ClinVar Genomic variation as it relates to human health

PharmGKB Level of Evidence 1A: Level 1A clinical annotations describe variant-drug combinations that have variant-specific prescribing guidance available in a current clinical guideline annotation or an FDA-approved drug label annotation. Annotations of drug labels or clinical guidelines must give prescribing guidance for specific variants (e.g. CYP2C9*3, HLA-B*57:01) or provide mapping from defined allele functions to diplotypes and phenotypes to be used as supporting evidence for a level 1A clinical annotation. Level 1A clinical annotations must also be supported by at least one publication in addition to a clinical guideline or drug label with variant-specific prescribing guidance.

PS3, PP2, PM3_Supporting, PM2

In the published literature, the variant has been associated with mild CF signs and symptoms with compound heterozygous individuals often being pancreatic sufficient, have abnormal sweat chloride levels, and are responsive to therapeutics (PMID: 6840743 (1983), 23974870 (2013), 25732475 (2015), 28392015 (2017)). The variant has been reported to be common in the Scottish population (PMID: 9507391 (1998)). Functional studies have shown that this variant has a damaging effect on CFTR maturation and function (PMID: 23974870 (2013), 23891399 (2014), 27660821 (2016), 33781744 (2021)). Based on the available information, this variant is classified as pathogenic.

This sequence change replaces proline, which is neutral and non-polar, with leucine, which is neutral and non-polar, at codon 67 of the CFTR protein (p.Pro67Leu). This variant is present in population databases (rs368505753, gnomAD 0.006%). This missense change has been observed in individual(s) with cystic fibrosis (CF), congenital bilateral absence of vas deferens, or other CFTR-related conditions (PMID: 9507391, 16840743, 22658665, 23974870). 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: 53425). 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 CFTR protein function with a positive predictive value of 80%. Experimental studies have shown that this missense change affects CFTR function (PMID: 23891399, 23974870). For these reasons, this variant has been classified as Pathogenic.

The CFTR c.200C>T; p.Pro67Leu variant (rs368505753), is reported in the literature in multiple individuals in the compound heterozygous state affected with cystic fibrosis (Gilfillan 1998, Kingsmore 2021, Raraigh 2022, Sosnay 2013). This variant is reported in ClinVar (Variation ID: 53425) and is observed on ten alleles in the Genome Aggregation Database, indicating it is not a common polymorphism and. In vitro/In vivo functional analyses demonstrate altered CFTR protein folding, reduced mature CTFR protein, and reduced chloride transport (Sabusap 2021, Van Goor 2014). The proline at codon 67 is highly conserved and computational analyses predict that this variant is deleterious (REVEL:0.926). Based on available information, this variant is considered to be pathogenic. References: Gilfillan A, et al. P67L: a cystic fibrosis allele with mild effects found at high frequency in the Scottish population. J Med Genet. 1998. PMID: 9507391 Kingsmore SF, et al. A genome sequencing system for universal newborn screening, diagnosis, and precision medicine for severe genetic diseases. 2021. Am J Hum Genet. PMID: 36007526. Raraigh KS, et al. Complete CFTR gene sequencing in 5,058 individuals with cystic fibrosis informs variant-specific treatment. J Cyst Fibros. 2022. PMID: 34782259. Sabusap CM, et al. The CFTR P67L variant reveals a key role for N-terminal lasso helices in channel folding, maturation, and pharmacologic rescue. 2021. J Biol Chem. PMID: 33781744. Sosnay PR, et al. Defining the disease liability of variants in the cystic fibrosis transmembrane conductance regulator gene. Nat Genet. 2013. PMID: 23974870. Van Goor F, et al. Effect of ivacaftor on CFTR forms with missense mutations associated with defects in protein processing or function. J Cyst Fibros. 2014. PMID: 23891399.

