ClinVar Genomic variation as it relates to human health

This PKHD1 variant (rs200511261) is rare (<0.1%) in a large population dataset (gnomAD: 13/250878 total alleles; 0.005%; no homozygotes) and has an entry in ClinVar. It has been observed on the opposite chromosome from other pathogenic variants in individuals affected with PKD4. Two bioinformatics tools queried predict that p.Ile3177Thr would be tolerated, while another predicts it would be damaging. The isoleucine residue at this position is partially conserved across the vertebrate species assessed; some species have a valine substitution at this position. This variant is not predicted to affect normal exon 58 splicing, although this has not been confirmed experimentally to our knowledge. We consider c.9530T>C to be likely pathogenic.

PM2, PM3, PP1, PP4, PP5

Not observed at a significant frequency in large population cohorts (Lek et al., 2016); In silico analysis supports that this missense variant does not alter protein structure/function; This variant is associated with the following publications: (PMID: 31980526, 30507656, 19940839, 30595564, 15698423, 12846734, 15108281, 18503009, 30650191, 16133180, 19914852, 15108277, 12874454)

The PKHD1 c.9530T>C variant is predicted to result in the amino acid substitution p.Ile3177Thr. This variant has been reported in several patients with polycystic kidney disease. In the majority of patients, it was detected in combination with the PKHD1 variant c.2414C>T (p.Pro805Leu) (Rossetti et al. 2003. PubMed ID: 12846734; Shuster et al. 2019. PubMed ID: 30650191; Bergmann et al. 2004. PubMed ID: 15108281; Denamur et al. 2010. PubMed ID: 19940839; PreventionGenetics). In at least four of these patients familial testing confirmed these variants were inherited as a haplotype (in cis) on the same allele (c.[2414C>T;9530T>C] p.[Pro805Leu;Ile3177Thr]), and this haplotype was in trans with a second PKHD1 variant allele (Rossetti et al. 2003. PubMed ID: 12846734 ; Shuster. 2019. PubMed ID: 30650191; Bergmann et al. 2004. PubMed ID: 15108281). However, the c.9530T>C (p.Ile3177Thr) variant has also been reported in individuals with polycystic kidney disease without p.Pro805Leu (Rossetti et al. 2003. PubMed ID: 12846734; PreventionGenetics). In one case, it was shown to be in trans with the suspected pathogenic variant c.2269A>C (p.Ile757Leu) (Rossetti et al. 2003. PubMed ID: 12846734). The c.9530T>C (p.Ile3177Thr) variant is reported in 0.011% of alleles in individuals of European (Non-Finnish) descent in gnomAD (http://gnomad.broadinstitute.org/variant/6-51612884-A-G). In conclusion, the haplotype c.[2414C>T;9530T>C] p.[Pro805Leu;Ile3177Thr] is considered to be pathogenic; however, the contribution of each variant is unknown. Although we suspect the c.9530T>C (p.Ile3177Thr) variant may be pathogenic, at this time the clinical significance of this variant is uncertain.

This sequence change replaces isoleucine, which is neutral and non-polar, with threonine, which is neutral and polar, at codon 3177 of the PKHD1 protein (p.Ile3177Thr). This variant is present in population databases (rs200511261, gnomAD 0.01%). This missense change has been observed in individual(s) with polycystic kidney disease on the same chromosome with another PKHD1 variant (p.Pro805Leu)(PMID: 16133180, 15108281, 18503009, 19940839). The haplotype (Pro805Leu; Ile3177Thr) has been observed on the opposite chromosome from other pathogenic variants in an individuals affected with polycystic kidney disease (PMID: 12846734, 15108281, Invitae). ClinVar contains an entry for this variant (Variation ID: 377018). 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 PKHD1 protein function. In summary, the available evidence is currently insufficient to determine the role of this variant in disease. Therefore, it has been classified as a Variant of Uncertain Significance.

The PKHD1 p.Ile3177Thr variant was identified in 10 of 974 proband chromosomes (frequency: 0.01) from individuals or families with ARPKD (Bergmann 2005, Denamur 2010, Furu 2004, Gunay-Aygun 2010, Losekoot 2005, Rosetti 2003).The variant was also identified in dbSNP (ID: rs200511261), Clinvitae database (as pathogenic by Emory genetics) RWTH AAachen University ARPKD database (as pathogenic) and PKHD1-LOVD. This variant was identified in the NHLBI GO Exome Sequencing Project in 1 of 8600 European American alleles (freq. 0.0001) and Exome Aggregation Consortium database (March 14, 2016) in 5 of 66720 chromosomes (freq. 7.49E-05) in the European population, this low number of observations and low frequency is not substantive enough to determine the prevalence of the variant in the general population and its relationship to disease. The p.Ile3177 residue is not conserved in mammals and computational analyses (PolyPhen-2, SIFT, AlignGVGD, BLOSUM, MutationTaster) provide inconsistent predictions regarding the impact to the protein; this information is not very predictive of pathogenicity. The variant occurs outside of the splicing consensus sequence and 1 of 5 in silico or computational prediction software programs (SpliceSiteFinder, MaxEntScan, NNSPLICE, GeneSplicer, HumanSpliceFinder) predict a greater than 10% difference in splicing; this is not very predictive of pathogenicity. The case studies by Arbeiter (2008) and Denamur (2010) identify this mutation along with evolutionarily highly conserved missense change c.2414CT (p.Pro805Leu) in patients who died perinatally from ARPKD. In addition, several studies found the variant in patients with severe perinatally-fatal phenotype of ARPKD (Bergmann 2005, Furu 2004, Gunay-Aygun 2010, Rosetti 2003, Losekoot 2005). In summary, based on the above information, this variant meets our laboratory’s criteria to be classified as pathogenic.