Pr o variant has been identified in 0.1% (78/126638) of European chromosomes by the Genome Aggregation Database (gnomAD, http://gnomad.broadinstitute.org; dbSNP rs 80338848). Although this variant has been seen in the general population, its fr equency is low enough to be consistent with a recessive carrier frequency. In su mmary, this variant meets criteria to be classified as pathogenic for autosomal recessive hearing loss based on bi-allelic occurrences in multiple affected indi viduals, segregation studies, functional evidence, and low frequency in the gene ral population. ACMG/AMP criteria applied: PM3_VeryStrong, PP1_Moderate, PS3_Sup porting.

Based on the classification scheme VCGS_Germline_v1.3.4, this variant is classified as Pathogenic. Following criteria are met: 0102 - Loss of function is a known mechanism of disease in this gene and is associated with Pendred syndrome (MIM#274600). (I) 0106 - This gene is associated with autosomal recessive disease. (I) 0115 - Variants in this gene are known to have variable expressivity (PMID: 20301640). (I) 0200 - Variant is predicted to result in a missense amino acid change from leucine to proline. (I) 0251 - This variant is heterozygous. (I) 0304 - Variant is present in gnomAD <0.01 for a recessive condition (v2: 83 heterozygotes, 0 homozygotes). (SP) 0309 - An alternative amino acid change at the same position has been observed in gnomAD (v2) (12 heterozygotes, 0 homozygotes). (I) 0501 - Missense variant consistently predicted to be damaging by multiple in silico tools or highly conserved with a major amino acid change. (SP) 0600 - Variant is located in the annotated sulfate permease family (DECIPHER). (I) 0801 - This variant has very strong previous evidence of pathogenicity in unrelated individuals. It is one of the three most common variants in individuals with European descent with Pendred syndrome or deafness 4 with enlarged vestibular aqueduct (ClinVar, PMID: 20301640). (SP) 1102 - Strong phenotype match for this individual. (SP) 1208 - Inheritance information for this variant is not currently available in this individual. (I) Legend: (SP) - Supporting pathogenic, (I) - Information, (SB) - Supporting benign

PP3, PM2_supporting, PM3_very_strong, PM5, PS3

This sequence change replaces leucine, which is neutral and non-polar, with proline, which is neutral and non-polar, at codon 236 of the SLC26A4 protein (p.Leu236Pro). This variant is present in population databases (rs80338848, gnomAD 0.06%). This missense change has been observed in individual(s) with Pendred syndrome and hearing loss (PMID: 9618166, 15689455, 20553101, 20597900, 26969326). In at least one individual the data is consistent with being in trans (on the opposite chromosome) from a pathogenic variant. ClinVar contains an entry for this variant (Variation ID: 4817). Invitae Evidence Modeling of protein sequence and biophysical properties (such as structural, functional, and spatial information, amino acid conservation, physicochemical variation, residue mobility, and thermodynamic stability) indicates that this missense variant is expected to disrupt SLC26A4 protein function with a positive predictive value of 95%. Experimental studies have shown that this missense change affects SLC26A4 function (PMID: 10861298, 12354788, 18310264). For these reasons, this variant has been classified as Pathogenic.

SLC26A4: PM3:Very Strong, PM2, PM5, PP3, PS3:Supporting

The SLC26A4 p.L236P variant has been reported in multiple homozygous or compound heterozygous individuals with hearing loss or hearing impairment (Yan_2017_PMID:28273078; Tang_2015_PMID:25991456; Pryor_2005_PMID:15689455; Pourova_2010_PMID:20597900; Busi_2012_PMID:22717225; Campbell_2001_PMID:11317356; Siem_2010_PMID:20553101; Van Hauwe_1998_PMID:9618166). The variant was identified in dbSNP (ID: rs80338848) and ClinVar (classified as pathogenic by Invitae, GeneDx, EGL Genetic Diagnostics and nine other submitters). The variant was identified in control databases in 83 of 282766 chromosomes (0 homozygous) at a frequency of 0.0002935, and was observed at the highest frequency in the European (non-Finnish) population in 77 of 129104 chromosomes (freq: 0.0005964) (Genome Aggregation Database March 6, 2019, v2.1.1). The p.L236 residue is conserved in mammals and computational analyses (MUT Assesor, PolyPhen-2, SIFT, MutationTaster, Revel, FATHMM, MetaLR, DANN) suggest that the variant may impact the protein; however, this information is not predictive enough to assume pathogenicity. Functional studies have shown that this variant causes protein mislocalization and impaired iodide/chloride transport activity compared to wild type (Scott_2000_PMID:10861298, Rotman-Pikielny_2002_PMID:12354788, Yoon_2008_PMID:18310264). The variant occurs outside of the splicing consensus sequence and in silico or computational prediction software programs (Splice AI exome) do not predict a difference in splicing. In summary, based on the above information this variant meets our laboratory’s criteria to be classified as pathogenic.

The SLC26A4 c.707T>C variant is predicted to result in the amino acid substitution p.Leu236Pro. This variant has been reported to be causative for Pendred syndrome (van Hauwe et al 1998. PubMed ID: 9618166; Campbell et al 2001. PubMed ID: 11317356; Pourová et al 2010. PubMed ID: 20597900). This variant is reported in 0.060% of alleles in individuals of European (Non-Finnish) descent in gnomAD. This variant is interpreted as pathogenic.