The p.P67L pathogenic mutation (also known as c.200C>T), located in coding exon 3 of the CFTR gene, results from a C to T substitution at nucleotide position 200. The proline at codon 67 is replaced by leucine, an amino acid with similar properties. This mutation has been described in a Scottish cohort of individuals with a mild phenotype, including in trans with p.G542* in an 18-year-old male with recurrent chest infections and pancreatic insufficiency as well as in trans with p.F508del in a 1-year-old female with a probable diagnosis of cystic fibrosis (CF) and an initial abnormal sweat chloride level followed by two equivocal sweat chloride tests (Gilfillan A et al. J. Med. Genet., 1998 Feb;35:122-5). In vitro functional studies showed that while CFTR transcripts with this pathogenic mutation had similar mRNA levels compared to wildtype, the amount of processed mature protein was significantly decreased (Van Goor F et al. J. Cyst. Fibros., 2014 Jan;13:29-36). This mutation is associated with borderline sweat chloride levels and pancreatic sufficiency (Sosnay PR et al. Nat. Genet., 2013 Oct;45:1160-7). Based on the supporting evidence, this alteration is interpreted as a disease-causing mutation.

PS3, PM2, PM3_strong, PP3, PP4, PP5

Variant summary: The CFTR c.200C>T (p.Pro67Leu) variant involves the alteration of a conserved nucleotide and is present in ABC transporter type 1, transmembrane domain of the protein. 5/5 in silico tools predict a damaging outcome for this variant. This variant was found in 4/121266 control chromosomes at a frequency of 0.000033, which does not exceed the estimated maximal expected allele frequency of a pathogenic CFTR variant (0.0129603). The variant has been reported in numerous CF-affected individuals in the literature, particularly in patients with non-classic CF with consistent recessive genotypes, and has been shown to display a mean chloride conductance <10% compared to wildtype (Sosnay_2013, Kraus_2007). In addition, multiple clinical diagnostic laboratories/reputable databases have classified this variant as pathogenic. Taken together, this variant is classified as pathogenic.

Disease-causing CFTR variant (previously reported for this patient by mass spectrometry genotyping). See www.CFTR2.org for phenotype information.

This variant has been previously reported as a compound heterozygous change in many individuals affected with cystic fibrosis (CF), congenital bilateral absence of vas deferens, or other CFTR-related conditions (PMID: 9507391, 22658665, 23974870, 16840743). Individuals with this variant and a second pathogenic allele are typically found to have lower sweat chloride levels than the average CF (http://cftr2.org/mutation/scientific/P67L/). Experimental studies have shown that this missense change affects the chloride conduction function in vitro (PMID:23974870, 23891399). It is present in the heterozygous state in the gnomAD population database at a frequency of 0.004% (10/282408) and thus is presumed to be rare. In silico analyses support a deleterious effect of the c.200C>T (p.Pro67Leu) variant on protein function. Based on the available evidence, the c.200C>T (p.Pro67Leu) variant is classified as Pathogenic.

This variant has been previously reported as a compound heterozygous change in multiple individuals with cystic fibrosis (CF) and other CFTR-related disorders (PMID: 9507391, 22658665, 23974870, 16840743). The c.200C>T (p.Pro67Leu) variant is present in the CFTR2 website as a CF disease-causing variant when combined with another CF-causing variant (http://cftr2.org/mutation/scientific/P67L/). In-vitro functional studies showed that this alteration affects the channel function (PMID:23974870, 23891399). It is present in the heterozygous state in the gnomAD population database at a frequency of 0.004% (10/282408) and thus is presumed to be rare. In silico analyses support a deleterious effect of the c.200C>T (p.Pro67Leu) variant on protein function. Based on the available evidence, the c.200C>T (p.Pro67Leu) variant is classified as Pathogenic.

The CFTR c.200C>T variant is predicted to result in the amino acid substitution p.Pro67Leu. This variant has been reported to be causative for cystic fibrosis (https://cftr2.org, Sosnay et al. 2013. PubMed ID: 23974870; Claustres et al. 1993. PubMed ID: 7691344). In summary, we classify this variant as pathogenic.